pre- and post-snapshot hooks

* stack-based execution model, documented in documentation
* circbuf for capturing hook output
* built-in hooks for postgres and mysql
* refactor docs, too much info on the jobs page, too difficult
  to discover snapshotting & hooks

Co-authored-by: Ross Williams <ross@ross-williams.net>
Co-authored-by: Christian Schwarz <me@cschwarz.com>

fixes #74

config/config.go

@@ -139,6 +139,7 @@ type SnapshottingPeriodic struct {
 	Type     string        `yaml:"type"`
 	Prefix   string        `yaml:"prefix"`
 	Interval time.Duration `yaml:"interval,positive"`
+	Hooks    HookList      `yaml:"hooks,optional"`
 }
 
 type SnapshottingManual struct {
@@ -361,6 +362,38 @@ type JobDebugSettings struct {
 	RPCLog bool `yaml:"rpc_log,optional,default=false"`
 }
 
+type HookList []HookEnum
+
+type HookEnum struct {
+	Ret interface{}
+}
+
+type HookCommand struct {
+	Path               string            `yaml:"path"`
+	Timeout            time.Duration     `yaml:"timeout,optional,positive,default=30s"`
+	Filesystems        FilesystemsFilter `yaml:"filesystems,optional,default={'<': true}"`
+	HookSettingsCommon `yaml:",inline"`
+}
+
+type HookPostgresCheckpoint struct {
+	HookSettingsCommon `yaml:",inline"`
+	DSN                string            `yaml:"dsn"`
+	Timeout            time.Duration     `yaml:"timeout,optional,positive,default=30s"`
+	Filesystems        FilesystemsFilter `yaml:"filesystems"` // required, user should not CHECKPOINT for every FS
+}
+
+type HookMySQLLockTables struct {
+	HookSettingsCommon `yaml:",inline"`
+	DSN                string            `yaml:"dsn"`
+	Timeout            time.Duration     `yaml:"timeout,optional,positive,default=30s"`
+	Filesystems        FilesystemsFilter `yaml:"filesystems"`
+}
+
+type HookSettingsCommon struct {
+	Type       string `yaml:"type"`
+	ErrIsFatal bool   `yaml:"err_is_fatal,optional,default=false"`
+}
+
 func enumUnmarshal(u func(interface{}, bool) error, types map[string]interface{}) (interface{}, error) {
 	var in struct {
 		Type string
@@ -501,6 +534,15 @@ func (t *SyslogFacility) UnmarshalYAML(u func(interface{}, bool) error) (err err
 	return nil
 }
 
+func (t *HookEnum) UnmarshalYAML(u func(interface{}, bool) error) (err error) {
+	t.Ret, err = enumUnmarshal(u, map[string]interface{}{
+		"command":             &HookCommand{},
+		"postgres-checkpoint": &HookPostgresCheckpoint{},
+		"mysql-lock-tables":   &HookMySQLLockTables{},
+	})
+	return
+}
+
 var ConfigFileDefaultLocations = []string{
 	"/etc/zrepl/zrepl.yml",
 	"/usr/local/etc/zrepl/zrepl.yml",

config/config_snapshotting_test.go

@@ -38,6 +38,29 @@ jobs:
     interval: 10m
 `
 
+	hooks := `
+  snapshotting:
+    type: periodic
+    prefix: zrepl_
+    interval: 10m
+    hooks:
+    - type: command
+      path: /tmp/path/to/command
+    - type: command
+      path: /tmp/path/to/command
+      filesystems: { "zroot<": true, "<": false }
+    - type: postgres-checkpoint
+      dsn: "host=localhost port=5432 user=postgres sslmode=disable"
+      filesystems: {
+          "tank/postgres/data11": true
+      }
+    - type: mysql-lock-tables
+      dsn: "root@tcp(localhost)/"
+      filesystems: {
+        "tank/mysql": true
+      }
+`
+
 	fillSnapshotting := func(s string) string { return fmt.Sprintf(tmpl, s) }
 	var c *Config
 
@@ -55,4 +78,13 @@ jobs:
 		assert.Equal(t, "zrepl_", snp.Prefix)
 	})
 
+	t.Run("hooks", func(t *testing.T) {
+		c = testValidConfig(t, fillSnapshotting(hooks))
+		hs := c.Jobs[0].Ret.(*PushJob).Snapshotting.Ret.(*SnapshottingPeriodic).Hooks
+		assert.Equal(t, hs[0].Ret.(*HookCommand).Filesystems["<"], true)
+		assert.Equal(t, hs[1].Ret.(*HookCommand).Filesystems["zroot<"], true)
+		assert.Equal(t, hs[2].Ret.(*HookPostgresCheckpoint).Filesystems["tank/postgres/data11"], true)
+		assert.Equal(t, hs[3].Ret.(*HookMySQLLockTables).Filesystems["tank/mysql"], true)
+	})
+
 }

config/samples/hooks/template.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+set -e
+
+[ "$ZREPL_DRYRUN" = "true" ] && DRYRUN="echo DRYRUN: "
+
+pre_snapshot() {
+    $DRYRUN date
+}
+
+post_snapshot() {
+    $DRYRUN date
+}
+
+case "$ZREPL_HOOKTYPE" in
+    pre_snapshot|post_snapshot)
+        "$ZREPL_HOOKTYPE"
+        ;;
+    *)
+        printf 'Unrecognized hook type: %s\n' "$ZREPL_HOOKTYPE"
+        exit 255
+        ;;
+esac

daemon/hooks/edge_string.go

@@ -0,0 +1,35 @@
+// Code generated by "stringer -type=Edge"; DO NOT EDIT.
+
+package hooks
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[Pre-1]
+	_ = x[Callback-2]
+	_ = x[Post-4]
+}
+
+const (
+	_Edge_name_0 = "PreCallback"
+	_Edge_name_1 = "Post"
+)
+
+var (
+	_Edge_index_0 = [...]uint8{0, 3, 11}
+)
+
+func (i Edge) String() string {
+	switch {
+	case 1 <= i && i <= 2:
+		i -= 1
+		return _Edge_name_0[_Edge_index_0[i]:_Edge_index_0[i+1]]
+	case i == 4:
+		return _Edge_name_1
+	default:
+		return "Edge(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+}

daemon/hooks/hook_config.go

@@ -0,0 +1,52 @@
+package hooks
+
+import (
+	"fmt"
+
+	"github.com/zrepl/zrepl/config"
+	"github.com/zrepl/zrepl/zfs"
+)
+
+type List []Hook
+
+func HookFromConfig(in config.HookEnum) (Hook, error) {
+	switch v := in.Ret.(type) {
+	case *config.HookCommand:
+		return NewCommandHook(v)
+	case *config.HookPostgresCheckpoint:
+		return PgChkptHookFromConfig(v)
+	case *config.HookMySQLLockTables:
+		return MyLockTablesFromConfig(v)
+	default:
+		return nil, fmt.Errorf("unknown hook type %T", v)
+	}
+}
+
+func ListFromConfig(in *config.HookList) (r *List, err error) {
+	hl := make(List, len(*in))
+
+	for i, h := range *in {
+		hl[i], err = HookFromConfig(h)
+		if err != nil {
+			return nil, fmt.Errorf("create hook #%d: %s", i+1, err)
+		}
+	}
+
+	return &hl, nil
+}
+
+func (l List) CopyFilteredForFilesystem(fs *zfs.DatasetPath) (ret List, err error) {
+	ret = make(List, 0, len(l))
+
+	for _, h := range l {
+		var passFilesystem bool
+		if passFilesystem, err = h.Filesystems().Filter(fs); err != nil {
+			return nil, err
+		}
+		if passFilesystem {
+			ret = append(ret, h)
+		}
+	}
+
+	return ret, nil
+}

daemon/hooks/hook_docs.go

@@ -0,0 +1,34 @@
+// Package hooks implements pre- and post snapshot hooks.
+//
+// Plan is a generic executor for ExpectStepReports before and after an activity specified in a callback.
+// It provides a reporting facility that can be polled while the plan is executing to gather progress information.
+//
+// This package also provides all supported hook type implementations and abstractions around them.
+//
+// Use For Other Kinds Of ExpectStepReports
+//
+// This package REQUIRES REFACTORING before it can be used for other activities than snapshots, e.g. pre- and post-replication:
+//
+// The Hook interface requires a hook to provide a Filesystems() filter, which doesn't make sense for
+// all kinds of activities.
+//
+// The hook implementations should move out of this package.
+// However, there is a lot of tight coupling which to untangle isn't worth it ATM.
+//
+// How This Package Is Used By Package Snapper
+//
+// Deserialize a config.List using ListFromConfig().
+// Then it MUST filter the list to only contain hooks for a particular filesystem using
+// hooksList.CopyFilteredForFilesystem(fs).
+//
+// Then create a CallbackHook using NewCallbackHookForFilesystem().
+//
+// Pass all of the above to NewPlan() which provides a Report() and Run() method:
+//
+// Plan.Run(ctx context.Context,dryRun bool) executes the plan and take a context as argument that should contain a logger added using hooks.WithLogger()).
+// The value of dryRun is passed through to the hooks' Run() method.
+// Command hooks make it available in the environment variable ZREPL_DRYRUN.
+//
+// Plan.Report() can be called while Plan.Run() is executing to give an overview of plan execution progress (future use in "zrepl status").
+//
+package hooks

daemon/hooks/hook_exec.go

@@ -0,0 +1,292 @@
+package hooks
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/zrepl/zrepl/zfs"
+)
+
+// Re-export type here so that
+// every file in package hooks doesn't
+// have to import github.com/zrepl/zrepl/zfs
+type Filter zfs.DatasetFilter
+
+type Hook interface {
+	Filesystems() Filter
+
+	// If true and the Pre edge invocation of Run fails, Post edge will not run and other Pre edges will not run.
+	ErrIsFatal() bool
+
+	// Run is invoked by HookPlan for a Pre edge.
+	// If HookReport.HadError() == false, the Post edge will be invoked, too.
+	Run(ctx context.Context, edge Edge, phase Phase, dryRun bool, extra Env, state map[interface{}]interface{}) HookReport
+
+	String() string
+}
+
+type Phase string
+
+const (
+	PhaseSnapshot = Phase("snapshot")
+	PhaseTesting  = Phase("testing")
+)
+
+func (p Phase) String() string {
+	return string(p)
+}
+
+//go:generate stringer -type=Edge
+type Edge uint
+
+const (
+	Pre = Edge(1 << iota)
+	Callback
+	Post
+)
+
+func (e Edge) StringForPhase(phase Phase) string {
+	return fmt.Sprintf("%s_%s", e.String(), phase.String())
+}
+
+//go:generate enumer -type=StepStatus -trimprefix=Step
+type StepStatus int
+
+const (
+	StepPending StepStatus = 1 << iota
+	StepExec
+	StepOk
+	StepErr
+	StepSkippedDueToFatalErr
+	StepSkippedDueToPreErr
+)
+
+type HookReport interface {
+	String() string
+	HadError() bool
+	Error() string
+}
+
+type Step struct {
+	Hook       Hook
+	Edge       Edge
+	Status     StepStatus
+	Begin, End time.Time
+	// Report may be nil
+	// FIXME cannot serialize this for client status, but contains interesting info (like what error happened)
+	Report     HookReport
+	state      map[interface{}]interface{}
+}
+
+func (s Step) String() (out string) {
+	fatal := "~"
+	if s.Hook.ErrIsFatal() && s.Edge == Pre {
+		fatal = "!"
+	}
+	runTime := "..."
+	if s.Status != StepPending {
+		t := s.End.Sub(s.Begin)
+		runTime = t.Round(time.Millisecond).String()
+	}
+	return fmt.Sprintf("[%s] [%5s] %s [%s]  %s", s.Status, runTime, fatal, s.Edge, s.Hook)
+}
+
+type Plan struct {
+	mtx sync.RWMutex
+
+	steps []*Step
+	pre   []*Step // protected by mtx
+	cb    *Step
+	post  []*Step // not reversed, i.e. entry at index i corresponds to pre-edge in pre[i]
+
+	phase Phase
+	env   Env
+}
+
+func NewPlan(hooks *List, phase Phase, cb *CallbackHook, extra Env) (*Plan, error) {
+
+	var pre, post []*Step
+	// TODO sanity check unique name of hook?
+	for _, hook := range *hooks {
+		state := make(map[interface{}]interface{})
+		preE := &Step{
+			Hook:   hook,
+			Edge:   Pre,
+			Status: StepPending,
+			state:  state,
+		}
+		pre = append(pre, preE)
+		postE := &Step{
+			Hook:   hook,
+			Edge:   Post,
+			Status: StepPending,
+			state:  state,
+		}
+		post = append(post, postE)
+	}
+
+	cbE := &Step{
+		Hook:   cb,
+		Edge:   Callback,
+		Status: StepPending,
+	}
+
+	steps := make([]*Step, 0, len(pre)+len(post)+1)
+	steps = append(steps, pre...)
+	steps = append(steps, cbE)
+	for i := len(post) - 1; i >= 0; i-- {
+		steps = append(steps, post[i])
+	}
+
+	plan := &Plan{
+		phase: phase,
+		env:   extra,
+		steps: steps,
+		pre:   pre,
+		post:  post,
+		cb:    cbE,
+	}
+
+	return plan, nil
+}
+
+type PlanReport []Step
+
+func (p *Plan) Report() PlanReport {
+	p.mtx.RLock()
+	defer p.mtx.RUnlock()
+	rep := make([]Step, len(p.steps))
+	for i := range rep {
+		rep[i] = *p.steps[i]
+	}
+	return rep
+}
+
+func (r PlanReport) HadError() bool {
+	for _, e := range r {
+		if e.Status == StepErr {
+			return true
+		}
+	}
+	return false
+}
+
+func (r PlanReport) HadFatalError() bool {
+	for _, e := range r {
+		if e.Status == StepSkippedDueToFatalErr {
+			return true
+		}
+	}
+	return false
+}
+
+func (r PlanReport) String() string {
+	stepStrings := make([]string, len(r))
+	for i, e := range r {
+		stepStrings[i] = fmt.Sprintf("%02d %s", i+1, e)
+	}
+	return strings.Join(stepStrings, "\n")
+}
+
+func (p *Plan) Run(ctx context.Context, dryRun bool) {
+	p.mtx.RLock()
+	defer p.mtx.RUnlock()
+	w := func(f func()) {
+		p.mtx.RUnlock()
+		defer p.mtx.RLock()
+		p.mtx.Lock()
+		defer p.mtx.Unlock()
+		f()
+	}
+	runHook := func(s *Step, ctx context.Context, edge Edge) HookReport {
+		w(func() { s.Status = StepExec })
+		begin := time.Now()
+		r := s.Hook.Run(ctx, edge, p.phase, dryRun, p.env, s.state)
+		end := time.Now()
+		w(func() {
+			s.Report = r
+			s.Status = StepOk
+			if r.HadError() {
+				s.Status = StepErr
+			}
+			s.Begin, s.End = begin, end
+		})
+		return r
+	}
+
+	l := getLogger(ctx)
+
+	// it's a stack, execute until we reach the end of the list (last item in)
+	// or fail inbetween
+	l.Info("run pre-edges in configuration order")
+	next := 0
+	for ; next < len(p.pre); next++ {
+		e := p.pre[next]
+		l := l.WithField("hook", e.Hook)
+		r := runHook(e, ctx, Pre)
+		if r.HadError() {
+			l.WithError(r).Error("hook invocation failed for pre-edge")
+			if e.Hook.ErrIsFatal() {
+				l.Error("the hook run was aborted due to a fatal error in this hook")
+				break
+			}
+		}
+	}
+
+	hadFatalErr := next != len(p.pre)
+	if hadFatalErr {
+		l.Error("fatal error in a pre-snapshot hook invocation")
+		l.Error("no snapshot will be taken")
+		l.Error("only running post-edges for successful pre-edges")
+		w(func() {
+			p.post[next].Status = StepSkippedDueToFatalErr
+			for i := next + 1; i < len(p.pre); i++ {
+				p.pre[i].Status = StepSkippedDueToFatalErr
+				p.post[i].Status = StepSkippedDueToFatalErr
+			}
+			p.cb.Status = StepSkippedDueToFatalErr
+		})
+		return
+	}
+
+	l.Info("running callback")
+	cbR := runHook(p.cb, ctx, Callback)
+	if cbR.HadError() {
+		l.WithError(cbR).Error("callback failed")
+	}
+
+	l.Info("run post-edges for successful pre-edges in reverse configuration order")
+
+	// the constructor produces pre and post entries
+	// post is NOT reversed
+	next-- // now at index of last executed pre-edge
+	for ; next >= 0; next-- {
+		e := p.post[next]
+		l := l.WithField("hook", e.Hook)
+
+		if p.pre[next].Status != StepOk {
+			if p.pre[next].Status != StepErr {
+				panic(fmt.Sprintf("expecting a pre-edge hook report to be either Ok or Err, got %s", p.pre[next].Status))
+			}
+			l.Info("skip post-edge because pre-edge failed")
+			w(func() {
+				e.Status = StepSkippedDueToPreErr
+			})
+			continue
+		}
+
+		report := runHook(e, ctx, Post)
+
+		if report.HadError() {
+			l.WithError(report).Error("hook invocation failed for post-edge")
+			l.Error("subsequent post-edges run regardless of this post-edge failure")
+		}
+
+		// ErrIsFatal is only relevant for Pre
+
+	}
+
+}

daemon/hooks/hook_logging.go

@@ -0,0 +1,103 @@
+package hooks
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"sync"
+
+	"github.com/zrepl/zrepl/logger"
+	"github.com/zrepl/zrepl/util/envconst"
+)
+
+type contextKey int
+
+const (
+	contextKeyLog contextKey = 0
+)
+
+type Logger = logger.Logger
+
+func WithLogger(ctx context.Context, log Logger) context.Context {
+	return context.WithValue(ctx, contextKeyLog, log)
+}
+
+func GetLogger(ctx context.Context) Logger { return getLogger(ctx) }
+
+func getLogger(ctx context.Context) Logger {
+	if log, ok := ctx.Value(contextKeyLog).(Logger); ok {
+		return log
+	}
+	return logger.NewNullLogger()
+}
+
+const MAX_HOOK_LOG_SIZE_DEFAULT int = 1 << 20
+
+type logWriter struct {
+	/*
+		Mutex prevents:
+			concurrent writes to buf, scanner in Write([]byte)
+			data race on scanner vs Write([]byte)
+				and concurrent write to buf (call to buf.Reset())
+				in Close()
+
+		(Also, Close() should generally block until any Write() call completes.)
+	*/
+	mtx     *sync.Mutex
+	buf     bytes.Buffer
+	scanner *bufio.Scanner
+	logger  Logger
+	level   logger.Level
+	field   string
+}
+
+func NewLogWriter(mtx *sync.Mutex, logger Logger, level logger.Level, field string) *logWriter {
+	w := new(logWriter)
+	w.mtx = mtx
+	w.scanner = bufio.NewScanner(&w.buf)
+	w.logger = logger
+	w.level = level
+	w.field = field
+	return w
+}
+
+func (w *logWriter) log(line string) {
+	w.logger.WithField(w.field, line).Log(w.level, "hook output")
+}
+
+func (w *logWriter) logUnreadBytes() error {
+	for w.scanner.Scan() {
+		w.log(w.scanner.Text())
+	}
+	if w.buf.Cap() > envconst.Int("ZREPL_MAX_HOOK_LOG_SIZE", MAX_HOOK_LOG_SIZE_DEFAULT) {
+		w.buf.Reset()
+	}
+
+	return nil
+}
+
+func (w *logWriter) Write(in []byte) (int, error) {
+	w.mtx.Lock()
+	defer w.mtx.Unlock()
+
+	n, bufErr := w.buf.Write(in)
+	if bufErr != nil {
+		return n, bufErr
+	}
+
+	err := w.logUnreadBytes()
+	if err != nil {
+		return n, err
+	}
+	// Always reset the scanner for the next Write
+	w.scanner = bufio.NewScanner(&w.buf)
+
+	return n, nil
+}
+
+func (w *logWriter) Close() (err error) {
+	w.mtx.Lock()
+	defer w.mtx.Unlock()
+
+	return w.logUnreadBytes()
+}

daemon/hooks/hook_type_callback.go

@@ -0,0 +1,65 @@
+package hooks
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/zrepl/zrepl/daemon/filters"
+	"github.com/zrepl/zrepl/zfs"
+)
+
+type HookJobCallback func(ctx context.Context) error
+
+type CallbackHook struct {
+	cb            HookJobCallback
+	filter        Filter
+	displayString string
+}
+
+func NewCallbackHookForFilesystem(displayString string, fs *zfs.DatasetPath, cb HookJobCallback) *CallbackHook {
+	filter, _ := filters.DatasetMapFilterFromConfig(map[string]bool{fs.ToString(): true})
+	return NewCallbackHook(displayString, cb, filter)
+}
+
+func NewCallbackHook(displayString string, cb HookJobCallback, filter Filter) *CallbackHook {
+	return &CallbackHook{
+		cb:            cb,
+		filter:        filter,
+		displayString: displayString,
+	}
+}
+
+func (h *CallbackHook) Filesystems() Filter {
+	return h.filter
+}
+
+func (h *CallbackHook) ErrIsFatal() bool {
+	return false // callback is by definition
+}
+
+func (h *CallbackHook) String() string {
+	return h.displayString
+}
+
+type CallbackHookReport struct {
+	Name string
+	Err  error
+}
+
+func (r *CallbackHookReport) String() string {
+	if r.HadError() {
+		return r.Error()
+	}
+	return r.Name
+}
+
+func (r *CallbackHookReport) HadError() bool { return r.Err != nil }
+
+func (r *CallbackHookReport) Error() string {
+	return fmt.Sprintf("%s error: %s", r.Name, r.Err)
+}
+
+func (h *CallbackHook) Run(ctx context.Context, edge Edge, phase Phase, dryRun bool, extra Env, state map[interface{}]interface{}) HookReport {
+	err := h.cb(ctx)
+	return &CallbackHookReport{h.displayString, err}
+}

daemon/hooks/hook_type_command.go

@@ -0,0 +1,192 @@
+package hooks
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"math"
+	"os"
+	"os/exec"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/zrepl/zrepl/config"
+	"github.com/zrepl/zrepl/daemon/filters"
+	"github.com/zrepl/zrepl/logger"
+	"github.com/zrepl/zrepl/util/circlog"
+	"github.com/zrepl/zrepl/util/envconst"
+)
+
+type HookEnvVar string
+
+const (
+	EnvType     HookEnvVar = "ZREPL_HOOKTYPE"
+	EnvDryRun   HookEnvVar = "ZREPL_DRYRUN"
+	EnvFS       HookEnvVar = "ZREPL_FS"
+	EnvSnapshot HookEnvVar = "ZREPL_SNAPNAME"
+	EnvTimeout  HookEnvVar = "ZREPL_TIMEOUT"
+)
+
+type Env map[HookEnvVar]string
+
+func NewHookEnv(edge Edge, phase Phase, dryRun bool, timeout time.Duration, extra Env) Env {
+	r := Env{
+		EnvTimeout: fmt.Sprintf("%.f", math.Floor(timeout.Seconds())),
+	}
+
+	edgeString := edge.StringForPhase(phase)
+	r[EnvType] = strings.ToLower(edgeString)
+
+	var dryRunString string
+	if dryRun {
+		dryRunString = "true"
+	} else {
+		dryRunString = ""
+	}
+	r[EnvDryRun] = dryRunString
+
+	for k, v := range extra {
+		r[k] = v
+	}
+
+	return r
+}
+
+type CommandHook struct {
+	edge       Edge
+	filter     Filter
+	errIsFatal bool
+	command    string
+	timeout    time.Duration
+}
+
+type CommandHookReport struct {
+	Command                      string
+	Args                         []string // currently always empty
+	Env                          Env
+	Err                          error
+	CapturedStdoutStderrCombined []byte
+}
+
+func (r *CommandHookReport) String() string {
+	// Reproduces a POSIX shell-compatible command line
+	var cmdLine strings.Builder
+	sep := ""
+
+	// Make sure environment variables are always
+	// printed in the same order
+	var hookEnvKeys []HookEnvVar
+	for k := range r.Env {
+		hookEnvKeys = append(hookEnvKeys, k)
+	}
+	sort.Slice(hookEnvKeys, func(i, j int) bool { return string(hookEnvKeys[i]) < string(hookEnvKeys[j]) })
+
+	for _, k := range hookEnvKeys {
+		cmdLine.WriteString(fmt.Sprintf("%s%s='%s'", sep, k, r.Env[k]))
+		sep = " "
+	}
+
+	cmdLine.WriteString(fmt.Sprintf("%s%s", sep, r.Command))
+	for _, a := range r.Args {
+		cmdLine.WriteString(fmt.Sprintf("%s'%s'", sep, a))
+	}
+
+	return fmt.Sprintf("command hook invocation: \"%s\"", cmdLine.String()) // no %q to make copy-pastable
+}
+func (r *CommandHookReport) Error() string {
+	if r.Err == nil {
+		return ""
+	}
+	return fmt.Sprintf("%s FAILED with error: %s", r.String(), r.Err)
+}
+
+func (r *CommandHookReport) HadError() bool {
+	return r.Err != nil
+}
+
+func NewCommandHook(in *config.HookCommand) (r *CommandHook, err error) {
+	r = &CommandHook{
+		errIsFatal: in.ErrIsFatal,
+		command:    in.Path,
+		timeout:    in.Timeout,
+	}
+
+	r.filter, err = filters.DatasetMapFilterFromConfig(in.Filesystems)
+	if err != nil {
+		return nil, fmt.Errorf("cannot parse filesystem filter: %s", err)
+	}
+
+	r.edge = Pre | Post
+
+	return r, nil
+}
+
+func (h *CommandHook) Filesystems() Filter {
+	return h.filter
+}
+
+func (h *CommandHook) ErrIsFatal() bool {
+	return h.errIsFatal
+}
+
+func (h *CommandHook) String() string {
+	return h.command
+}
+
+func (h *CommandHook) Run(ctx context.Context, edge Edge, phase Phase, dryRun bool, extra Env, state map[interface{}]interface{}) HookReport {
+	l := getLogger(ctx).WithField("command", h.command)
+
+	cmdCtx, cancel := context.WithTimeout(ctx, h.timeout)
+	defer cancel()
+
+	cmdExec := exec.CommandContext(cmdCtx, h.command)
+
+	hookEnv := NewHookEnv(edge, phase, dryRun, h.timeout, extra)
+	cmdEnv := os.Environ()
+	for k, v := range hookEnv {
+		cmdEnv = append(cmdEnv, fmt.Sprintf("%s=%s", k, v))
+	}
+	cmdExec.Env = cmdEnv
+
+	var scanMutex sync.Mutex
+	combinedOutput, err := circlog.NewCircularLog(envconst.Int("ZREPL_MAX_HOOK_LOG_SIZE", MAX_HOOK_LOG_SIZE_DEFAULT))
+	if err != nil {
+		return &CommandHookReport{Err: err}
+	}
+	logErrWriter := NewLogWriter(&scanMutex, l, logger.Warn, "stderr")
+	logOutWriter := NewLogWriter(&scanMutex, l, logger.Info, "stdout")
+	defer logErrWriter.Close()
+	defer logOutWriter.Close()
+
+	cmdExec.Stderr = io.MultiWriter(logErrWriter, combinedOutput)
+	cmdExec.Stdout = io.MultiWriter(logOutWriter, combinedOutput)
+
+	report := &CommandHookReport{
+		Command: h.command,
+		Env:     hookEnv,
+		// no report.Args
+	}
+
+	err = cmdExec.Start()
+	if err != nil {
+		report.Err = err
+		return report
+	}
+
+	err = cmdExec.Wait()
+	combinedOutputBytes := combinedOutput.Bytes()
+	report.CapturedStdoutStderrCombined = make([]byte, len(combinedOutputBytes))
+	copy(report.CapturedStdoutStderrCombined, combinedOutputBytes)
+	if err != nil {
+		if cmdCtx.Err() == context.DeadlineExceeded {
+			report.Err = fmt.Errorf("timed out after %s: %s", h.timeout, err)
+			return report
+		}
+		report.Err = err
+		return report
+	}
+
+	return report
+}

daemon/hooks/hook_type_mysql_lock_tables.go

@@ -0,0 +1,145 @@
+package hooks
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"strings"
+
+	sqldriver "database/sql/driver"
+
+	"github.com/go-sql-driver/mysql"
+
+	"github.com/pkg/errors"
+
+	"github.com/zrepl/zrepl/config"
+	"github.com/zrepl/zrepl/daemon/filters"
+	"github.com/zrepl/zrepl/zfs"
+)
+
+// https://dev.mysql.com/doc/mysql-backup-excerpt/5.7/en/backup-methods.html
+//
+// Making Backups Using a File System Snapshot:
+//
+//  If you are using a Veritas file system, you can make a backup like this:
+//
+//    	From a client program, execute FLUSH TABLES WITH READ LOCK.
+//    	From another shell, execute mount vxfs snapshot.
+//    	From the first client, execute UNLOCK TABLES.
+//    	Copy files from the snapshot.
+//    	Unmount the snapshot.
+//
+//	Similar snapshot capabilities may be available in other file systems, such as LVM or ZFS.
+type MySQLLockTables struct {
+	errIsFatal  bool
+	connector   sqldriver.Connector
+	filesystems Filter
+}
+
+type myLockTablesStateKey int
+
+const (
+	myLockTablesConnection myLockTablesStateKey = 1 + iota
+)
+
+func MyLockTablesFromConfig(in *config.HookMySQLLockTables) (*MySQLLockTables, error) {
+	conf, err := mysql.ParseDSN(in.DSN)
+	if err != nil {
+		return nil, errors.Wrap(err, "`dsn` invalid")
+	}
+	cn, err := mysql.NewConnector(conf)
+	if err != nil {
+		return nil, errors.Wrap(err, "`connect` invalid")
+	}
+
+	filesystems, err := filters.DatasetMapFilterFromConfig(in.Filesystems)
+	if err != nil {
+		return nil, errors.Wrap(err, "`filesystems` invalid")
+	}
+
+	return &MySQLLockTables{
+		in.ErrIsFatal,
+		cn,
+		filesystems,
+	}, nil
+}
+
+func (h *MySQLLockTables) ErrIsFatal() bool    { return h.errIsFatal }
+func (h *MySQLLockTables) Filesystems() Filter { return h.filesystems }
+func (h *MySQLLockTables) String() string      { return "MySQL FLUSH TABLES WITH READ LOCK" }
+
+type MyLockTablesReport struct {
+	What string
+	Err  error
+}
+
+func (r *MyLockTablesReport) HadError() bool { return r.Err != nil }
+func (r *MyLockTablesReport) Error() string  { return r.String() }
+func (r *MyLockTablesReport) String() string {
+	var s strings.Builder
+	s.WriteString(r.What)
+	if r.Err != nil {
+		fmt.Fprintf(&s, ": %s", r.Err)
+	}
+	return s.String()
+}
+
+func (h *MySQLLockTables) Run(ctx context.Context, edge Edge, phase Phase, dryRun bool, extra Env, state map[interface{}]interface{}) HookReport {
+	fs, ok := extra[EnvFS]
+	if !ok {
+		panic(extra)
+	}
+	dp, err := zfs.NewDatasetPath(fs)
+	if err != nil {
+		panic(err)
+	}
+	if pass, err := h.filesystems.Filter(dp); err != nil {
+		return &MyLockTablesReport{What: "filesystem filter", Err: err}
+	} else if !pass {
+		getLogger(ctx).Debug("filesystem does not match filter, skipping")
+		return &MyLockTablesReport{What: "filesystem filter skipped this filesystem", Err: nil}
+	}
+
+	switch edge {
+	case Pre:
+		err := h.doRunPre(ctx, dp, dryRun, state)
+		return &MyLockTablesReport{"FLUSH TABLES WITH READ LOCK", err}
+	case Post:
+		err := h.doRunPost(ctx, dp, dryRun, state)
+		return &MyLockTablesReport{"UNLOCK TABLES", err}
+	}
+	return &MyLockTablesReport{What: "skipped this edge", Err: nil}
+}
+
+func (h *MySQLLockTables) doRunPre(ctx context.Context, fs *zfs.DatasetPath, dry bool, state map[interface{}]interface{}) (err error) {
+	db := sql.OpenDB(h.connector)
+	defer func(err *error) {
+		if *err != nil {
+			db.Close()
+		}
+	}(&err)
+
+	getLogger(ctx).Debug("do FLUSH TABLES WITH READ LOCK")
+	_, err = db.ExecContext(ctx, "FLUSH TABLES WITH READ LOCK")
+	if err != nil {
+		return
+	}
+
+	state[myLockTablesConnection] = db
+
+	return nil
+}
+
+func (h *MySQLLockTables) doRunPost(ctx context.Context, fs *zfs.DatasetPath, dry bool, state map[interface{}]interface{}) error {
+
+	db := state[myLockTablesConnection].(*sql.DB)
+	defer db.Close()
+
+	getLogger(ctx).Debug("do UNLOCK TABLES")
+	_, err := db.ExecContext(ctx, "UNLOCK TABLES")
+	if err != nil {
+		return err
+	}
+
+	return nil
+}

daemon/hooks/hook_type_postgres_checkpoint.go

@@ -0,0 +1,98 @@
+package hooks
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"math"
+	"time"
+
+	"github.com/lib/pq"
+	"github.com/pkg/errors"
+
+	"github.com/zrepl/zrepl/config"
+	"github.com/zrepl/zrepl/daemon/filters"
+	"github.com/zrepl/zrepl/zfs"
+)
+
+type PgChkptHook struct {
+	errIsFatal  bool
+	connector   *pq.Connector
+	filesystems Filter
+}
+
+func PgChkptHookFromConfig(in *config.HookPostgresCheckpoint) (*PgChkptHook, error) {
+	filesystems, err := filters.DatasetMapFilterFromConfig(in.Filesystems)
+	if err != nil {
+		return nil, errors.Wrap(err, "`filesystems` invalid")
+	}
+	cn, err := pq.NewConnector(in.DSN)
+	if err != nil {
+		return nil, errors.Wrap(err, "`dsn` invalid")
+	}
+
+	return &PgChkptHook{
+		in.ErrIsFatal,
+		cn,
+		filesystems,
+	}, nil
+}
+
+func (h *PgChkptHook) ErrIsFatal() bool    { return h.errIsFatal }
+func (h *PgChkptHook) Filesystems() Filter { return h.filesystems }
+func (h *PgChkptHook) String() string      { return "postgres checkpoint" }
+
+type PgChkptHookReport struct{ Err error }
+
+func (r *PgChkptHookReport) HadError() bool { return r.Err != nil }
+func (r *PgChkptHookReport) Error() string  { return r.Err.Error() }
+func (r *PgChkptHookReport) String() string {
+	if r.Err != nil {
+		return fmt.Sprintf("postgres CHECKPOINT failed: %s", r.Err)
+	} else {
+		return "postgres CHECKPOINT completed"
+	}
+}
+
+func (h *PgChkptHook) Run(ctx context.Context, edge Edge, phase Phase, dryRun bool, extra Env, state map[interface{}]interface{}) HookReport {
+	if edge != Pre {
+		return &PgChkptHookReport{nil}
+	}
+	fs, ok := extra[EnvFS]
+	if !ok {
+		panic(extra)
+	}
+	dp, err := zfs.NewDatasetPath(fs)
+	if err != nil {
+		panic(err)
+	}
+	err = h.doRunPre(ctx, dp, dryRun)
+	return &PgChkptHookReport{err}
+}
+
+func (h *PgChkptHook) doRunPre(ctx context.Context, fs *zfs.DatasetPath, dry bool) error {
+
+	if pass, err := h.filesystems.Filter(fs); err != nil || !pass {
+		getLogger(ctx).Debug("filesystem does not match filter, skipping")
+		return err
+	}
+
+	db := sql.OpenDB(h.connector)
+	defer db.Close()
+	dl, ok := ctx.Deadline()
+	if ok {
+		timeout := uint64(math.Floor(time.Until(dl).Seconds() * 1000)) // TODO go1.13 milliseconds
+		getLogger(ctx).WithField("statement_timeout", timeout).Debug("setting statement timeout for CHECKPOINT")
+		_, err := db.ExecContext(ctx, "SET statement_timeout TO ?", timeout)
+		if err != nil {
+			return err
+		}
+	}
+	if dry {
+		getLogger(ctx).Debug("dry-run - use ping instead of CHECKPOINT")
+		return db.PingContext(ctx)
+	}
+	getLogger(ctx).Info("execute CHECKPOINT command")
+	_, err := db.ExecContext(ctx, "CHECKPOINT")
+	return err
+}

daemon/hooks/hooks_test.go

@@ -0,0 +1,484 @@
+package hooks_test
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"regexp"
+	"testing"
+	"text/template"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/zrepl/zrepl/config"
+	"github.com/zrepl/zrepl/daemon/hooks"
+	"github.com/zrepl/zrepl/logger"
+	"github.com/zrepl/zrepl/zfs"
+)
+
+type comparisonAssertionFunc func(require.TestingT, interface{}, interface{}, ...interface{})
+type valueAssertionFunc func(require.TestingT, interface{}, ...interface{})
+
+type expectStep struct {
+	ExpectedEdge hooks.Edge
+	ExpectStatus hooks.StepStatus
+	OutputTest   valueAssertionFunc
+	ErrorTest    valueAssertionFunc
+}
+
+type testCase struct {
+	Name           string
+	Config         []string
+	IsSlow         bool
+	SuppressOutput bool
+
+	ExpectCallbackSkipped bool
+	ExpectHadFatalErr     bool
+	ExpectHadError        bool
+	ExpectStepReports     []expectStep
+}
+
+func curryLeft(f comparisonAssertionFunc, expected interface{}) valueAssertionFunc {
+	return curry(f, expected, false)
+}
+
+func curryRight(f comparisonAssertionFunc, expected interface{}) valueAssertionFunc {
+	return curry(f, expected, true)
+}
+
+func curry(f comparisonAssertionFunc, expected interface{}, right bool) (ret valueAssertionFunc) {
+	ret = func(t require.TestingT, s interface{}, v ...interface{}) {
+		var x interface{}
+		var y interface{}
+		if right {
+			x = s
+			y = expected
+		} else {
+			x = expected
+			y = s
+		}
+
+		if len(v) > 0 {
+			f(t, x, y, v)
+		} else {
+			f(t, x, y)
+		}
+	}
+	return
+}
+
+func TestHooks(t *testing.T) {
+	testFSName := "testpool/testdataset"
+	testSnapshotName := "testsnap"
+
+	tmpl, err := template.New("TestHooks").Parse(`
+jobs:
+- name: TestHooks
+  type: snap
+  filesystems: {"<": true}
+  snapshotting:
+    type: periodic
+    interval: 1m
+    prefix: zrepl_snapjob_
+    hooks:
+    {{- template "List" . }}
+  pruning:
+    keep:
+      - type: last_n
+        count: 10
+`)
+	if err != nil {
+		panic(err)
+	}
+
+	regexpTest := func(s string) valueAssertionFunc {
+		return curryLeft(require.Regexp, regexp.MustCompile(s))
+	}
+
+	containsTest := func(s string) valueAssertionFunc {
+		return curryRight(require.Contains, s)
+	}
+
+	testTable := []testCase{
+		testCase{
+			Name: "no_hooks",
+			ExpectStepReports: []expectStep{
+				{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepOk},
+			},
+		},
+		testCase{
+			Name:           "timeout",
+			IsSlow:         true,
+			ExpectHadError: true,
+			Config:         []string{`{type: command, path: {{.WorkDir}}/test/test-timeout.sh, timeout: 2s}`},
+			ExpectStepReports: []expectStep{
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepErr,
+					OutputTest:   containsTest(fmt.Sprintf("TEST pre_testing %s@%s ZREPL_TIMEOUT=2", testFSName, testSnapshotName)),
+					ErrorTest:    regexpTest(`timed out after 2(.\d+)?s`),
+				},
+				expectStep{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepOk},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepSkippedDueToPreErr,
+				},
+			},
+		},
+		testCase{
+			Name:           "check_env",
+			Config:         []string{`{type: command, path: {{.WorkDir}}/test/test-report-env.sh}`},
+			ExpectHadError: false,
+			ExpectStepReports: []expectStep{
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   containsTest(fmt.Sprintf("TEST pre_testing %s@%s", testFSName, testSnapshotName)),
+				},
+				expectStep{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepOk},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   containsTest(fmt.Sprintf("TEST post_testing %s@%s", testFSName, testSnapshotName)),
+				},
+			},
+		},
+
+		testCase{
+			Name:                  "nonfatal_pre_error_continues",
+			ExpectCallbackSkipped: false,
+			ExpectHadError:        true,
+			Config:                []string{`{type: command, path: {{.WorkDir}}/test/test-error.sh}`},
+			ExpectStepReports: []expectStep{
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepErr,
+					OutputTest:   containsTest(fmt.Sprintf("TEST ERROR pre_testing %s@%s", testFSName, testSnapshotName)),
+					ErrorTest:    regexpTest("^command hook invocation.*exit status 1$"),
+				},
+				expectStep{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepOk},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepSkippedDueToPreErr, // post-edge is not executed for failing pre-edge
+				},
+			},
+		},
+
+		testCase{
+			Name:                  "pre_error_fatal_skips_subsequent_pre_edges_and_callback_and_its_post_edge_and_post_edges",
+			ExpectCallbackSkipped: true,
+			ExpectHadFatalErr:     true,
+			ExpectHadError:        true,
+			Config: []string{
+				`{type: command, path: {{.WorkDir}}/test/test-error.sh, err_is_fatal: true}`,
+				`{type: command, path: {{.WorkDir}}/test/test-report-env.sh}`,
+			},
+			ExpectStepReports: []expectStep{
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepErr,
+					OutputTest:   containsTest(fmt.Sprintf("TEST ERROR pre_testing %s@%s", testFSName, testSnapshotName)),
+					ErrorTest:    regexpTest("^command hook invocation.*exit status 1$"),
+				},
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepSkippedDueToFatalErr,
+				},
+				expectStep{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepSkippedDueToFatalErr},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepSkippedDueToFatalErr,
+				},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepSkippedDueToFatalErr,
+				},
+			},
+		},
+
+		testCase{
+			Name:              "post_error_fails_are_ignored_even_if_fatal",
+			ExpectHadFatalErr: false, // only occurs during Post, so it's not a fatal error
+			ExpectHadError:    true,
+			Config: []string{
+				`{type: command, path: {{.WorkDir}}/test/test-post-error.sh, err_is_fatal: true}`,
+				`{type: command, path: {{.WorkDir}}/test/test-report-env.sh}`,
+			},
+			ExpectStepReports: []expectStep{
+				expectStep{
+					// No-action run of test-post-error.sh
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   require.Empty,
+				},
+				expectStep{
+					// Pre run of test-report-env.sh
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   containsTest(fmt.Sprintf("TEST pre_testing %s@%s", testFSName, testSnapshotName)),
+				},
+				expectStep{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepOk},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   containsTest(fmt.Sprintf("TEST post_testing %s@%s", testFSName, testSnapshotName)),
+				},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepErr,
+					OutputTest:   containsTest(fmt.Sprintf("TEST ERROR post_testing %s@%s", testFSName, testSnapshotName)),
+					ErrorTest:    regexpTest("^command hook invocation.*exit status 1$"),
+				},
+			},
+		},
+
+		testCase{
+			Name:   "cleanup_check_env",
+			Config: []string{`{type: command, path: {{.WorkDir}}/test/test-report-env.sh}`},
+			ExpectStepReports: []expectStep{
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   containsTest(fmt.Sprintf("TEST pre_testing %s@%s", testFSName, testSnapshotName)),
+				},
+				expectStep{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepOk},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   containsTest(fmt.Sprintf("TEST post_testing %s@%s", testFSName, testSnapshotName)),
+				},
+			},
+		},
+
+		testCase{
+			Name:              "pre_error_cancels_post",
+			Config:            []string{`{type: command, path: {{.WorkDir}}/test/test-pre-error-post-ok.sh}`},
+			ExpectHadError:    true,
+			ExpectHadFatalErr: false,
+			ExpectStepReports: []expectStep{
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepErr,
+					OutputTest:   containsTest(fmt.Sprintf("TEST ERROR pre_testing %s@%s", testFSName, testSnapshotName)),
+					ErrorTest:    regexpTest("^command hook invocation.*exit status 1$"),
+				},
+				expectStep{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepOk},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepSkippedDueToPreErr,
+				},
+			},
+		},
+
+		testCase{
+			Name: "pre_error_does_not_cancel_other_posts_but_itself",
+			Config: []string{
+				`{type: command, path: {{.WorkDir}}/test/test-report-env.sh}`,
+				`{type: command, path: {{.WorkDir}}/test/test-pre-error-post-ok.sh}`,
+			},
+			ExpectHadError:    true,
+			ExpectHadFatalErr: false,
+			ExpectStepReports: []expectStep{
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   containsTest(fmt.Sprintf("TEST pre_testing %s@%s", testFSName, testSnapshotName)),
+				},
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepErr,
+					OutputTest:   containsTest(fmt.Sprintf("TEST ERROR pre_testing %s@%s", testFSName, testSnapshotName)),
+					ErrorTest:    regexpTest("^command hook invocation.*exit status 1$"),
+				},
+				expectStep{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepOk},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepSkippedDueToPreErr,
+				},
+				expectStep{
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   containsTest(fmt.Sprintf("TEST post_testing %s@%s", testFSName, testSnapshotName)),
+				},
+			},
+		},
+
+		testCase{
+			Name:              "exceed_buffer_limit",
+			SuppressOutput:    true,
+			Config:            []string{`{type: command, path: {{.WorkDir}}/test/test-large-stdout.sh}`},
+			ExpectHadError:    false,
+			ExpectHadFatalErr: false,
+			ExpectStepReports: []expectStep{
+				expectStep{
+					ExpectedEdge: hooks.Pre,
+					ExpectStatus: hooks.StepOk,
+					OutputTest: func(t require.TestingT, s interface{}, v ...interface{}) {
+						require.Len(t, s, 1<<20)
+					},
+				},
+				expectStep{ExpectedEdge: hooks.Callback, ExpectStatus: hooks.StepOk},
+				expectStep{
+					// No-action run of above hook
+					ExpectedEdge: hooks.Post,
+					ExpectStatus: hooks.StepOk,
+					OutputTest:   require.Empty,
+				},
+			},
+		},
+
+		/*
+			Following not intended to test functionality of
+			filter package. Only to demonstrate that hook
+			filters are being applied. The following should
+			result in NO hooks running. If it does run, a
+			fatal hooks.RunReport will be returned.
+		*/
+		testCase{
+			Name: "exclude_all_filesystems",
+			Config: []string{
+				`{type: command, path: {{.WorkDir}}/test/test-error.sh, err_is_fatal: true, filesystems: {"<": false}}`,
+			},
+			ExpectStepReports: []expectStep{
+				expectStep{
+					ExpectedEdge: hooks.Callback,
+					ExpectStatus: hooks.StepOk,
+				},
+			},
+		},
+	}
+
+	parseHookConfig := func(t *testing.T, in string) *config.Config {
+		t.Helper()
+		conf, err := config.ParseConfigBytes([]byte(in))
+		require.NoError(t, err)
+		require.NotNil(t, conf)
+		return conf
+	}
+
+	fillHooks := func(tt *testCase) string {
+		// make hook path absolute
+		cwd, err := os.Getwd()
+		if err != nil {
+			panic("os.Getwd() failed")
+		}
+		var hooksTmpl string = "\n"
+		for _, l := range tt.Config {
+			hooksTmpl += fmt.Sprintf("    - %s\n", l)
+		}
+		tmpl.New("List").Parse(hooksTmpl)
+
+		var outBytes bytes.Buffer
+		data := struct {
+			WorkDir string
+		}{
+			WorkDir: cwd,
+		}
+		if err := tmpl.Execute(&outBytes, data); err != nil {
+			panic(err)
+		}
+
+		return outBytes.String()
+	}
+
+	var c *config.Config
+	fs, err := zfs.NewDatasetPath(testFSName)
+	require.NoError(t, err)
+
+	log := logger.NewTestLogger(t)
+
+	var cbReached bool
+	cb := hooks.NewCallbackHookForFilesystem("testcallback", fs, func(_ context.Context) error {
+		cbReached = true
+		return nil
+	})
+
+	hookEnvExtra := hooks.Env{
+		hooks.EnvFS:       fs.ToString(),
+		hooks.EnvSnapshot: testSnapshotName,
+	}
+
+	for _, tt := range testTable {
+		if testing.Short() && tt.IsSlow {
+			continue
+		}
+
+		t.Run(tt.Name, func(t *testing.T) {
+			c = parseHookConfig(t, fillHooks(&tt))
+			snp := c.Jobs[0].Ret.(*config.SnapJob).Snapshotting.Ret.(*config.SnapshottingPeriodic)
+			hookList, err := hooks.ListFromConfig(&snp.Hooks)
+			require.NoError(t, err)
+
+			filteredHooks, err := hookList.CopyFilteredForFilesystem(fs)
+			require.NoError(t, err)
+			plan, err := hooks.NewPlan(&filteredHooks, hooks.PhaseTesting, cb, hookEnvExtra)
+			require.NoError(t, err)
+			t.Logf("REPORT PRE EXECUTION:\n%s", plan.Report())
+
+			cbReached = false
+
+			ctx := context.Background()
+			if testing.Verbose() && !tt.SuppressOutput {
+				ctx = hooks.WithLogger(ctx, log)
+			}
+			plan.Run(ctx, false)
+			report := plan.Report()
+
+			t.Logf("REPORT POST EXECUTION:\n%s", report)
+
+			/*
+			 * TEST ASSERTIONS
+			 */
+
+			t.Logf("len(runReports)=%v", len(report))
+			t.Logf("len(tt.ExpectStepReports)=%v", len(tt.ExpectStepReports))
+			require.Equal(t, len(tt.ExpectStepReports), len(report), "ExpectStepReports must be same length as expected number of hook runs, excluding possible Callback")
+
+			// Check if callback ran, when required
+			if tt.ExpectCallbackSkipped {
+				require.False(t, cbReached, "callback ran but should not have run")
+			} else {
+				require.True(t, cbReached, "callback should have run but did not")
+			}
+
+			// Check if a fatal run error occurred and was expected
+			require.Equal(t, tt.ExpectHadFatalErr, report.HadFatalError(), "non-matching HadFatalError")
+			require.Equal(t, tt.ExpectHadError, report.HadError(), "non-matching HadError")
+
+			if tt.ExpectHadFatalErr {
+				require.True(t, tt.ExpectHadError, "ExpectHadFatalErr implies ExpectHadError")
+			}
+			if !tt.ExpectHadError {
+				require.False(t, tt.ExpectHadFatalErr, "!ExpectHadError implies !ExpectHadFatalErr")
+			}
+
+			// Iterate through each expected hook run
+			for i, hook := range tt.ExpectStepReports {
+				t.Logf("expecting report conforming to %v", hook)
+
+				exp, act := hook.ExpectStatus, report[i].Status
+				require.Equal(t, exp, act, "%s != %s", exp, act)
+
+				// Check for required ExpectedEdge
+				require.NotZero(t, hook.ExpectedEdge, "each hook must have an ExpectedEdge")
+				require.Equal(t, hook.ExpectedEdge, report[i].Edge,
+					"incorrect edge: expected %q, actual %q", hook.ExpectedEdge.String(), report[i].Edge.String(),
+				)
+
+				// Check for expected output
+				if hook.OutputTest != nil {
+					require.IsType(t, (*hooks.CommandHookReport)(nil), report[i].Report)
+					chr := report[i].Report.(*hooks.CommandHookReport)
+					hook.OutputTest(t, string(chr.CapturedStdoutStderrCombined))
+				}
+
+				// Check for expected errors
+				if hook.ErrorTest != nil {
+					hook.ErrorTest(t, string(report[i].Report.Error()))
+				}
+			}
+
+		})
+	}
+}

daemon/hooks/stepstatus_enumer.go

@@ -0,0 +1,77 @@
+// Code generated by "enumer -type=StepStatus -trimprefix=Step"; DO NOT EDIT.
+
+//
+package hooks
+
+import (
+	"fmt"
+)
+
+const (
+	_StepStatusName_0 = "PendingExec"
+	_StepStatusName_1 = "Ok"
+	_StepStatusName_2 = "Err"
+	_StepStatusName_3 = "SkippedDueToFatalErr"
+	_StepStatusName_4 = "SkippedDueToPreErr"
+)
+
+var (
+	_StepStatusIndex_0 = [...]uint8{0, 7, 11}
+	_StepStatusIndex_1 = [...]uint8{0, 2}
+	_StepStatusIndex_2 = [...]uint8{0, 3}
+	_StepStatusIndex_3 = [...]uint8{0, 20}
+	_StepStatusIndex_4 = [...]uint8{0, 18}
+)
+
+func (i StepStatus) String() string {
+	switch {
+	case 1 <= i && i <= 2:
+		i -= 1
+		return _StepStatusName_0[_StepStatusIndex_0[i]:_StepStatusIndex_0[i+1]]
+	case i == 4:
+		return _StepStatusName_1
+	case i == 8:
+		return _StepStatusName_2
+	case i == 16:
+		return _StepStatusName_3
+	case i == 32:
+		return _StepStatusName_4
+	default:
+		return fmt.Sprintf("StepStatus(%d)", i)
+	}
+}
+
+var _StepStatusValues = []StepStatus{1, 2, 4, 8, 16, 32}
+
+var _StepStatusNameToValueMap = map[string]StepStatus{
+	_StepStatusName_0[0:7]:  1,
+	_StepStatusName_0[7:11]: 2,
+	_StepStatusName_1[0:2]:  4,
+	_StepStatusName_2[0:3]:  8,
+	_StepStatusName_3[0:20]: 16,
+	_StepStatusName_4[0:18]: 32,
+}
+
+// StepStatusString retrieves an enum value from the enum constants string name.
+// Throws an error if the param is not part of the enum.
+func StepStatusString(s string) (StepStatus, error) {
+	if val, ok := _StepStatusNameToValueMap[s]; ok {
+		return val, nil
+	}
+	return 0, fmt.Errorf("%s does not belong to StepStatus values", s)
+}
+
+// StepStatusValues returns all values of the enum
+func StepStatusValues() []StepStatus {
+	return _StepStatusValues
+}
+
+// IsAStepStatus returns "true" if the value is listed in the enum definition. "false" otherwise
+func (i StepStatus) IsAStepStatus() bool {
+	for _, v := range _StepStatusValues {
+		if i == v {
+			return true
+		}
+	}
+	return false
+}

daemon/hooks/test/test-error.sh

@@ -0,0 +1,5 @@
+#!/bin/sh -eu
+
+>&2 echo "TEST ERROR $ZREPL_HOOKTYPE $ZREPL_FS@$ZREPL_SNAPNAME"
+
+exit 1

daemon/hooks/test/test-large-stdout.sh

@@ -0,0 +1,18 @@
+#!/bin/sh -eu
+
+# Exceed default hook log size of 1<<20 bytes by double
+# The Go test should fail if buffer size exceeds 1MB
+
+pre_testing() {
+	ln=0
+	while :; do printf '%06d: 012345678901234567890123456789012345678901234567890123456789012345678901\n' "$ln"; ln="$(($ln + 1))"; done \
+	| head -c$(( 2 << 20 ))
+}
+
+case "$ZREPL_HOOKTYPE" in
+	pre_testing)
+		"$ZREPL_HOOKTYPE";;
+	*)
+		# Not handled by this script
+		exit 0;;
+esac

daemon/hooks/test/test-post-error.sh

@@ -0,0 +1,15 @@
+#!/bin/sh -eu
+
+post_testing() {
+	>&2 echo "TEST ERROR $ZREPL_HOOKTYPE $ZREPL_FS@$ZREPL_SNAPNAME"
+
+	exit 1
+}
+
+case "$ZREPL_HOOKTYPE" in
+	post_testing)
+		"$ZREPL_HOOKTYPE";;
+	*)
+		# Not handled by this script
+		exit 0;;
+esac

daemon/hooks/test/test-pre-error-post-ok.sh

@@ -0,0 +1,11 @@
+#!/bin/sh -eu
+
+if [ "$ZREPL_HOOKTYPE" = "pre_testing" ]; then
+	>&2 echo "TEST ERROR $ZREPL_HOOKTYPE $ZREPL_FS@$ZREPL_SNAPNAME"
+	exit 1
+elif [ "$ZREPL_HOOKTYPE" = "post_testing" ]; then
+	echo "TEST $ZREPL_HOOKTYPE $ZREPL_FS@$ZREPL_SNAPNAME"
+else
+	printf "Unknown hook type: %s" "$ZREPL_HOOKTYPE" 
+	exit 255
+fi

daemon/hooks/test/test-report-env.sh

@@ -0,0 +1,3 @@
+#!/bin/sh -eu
+
+echo "TEST $ZREPL_HOOKTYPE $ZREPL_FS@$ZREPL_SNAPNAME ${ZREPL_DRYRUN:+(dry run)}"

daemon/hooks/test/test-timeout.sh

@@ -0,0 +1,5 @@
+#!/bin/sh -eu
+
+echo "TEST $ZREPL_HOOKTYPE $ZREPL_FS@$ZREPL_SNAPNAME ZREPL_TIMEOUT=$ZREPL_TIMEOUT"
+
+exec sleep $(($ZREPL_TIMEOUT + 1))

daemon/logging/build_logging.go

@@ -11,6 +11,7 @@ import (
 	"github.com/pkg/errors"
 
 	"github.com/zrepl/zrepl/config"
+	"github.com/zrepl/zrepl/daemon/hooks"
 	"github.com/zrepl/zrepl/daemon/pruner"
 	"github.com/zrepl/zrepl/daemon/snapper"
 	"github.com/zrepl/zrepl/endpoint"
@@ -72,6 +73,7 @@ const (
 	SubsyEndpoint      Subsystem = "endpoint"
 	SubsysPruning      Subsystem = "pruning"
 	SubsysSnapshot     Subsystem = "snapshot"
+	SubsysHooks        Subsystem = "hook"
 	SubsysTransport    Subsystem = "transport"
 	SubsysTransportMux Subsystem = "transportmux"
 	SubsysRPC          Subsystem = "rpc"
@@ -85,6 +87,7 @@ func WithSubsystemLoggers(ctx context.Context, log logger.Logger) context.Contex
 	ctx = endpoint.WithLogger(ctx, log.WithField(SubsysField, SubsyEndpoint))
 	ctx = pruner.WithLogger(ctx, log.WithField(SubsysField, SubsysPruning))
 	ctx = snapper.WithLogger(ctx, log.WithField(SubsysField, SubsysSnapshot))
+	ctx = hooks.WithLogger(ctx, log.WithField(SubsysField, SubsysHooks))
 	ctx = transport.WithLogger(ctx, log.WithField(SubsysField, SubsysTransport))
 	ctx = transportmux.WithLogger(ctx, log.WithField(SubsysField, SubsysTransportMux))
 	ctx = rpc.WithLoggers(ctx,

daemon/snapper/snapper.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/zrepl/zrepl/config"
 	"github.com/zrepl/zrepl/daemon/filters"
+	"github.com/zrepl/zrepl/daemon/hooks"
 	"github.com/zrepl/zrepl/logger"
 	"github.com/zrepl/zrepl/zfs"
 )
@@ -35,8 +36,8 @@ type snapProgress struct {
 	// SnapDone
 	doneAt time.Time
 
-	// SnapErr
-	err error
+	// SnapErr TODO disambiguate state
+	runResults hooks.PlanReport
 }
 
 type args struct {
@@ -46,6 +47,8 @@ type args struct {
 	interval       time.Duration
 	fsf            *filters.DatasetMapFilter
 	snapshotsTaken chan<- struct{}
+	hooks          *hooks.List
+	dryRun         bool
 }
 
 type Snapper struct {
@@ -123,10 +126,16 @@ func PeriodicFromConfig(g *config.Global, fsf *filters.DatasetMapFilter, in *con
 		return nil, errors.New("interval must be positive")
 	}
 
+	hookList, err := hooks.ListFromConfig(&in.Hooks)
+	if err != nil {
+		return nil, errors.Wrap(err, "hook config error")
+	}
+
 	args := args{
 		prefix:   in.Prefix,
 		interval: in.Interval,
 		fsf:      fsf,
+		hooks:    hookList,
 		// ctx and log is set in Run()
 	}
 
@@ -141,6 +150,7 @@ func (s *Snapper) Run(ctx context.Context, snapshotsTaken chan<- struct{}) {
 	s.args.snapshotsTaken = snapshotsTaken
 	s.args.ctx = ctx
 	s.args.log = getLogger(ctx)
+	s.args.dryRun = false // for future expansion
 
 	u := func(u func(*Snapper)) State {
 		s.mtx.Lock()
@@ -241,7 +251,12 @@ func snapshot(a args, u updater) state {
 		plan = snapper.plan
 	})
 
-	hadErr := false
+	hookMatchCount := make(map[hooks.Hook]int, len(*a.hooks))
+	for _, h := range *a.hooks {
+		hookMatchCount[h] = 0
+	}
+
+	anyFsHadErr := false
 	// TODO channel programs -> allow a little jitter?
 	for fs, progress := range plan {
 		suffix := time.Now().In(time.UTC).Format("20060102_150405_000")
@@ -257,21 +272,68 @@ func snapshot(a args, u updater) state {
 			progress.state = SnapStarted
 		})
 
-		l.Debug("create snapshot")
-		err := zfs.ZFSSnapshot(fs, snapname, false)
-		if err != nil {
-			hadErr = true
-			l.WithError(err).Error("cannot create snapshot")
-		}
-		doneAt := time.Now()
+		var doneAt time.Time
 
+		hookEnvExtra := hooks.Env{
+			hooks.EnvFS:       fs.ToString(),
+			hooks.EnvSnapshot: snapname,
+		}
+
+		jobCallback := hooks.NewCallbackHookForFilesystem("snapshot", fs, func(_ context.Context) (err error) {
+			l.Debug("create snapshot")
+			err = zfs.ZFSSnapshot(fs, snapname, false) // TODO propagagte context to ZFSSnapshot
+			if err != nil {
+				l.WithError(err).Error("cannot create snapshot")
+			}
+			doneAt = time.Now()
+			return
+		})
+
+		fsHadErr := false
+		var planReport hooks.PlanReport
+		var plan *hooks.Plan
+		{
+			filteredHooks, err := a.hooks.CopyFilteredForFilesystem(fs)
+			if err != nil {
+				l.WithError(err).Error("unexpected filter error")
+				fsHadErr = true
+				goto updateFSState
+			}
+			// account for running hooks
+			for _, h := range filteredHooks {
+				hookMatchCount[h] = hookMatchCount[h] + 1
+			}
+
+			var planErr error
+			plan, planErr = hooks.NewPlan(&filteredHooks, hooks.PhaseSnapshot, jobCallback, hookEnvExtra)
+			if planErr != nil {
+				fsHadErr = true
+				l.WithError(planErr).Error("cannot create job hook plan")
+				goto updateFSState
+			}
+		}
+		{
+			l := hooks.GetLogger(a.ctx).WithField("fs", fs.ToString()).WithField("snap", snapname)
+			l.WithField("report", plan.Report().String()).Debug("begin run job plan")
+			plan.Run(hooks.WithLogger(a.ctx, l), a.dryRun)
+			planReport = plan.Report()
+			fsHadErr = planReport.HadError() // not just fatal errors
+			if fsHadErr {
+				l.WithField("report", planReport.String()).Error("end run job plan with error")
+			} else {
+				l.WithField("report", planReport.String()).Info("end run job plan successful")
+			}
+		}
+
+	updateFSState:
+		anyFsHadErr = anyFsHadErr || fsHadErr
 		u(func(snapper *Snapper) {
 			progress.doneAt = doneAt
 			progress.state = SnapDone
-			if err != nil {
+			if fsHadErr {
 				progress.state = SnapError
-				progress.err = err
 			}
+			progress.runResults = planReport
 		})
 	}
 
@@ -283,8 +345,21 @@ func snapshot(a args, u updater) state {
 		}
 	}
 
+	for h, mc := range hookMatchCount {
+		if mc == 0 {
+			hookIdx := -1
+			for idx, ah := range *a.hooks {
+				if ah == h {
+					hookIdx = idx
+					break
+				}
+			}
+			a.log.WithField("hook", h.String()).WithField("hook_number", hookIdx+1).Warn("hook did not match any snapshotted filesystems")
+		}
+	}
+
 	return u(func(snapper *Snapper) {
-		if hadErr {
+		if anyFsHadErr {
 			snapper.state = ErrorWait
 			snapper.err = errors.New("one or more snapshots could not be created, check logs for details")
 		} else {

docs/changelog.rst

@@ -32,6 +32,9 @@ We use the following annotations for classifying changes:
 * Go modules for dependency management both inside and outside of GOPATH
   (``lazy.sh`` and ``Makefile`` force ``GO111MODULE=on``)
 * |feature| Use ``zfs destroy pool/fs@snap1,snap2,...`` CLI feature if available
+* |feature| :ref:`Pre- and Post-Snapshot Hooks <job-snapshotting-hooks>`
+  with built-in support for MySQL and Postgres checkpointing
+  as well as custom scripts
 
 0.1.1
 -----

docs/configuration.rst

@@ -7,10 +7,11 @@ Configuration
 
 .. toctree::
 
-    configuration/preface
+    configuration/overview
     configuration/jobs
     configuration/transports
     configuration/filter_syntax
+    configuration/snapshotting
     configuration/prune
     configuration/logging
     configuration/monitoring

docs/configuration/jobs.rst

@@ -1,222 +1,9 @@
 .. include:: ../global.rst.inc
 
-.. |serve-transport| replace:: :ref:`serve specification<transport>`
-.. |connect-transport| replace:: :ref:`connect specification<transport>`
-.. |snapshotting-spec| replace:: :ref:`snapshotting specification <job-snapshotting-spec>`
-.. |pruning-spec| replace:: :ref:`pruning specification <prune>`
-.. |filter-spec| replace:: :ref:`filter specification<pattern-filter>`
-
 .. _job:
 
-Job Types & Replication
-=======================
-
-.. _job-overview:
-
-Overview & Terminology
-----------------------
-
-A *job* is the unit of activity tracked by the zrepl daemon.
-Every job has a unique ``name``, a ``type`` and type-dependent fields which are documented on this page.
-
-Replication always happens between a pair of jobs: one is the **active side**, and one the **passive side**.
-The active side executes the replication logic whereas the passive side responds to requests after checking the active side's permissions.
-For communication, the active side connects to the passive side using a :ref:`transport <transport>` and starts issuing remote procedure calls (RPCs).
-
-The following table shows how different job types can be combined to achieve both push and pull mode setups:
-
-+-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
-| Setup name            | active side  | passive side                     | use case                                                                           |
-+=======================+==============+==================================+====================================================================================+
-| Push mode             | ``push``     | ``sink``                         | * Laptop backup                                                                    |
-|                       |              |                                  | * NAS behind NAT to offsite                                                        |
-+-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
-| Pull mode             | ``pull``     | ``source``                       | * Central backup-server for many nodes                                             |
-|                       |              |                                  | * Remote server to NAS behind NAT                                                  |
-+-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
-| Local replication     | | ``push`` + ``sink`` in one config             | * Backup FreeBSD boot pool                                                         |
-|                       | | with :ref:`local transport <transport-local>` |                                                                                    |
-+-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
-| Snap & prune-only     | ``snap``     | N/A                              | * | Snapshots & pruning but no replication                                         |
-|                       |              |                                  |   | required                                                                       |
-|                       |              |                                  | * Workaround for :ref:`source-side pruning <prune-workaround-source-side-pruning>` |
-+-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
-
-How the Active Side Works
-~~~~~~~~~~~~~~~~~~~~~~~~~
-
-The active side (:ref:`push <job-push>` and :ref:`pull <job-pull>` job) executes the replication and pruning logic:
-
-* Wakeup because of finished snapshotting (``push`` job) or pull interval ticker (``pull`` job).
-* Connect to the corresponding passive side using a :ref:`transport <transport>` and instantiate an RPC client.
-* Replicate data from the sending to the receiving side.
-* Prune on sender & receiver.
-
-.. TIP::
-  The progress of the active side can be watched live using the ``zrepl status`` subcommand.
-
-How the Passive Side Works
-~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-The passive side (:ref:`sink <job-sink>` and :ref:`source <job-source>`) waits for connections from the corresponding active side,
-using the transport listener type specified in the ``serve`` field of the job configuration.
-Each transport listener provides a client's identity to the passive side job.
-It uses the client identity for access control:
-
-* The ``sink`` job maps requests from different client identities to their respective sub-filesystem tree ``root_fs/${client_identity}``.
-* The ``source`` job has a whitelist of client identities that are allowed pull access.
-
-.. TIP::
-   The implementation of the ``sink`` job requires that the connecting client identities be a valid ZFS filesystem name components.
-
-How Replication Works
-~~~~~~~~~~~~~~~~~~~~~
-
-One of the major design goals of the replication module is to avoid any duplication of the nontrivial logic.
-As such, the code works on abstract senders and receiver **endpoints**, where typically one will be implemented by a local program object and the other is an RPC client instance.
-Regardless of push- or pull-style setup, the logic executes on the active side, i.e. in the ``push`` or ``pull`` job.
-
-The following steps take place during replication and can be monitored using the ``zrepl status`` subcommand:
-
-* Plan the replication:
-
-  * Compare sender and receiver filesystem snapshots
-  * Build the **replication plan**
-
-    * Per filesystem, compute a diff between sender and receiver snapshots
-    * Build a list of replication steps
-
-      * If possible, use incremental sends (``zfs send -i``)
-      * Otherwise, use full send of most recent snapshot on sender
-      * Give up on filesystems that cannot be replicated without data loss
-
-  * Retry on errors that are likely temporary (i.e. network failures).
-  * Give up on filesystems where a permanent error was received over RPC.
-
-* Execute the plan
-
-  * Perform replication steps in the following order:
-    Among all filesystems with pending replication steps, pick the filesystem whose next replication step's snapshot is the oldest.
-  * Create placeholder filesystems on the receiving side to mirror the dataset paths on the sender to ``root_fs/${client_identity}``.
-  * After a successful replication step, update the replication cursor bookmark (see below).
-   
-The idea behind the execution order of replication steps is that if the sender snapshots all filesystems simultaneously at fixed intervals, the receiver will have all filesystems snapshotted at time ``T1`` before the first snapshot at ``T2 = T1 + $interval`` is replicated.
-
-.. _replication-cursor-bookmark:
-
-The **replication cursor bookmark** ``#zrepl_replication_cursor`` is kept per filesystem on the sending side of a replication setup:
-It is a bookmark of the most recent successfully replicated snapshot to the receiving side.
-It is is used by the :ref:`not_replicated <prune-keep-not-replicated>` keep rule to identify all snapshots that have not yet been replicated to the receiving side.
-Regardless of whether that keep rule is used, the bookmark ensures that replication can always continue incrementally.
-Note that there is only one cursor bookmark per filesystem, which prohibits multiple jobs to replicate the same filesystem (:ref:`see below<jobs-multiple-jobs>`).
-
-.. _replication-placeholder-property:
-
-**Placeholder filesystems** on the receiving side are regular ZFS filesystems with the placeholder property ``zrepl:placeholder=on``.
-Placeholders allow the receiving side to mirror the sender's ZFS dataset hierachy without replicating every filesystem at every intermediary dataset path component.
-Consider the following example: ``S/H/J`` shall be replicated to ``R/sink/job/S/H/J``, but neither ``S/H`` nor ``S`` shall be replicated.
-ZFS requires the existence of ``R/sink/job/S`` and ``R/sink/job/S/H`` in order to receive into ``R/sink/job/S/H/J``.
-Thus, zrepl creates the parent filesystems as placeholders on the receiving side.
-If at some point ``S/H`` and ``S`` shall be replicated, the receiving side invalidates the placeholder flag automatically.
-The ``zrepl test placeholder`` command can be used to check whether a filesystem is a placeholder.
-
-.. ATTENTION::
-
-    Currently, zrepl does not replicate filesystem properties.
-    Whe receiving a filesystem, it is never mounted (`-u` flag)  and `mountpoint=none` is set.
-    This is temporary and being worked on :issue:`24`.
-
-
-.. _job-snapshotting-spec:
-
-Taking Snaphots
----------------
-
-The ``push``, ``source`` and ``snap`` jobs can automatically take periodic snapshots of the filesystems matched by the ``filesystems`` filter field.
-The snapshot names are composed of a user-defined prefix followed by a UTC date formatted like ``20060102_150405_000``.
-We use UTC because it will avoid name conflicts when switching time zones or between summer and winter time.
-
-For ``push`` jobs, replication is automatically triggered after all filesystems have been snapshotted.
-
-::
-
-    jobs:
-    - type: push
-      filesystems: {
-        "<": true,
-        "tmp": false
-      }
-      snapshotting:
-        type: periodic
-        prefix: zrepl_
-        interval: 10m
-      ...
-
-There is also a ``manual`` snapshotting type, which covers the following use cases:
-
-* Existing infrastructure for automatic snapshots: you only want to use this zrepl job for replication.
-* Run scripts before and after taking snapshots (like locking database tables).
-  We are working on better integration for this use case: see :issue:`74`.
-* Handling snapshotting through a separate ``snap`` job.
-
-Note that you will have to trigger replication manually using the ``zrepl signal wakeup JOB`` subcommand in that case.
-
-::
-
-   jobs:
-   - type: push
-     filesystems: {
-       "<": true,
-       "tmp": false
-     }
-     snapshotting:
-       type: manual
-     ...
-
-.. _jobs-multiple-jobs:
-
-Multiple Jobs & More than 2 Machines
-------------------------------------
-
-.. ATTENTION::
-
-  When using multiple jobs across single or multiple machines, the following rules are critical to avoid race conditions & data loss:
-
-  1. The sets of ZFS filesystems matched by the ``filesystems`` filter fields must be disjoint across all jobs configured on a machine.
-  2. The ZFS filesystem subtrees of jobs with ``root_fs`` must be disjoint.
-  3. Across all zrepl instances on all machines in the replication domain, there must be a 1:1 correspondence between active and passive jobs.
-
-  Explanations & exceptions to above rules are detailed below.
-
-If you would like to see improvements to multi-job setups, please `open an issue on GitHub <https://github.com/zrepl/zrepl/issues/new>`_.
-
-No Overlapping
-~~~~~~~~~~~~~~
-
-Jobs run independently of each other.
-If two jobs match the same filesystem with their ``filesystems`` filter, they will operate on that filesystem independently and potentially in parallel.
-For example, if job A prunes snapshots that job B is planning to replicate, the replication will fail because B asssumed the snapshot to still be present.
-More subtle race conditions can occur with the :ref:`replication cursor bookmark <replication-cursor-bookmark>`, which currently only exists once per filesystem.
-
-N push jobs to 1 sink
-~~~~~~~~~~~~~~~~~~~~~
-
-The :ref:`sink job <job-sink>` namespaces by client identity.
-It is thus safe to push to one sink job with different client identities.
-If the push jobs have the same client identity, the filesystems matched by the push jobs must be disjoint to avoid races.
-
-N pull jobs from 1 source
-~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Multiple pull jobs pulling from the same source have potential for race conditions during pruning:
-each pull job prunes the source side independently, causing replication-prune and prune-prune races.
-
-There is currently no way for a pull job to filter which snapshots it should attempt to replicate.
-Thus, it is not possibe to just manually assert that the prune rules of all pull jobs are disjoint to avoid replication-prune and prune-prune races.
-
-
-------------------------------------------------------------------------------
-
+Job Types in Detail
+===================
 
 .. _job-push:
 

docs/configuration/misc.rst

@@ -6,16 +6,16 @@ Miscellaneous
 Runtime Directories & UNIX Sockets
 ----------------------------------
 
-zrepl daemon creates various UNIX sockets to allow communicating with it:
+The zrepl daemon needs to open various UNIX sockets in a runtime directory:
 
-* the :ref:`transport-ssh+stdinserver` transport connects to a socket named after ``client_identity`` parameter
-* the ``control`` CLI subcommand connects to a defined control socket
+* a ``control`` socket that the CLI commands use to interact with the daemon
+* the :ref:`transport-ssh+stdinserver` listener opens one socket per configured client, named after ``client_identity`` parameter
 
-There is no further authentication on these sockets.
-Therefore we have to make sure they can only be created and accessed by ``zrepl daemon``.
-In fact, ``zrepl daemon`` will not bind a socket to a path in a directory that is world-accessible.
+There is no authentication on these sockets except the UNIX permissions.
+The zrepl daemon will refuse to bind any of the above sockets in a directory that is world-accessible.
 
-The directories can be configured in the main configuration file, the defaults are provided below:
+The following sections of the ``global`` config shows the default paths.
+The shell script below shows how the default runtime directory can be created.
 
 ::
 
@@ -27,6 +27,12 @@ The directories can be configured in the main configuration file, the defaults a
           sockdir: /var/run/zrepl/stdinserver
 
 
+::
+
+    mkdir -p /var/run/zrepl/stdinserver
+    chmod -R 0700 /var/run/zrepl
+
+
 Durations & Intervals
 ---------------------
 

docs/configuration/overview.rst

@@ -0,0 +1,191 @@
+
+Overview & Terminology
+======================
+
+All work zrepl does is performed by the zrepl daemon which is configured in a single YAML configuration file loaded on startup.
+The following paths are considered:
+
+* If set, the location specified via the global ``--config`` flag
+* ``/etc/zrepl/zrepl.yml``
+* ``/usr/local/etc/zrepl/zrepl.yml``
+
+The ``zrepl configcheck`` subcommand can be used to validate the configuration.
+The command will output nothing and exit with zero status code if the configuration is valid.
+The error messages vary in quality and usefulness: please report confusing config errors to the tracking :issue:`155`.
+Full example configs such as in the :ref:`tutorial` or the :sampleconf:`/` directory might also be helpful.
+However, copy-pasting examples is no substitute for reading documentation!
+
+Config File Structure
+---------------------
+
+.. code-block:: yaml
+
+   global: ...
+   jobs:
+   - name: backup
+     type: push
+   - ...
+
+zrepl is confgured using a single YAML configuration file with two main sections: ``global`` and ``jobs``.
+The ``global`` section is filled with sensible defaults and is covered later in this chapter.
+The ``jobs`` section is a list of jobs which we are goind to explain now.
+
+.. _job-overview:
+
+Jobs \& How They Work Together
+------------------------------
+
+A *job* is the unit of activity tracked by the zrepl daemon.
+The ``type`` of a job determines its role in a replication setup and in snapshot management.
+Jobs are identified by their ``name``, both in log files and the ``zrepl status`` command.
+
+Replication always happens between a pair of jobs: one is the **active side**, and one the **passive side**.
+The active side connects to the passive side using a :ref:`transport <transport>` and starts executing the replication logic.
+The passive side responds to requests from the active side after checking its persmissions.
+
+The following table shows how different job types can be combined to achieve **both push and pull mode setups**.
+Note that snapshot-creation denoted by "(snap)" is orthogonal to whether a job is active or passive.
+
++-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
+| Setup name            | active side  | passive side                     | use case                                                                           |
++=======================+==============+==================================+====================================================================================+
+| Push mode             | ``push``     | ``sink``                         | * Laptop backup                                                                    |
+|                       | (snap)       |                                  | * NAS behind NAT to offsite                                                        |
++-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
+| Pull mode             | ``pull``     | ``source``                       | * Central backup-server for many nodes                                             |
+|                       |              | (snap)                           | * Remote server to NAS behind NAT                                                  |
++-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
+| Local replication     | | ``push`` + ``sink`` in one config             | * Backup FreeBSD boot pool                                                         |
+|                       | | with :ref:`local transport <transport-local>` |                                                                                    |
++-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
+| Snap & prune-only     | ``snap``     | N/A                              | * | Snapshots & pruning but no replication                                         |
+|                       | (snap)       |                                  |   | required                                                                       |
+|                       |              |                                  | * Workaround for :ref:`source-side pruning <prune-workaround-source-side-pruning>` |
++-----------------------+--------------+----------------------------------+------------------------------------------------------------------------------------+
+
+How the Active Side Works
+-------------------------
+
+The active side (:ref:`push <job-push>` and :ref:`pull <job-pull>` job) executes the replication and pruning logic:
+
+* Wakeup because of finished snapshotting (``push`` job) or pull interval ticker (``pull`` job).
+* Connect to the corresponding passive side using a :ref:`transport <transport>` and instantiate an RPC client.
+* Replicate data from the sending to the receiving side (see below).
+* Prune on sender & receiver.
+
+.. TIP::
+  The progress of the active side can be watched live using the ``zrepl status`` subcommand.
+
+How the Passive Side Works
+--------------------------
+
+The passive side (:ref:`sink <job-sink>` and :ref:`source <job-source>`) waits for connections from the corresponding active side,
+using the transport listener type specified in the ``serve`` field of the job configuration.
+Each transport listener provides a client's identity to the passive side job.
+It uses the client identity for access control:
+
+* The ``sink`` job maps requests from different client identities to their respective sub-filesystem tree ``root_fs/${client_identity}``.
+* The ``source`` job has a whitelist of client identities that are allowed pull access.
+
+.. TIP::
+   The implementation of the ``sink`` job requires that the connecting client identities be a valid ZFS filesystem name components.
+
+How Replication Works
+---------------------
+
+One of the major design goals of the replication module is to avoid any duplication of the nontrivial logic.
+As such, the code works on abstract senders and receiver **endpoints**, where typically one will be implemented by a local program object and the other is an RPC client instance.
+Regardless of push- or pull-style setup, the logic executes on the active side, i.e. in the ``push`` or ``pull`` job.
+
+The following steps take place during replication and can be monitored using the ``zrepl status`` subcommand:
+
+* Plan the replication:
+
+  * Compare sender and receiver filesystem snapshots
+  * Build the **replication plan**
+
+    * Per filesystem, compute a diff between sender and receiver snapshots
+    * Build a list of replication steps
+
+      * If possible, use incremental sends (``zfs send -i``)
+      * Otherwise, use full send of most recent snapshot on sender
+      * Give up on filesystems that cannot be replicated without data loss
+
+  * Retry on errors that are likely temporary (i.e. network failures).
+  * Give up on filesystems where a permanent error was received over RPC.
+
+* Execute the plan
+
+  * Perform replication steps in the following order:
+    Among all filesystems with pending replication steps, pick the filesystem whose next replication step's snapshot is the oldest.
+  * Create placeholder filesystems on the receiving side to mirror the dataset paths on the sender to ``root_fs/${client_identity}``.
+  * After a successful replication step, update the replication cursor bookmark (see below).
+   
+The idea behind the execution order of replication steps is that if the sender snapshots all filesystems simultaneously at fixed intervals, the receiver will have all filesystems snapshotted at time ``T1`` before the first snapshot at ``T2 = T1 + $interval`` is replicated.
+
+.. _replication-cursor-bookmark:
+
+The **replication cursor bookmark** ``#zrepl_replication_cursor`` is kept per filesystem on the sending side of a replication setup:
+It is a bookmark of the most recent successfully replicated snapshot to the receiving side.
+It is is used by the :ref:`not_replicated <prune-keep-not-replicated>` keep rule to identify all snapshots that have not yet been replicated to the receiving side.
+Regardless of whether that keep rule is used, the bookmark ensures that replication can always continue incrementally.
+Note that there is only one cursor bookmark per filesystem, which prohibits multiple jobs to replicate the same filesystem (:ref:`see below<jobs-multiple-jobs>`).
+
+.. _replication-placeholder-property:
+
+**Placeholder filesystems** on the receiving side are regular ZFS filesystems with the placeholder property ``zrepl:placeholder=on``.
+Placeholders allow the receiving side to mirror the sender's ZFS dataset hierachy without replicating every filesystem at every intermediary dataset path component.
+Consider the following example: ``S/H/J`` shall be replicated to ``R/sink/job/S/H/J``, but neither ``S/H`` nor ``S`` shall be replicated.
+ZFS requires the existence of ``R/sink/job/S`` and ``R/sink/job/S/H`` in order to receive into ``R/sink/job/S/H/J``.
+Thus, zrepl creates the parent filesystems as placeholders on the receiving side.
+If at some point ``S/H`` and ``S`` shall be replicated, the receiving side invalidates the placeholder flag automatically.
+The ``zrepl test placeholder`` command can be used to check whether a filesystem is a placeholder.
+
+.. ATTENTION::
+
+    Currently, zrepl does not replicate filesystem properties.
+    Whe receiving a filesystem, it is never mounted (`-u` flag)  and `mountpoint=none` is set.
+    This is temporary and being worked on :issue:`24`.
+
+
+.. _jobs-multiple-jobs:
+
+Multiple Jobs & More than 2 Machines
+------------------------------------
+
+.. ATTENTION::
+
+  When using multiple jobs across single or multiple machines, the following rules are critical to avoid race conditions & data loss:
+
+  1. The sets of ZFS filesystems matched by the ``filesystems`` filter fields must be disjoint across all jobs configured on a machine.
+  2. The ZFS filesystem subtrees of jobs with ``root_fs`` must be disjoint.
+  3. Across all zrepl instances on all machines in the replication domain, there must be a 1:1 correspondence between active and passive jobs.
+
+  Explanations & exceptions to above rules are detailed below.
+
+If you would like to see improvements to multi-job setups, please `open an issue on GitHub <https://github.com/zrepl/zrepl/issues/new>`_.
+
+No Overlapping
+~~~~~~~~~~~~~~
+
+Jobs run independently of each other.
+If two jobs match the same filesystem with their ``filesystems`` filter, they will operate on that filesystem independently and potentially in parallel.
+For example, if job A prunes snapshots that job B is planning to replicate, the replication will fail because B asssumed the snapshot to still be present.
+More subtle race conditions can occur with the :ref:`replication cursor bookmark <replication-cursor-bookmark>`, which currently only exists once per filesystem.
+
+N push jobs to 1 sink
+~~~~~~~~~~~~~~~~~~~~~
+
+The :ref:`sink job <job-sink>` namespaces by client identity.
+It is thus safe to push to one sink job with different client identities.
+If the push jobs have the same client identity, the filesystems matched by the push jobs must be disjoint to avoid races.
+
+N pull jobs from 1 source
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Multiple pull jobs pulling from the same source have potential for race conditions during pruning:
+each pull job prunes the source side independently, causing replication-prune and prune-prune races.
+
+There is currently no way for a pull job to filter which snapshots it should attempt to replicate.
+Thus, it is not possibe to just manually assert that the prune rules of all pull jobs are disjoint to avoid replication-prune and prune-prune races.
+

docs/configuration/preface.rst

@@ -1,39 +0,0 @@
-
-.. _configuration_preface:
-
-=======
-Preface
-=======
-
------------------------
-Configuration File Path
------------------------
-
-zrepl searches for its main configuration file in the following locations (in that order):
-
-* If set, the location specified via the global ``--config`` flag
-* ``/etc/zrepl/zrepl.yml``
-* ``/usr/local/etc/zrepl/zrepl.yml``
-
-The examples in the :ref:`tutorial` or the :sampleconf:`/` directory should provide a good starting point.
-
--------------------
-Runtime Directories
--------------------
-
-zrepl requires runtime directories for various UNIX sockets --- they are documented in the :ref:`config file<conf-runtime-directories>`.
-Your package maintainer / init script should take care of creating them.
-Alternatively, for default settings, the following should to the trick.
-
-::
-
-    mkdir -p /var/run/zrepl/stdinserver
-    chmod -R 0700 /var/run/zrepl
-
-
-----------
-Validating
-----------
-
-The config can be validated using the ``zrepl configcheck`` subcommand.
-

docs/configuration/snapshotting.rst

@@ -0,0 +1,192 @@
+.. include:: ../global.rst.inc
+
+.. _job-snapshotting-spec:
+
+Taking Snaphots
+===============
+
+The ``push``, ``source`` and ``snap`` jobs can automatically take periodic snapshots of the filesystems matched by the ``filesystems`` filter field.
+The snapshot names are composed of a user-defined prefix followed by a UTC date formatted like ``20060102_150405_000``.
+We use UTC because it will avoid name conflicts when switching time zones or between summer and winter time.
+
+For ``push`` jobs, replication is automatically triggered after all filesystems have been snapshotted.
+
+::
+
+    jobs:
+    - type: push
+      filesystems: {
+        "<": true,
+        "tmp": false
+      }
+      snapshotting:
+        type: periodic
+        prefix: zrepl_
+        interval: 10m
+        hooks: ...
+      ...
+
+There is also a ``manual`` snapshotting type, which covers the following use cases:
+
+* Existing infrastructure for automatic snapshots: you only want to use this zrepl job for replication.
+* Handling snapshotting through a separate ``snap`` job.
+
+Note that you will have to trigger replication manually using the ``zrepl signal wakeup JOB`` subcommand in that case.
+
+::
+
+   jobs:
+   - type: push
+     filesystems: {
+       "<": true,
+       "tmp": false
+     }
+     snapshotting:
+       type: manual
+     ...
+
+.. _job-snapshotting-hooks:
+
+Pre- and Post-Snapshot Hooks
+----------------------------
+
+Jobs with `periodic snapshots <job-snapshotting-spec_>`_ can run hooks before and/or after taking the snapshot specified in ``snapshotting.hooks``:
+Hooks are called per filesystem before and after the snapshot is taken (pre- and post-edge).
+Pre-edge invocations are in configuration order, post-edge invocations in reverse order, i.e. like a stack.
+If a pre-snapshot invocation fails, ``err_is_fatal=true`` cuts off subsequent hooks, does not take a snapshot, and only invokes post-edges corresponding to previous successful pre-edges.
+``err_is_fatal=false`` logs the failed pre-edge invocation but does not affect subsequent hooks nor snapshotting itself.
+Post-edges are only invoked for hooks whose pre-edges ran without error.
+Note that hook failures for one filesystem never affect other filesystems.
+
+The optional ``timeout`` parameter specifies a period after which zrepl will kill the hook process and report an error.
+The default is 30 seconds and may be specified in any units understood by `time.ParseDuration <https://golang.org/pkg/time/#ParseDuration>`_.
+
+The optional ``filesystems`` filter which limits the filesystems the hook runs for. This uses the same |filter-spec| as jobs.
+
+Most hook types take additional parameters, please refer to the respective subsections below.
+
+.. list-table::
+    :widths: 20 10 70
+    :header-rows: 1
+
+    * - Hook ``type``
+      - Details
+      - Description
+    * - ``command``
+      - :ref:`Details <job-hook-type-command>`
+      - Arbitrary pre- and post snapshot scripts.
+    * - ``postgres-checkpoint``
+      - :ref:`Details <job-hook-type-postgres-checkpoint>`
+      - Execute Postgres ``CHECKPOINT`` SQL command before snapshot.
+    * - ``mysql-lock-tables``
+      - :ref:`Details <job-hook-type-mysql-lock-tables>`
+      - Flush and read-Lock MySQL tables while taking the snapshot.
+      
+.. _job-hook-type-command:
+
+``command`` Hooks
+~~~~~~~~~~~~~~~~~
+
+::
+
+
+    jobs:
+    - type: push
+      filesystems: {
+        "<": true,
+        "tmp": false
+      }
+      snapshotting:
+        type: periodic
+        prefix: zrepl_
+        interval: 10m
+        hooks:
+        - type: command
+          path: /etc/zrepl/hooks/zrepl-notify.sh
+          timeout: 30s
+          err_is_fatal: false
+        - type: command
+          path: /etc/zrepl/hooks/special-snapshot.sh
+          filesystems: {
+            "tank/special": true
+          }
+      ...
+
+
+The hook type ``command`` is the only currently supported hook type.
+Future versions of zrepl may support other hook types.
+The ``path`` to the hook executables must be absolute (e.g. ``/etc/zrepl/hooks/zrepl-notify.sh``).
+No arguments may be specified; create a wrapper script if zrepl must call an executable that requires arguments.
+zrepl will call the hook both before and after the snapshot, but with different values of the ``ZREPL_HOOKTYPE`` environment variable; see below.
+The process standard output is logged at level INFO. Standard error is logged at level WARN.
+
+zrepl sets a number of environment variables for the hook processes:
+
+* ``ZREPL_HOOKTYPE``: either "pre_snapshot" or "post_snapshot"
+* ``ZREPL_FS``: the ZFS filesystem name being snapshotted
+* ``ZREPL_SNAPNAME``: the zrepl-generated snapshot name (e.g. ``zrepl_20380119_031407_000``)
+* ``ZREPL_DRYRUN``: set to ``"true"`` if a dry run is in progress so scripts can print, but not run, their commands
+
+An empty template hook can be found in :sampleconf:`hooks/template.sh`.
+
+.. _job-hook-type-postgres-checkpoint:
+
+``postgres-checkpoint`` Hook
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Connects to a Postgres server and executes the ``CHECKPOINT`` statement pre-snapshot.
+Checkpointing applies the WAL contents to all data files and syncs the data files to disk.
+This is not required for a consistent database backup: it merely forward-pays the "cost" of WAL replay to the time of snapshotting instead of at restore.
+However, the Postgres manual recommends against checkpointing during normal operation.
+Further, the operation requires Postgres superuser privileges.
+zrepl users must decide on their own whether this hook is useful for them (it likely isn't).
+
+.. ATTENTION::
+    Note that WALs and Postgres data directory (with all database data files) must be on the same filesystem to guarantee a correct point-in-time backup with the ZFS snapshot.
+
+DSN syntax documented here: `<https://godoc.org/github.com/lib/pq>`_
+
+.. code-block:: sql
+
+   CREATE USER zrepl_checkpoint PASSWORD yourpasswordhere;
+   ALTER ROLE zrepl_checkpoint SUPERUSER;
+
+.. code-block:: yaml
+
+  - type: postgres-checkpoint
+    dsn: "host=localhost port=5432 user=postgres password=yourpasswordhere sslmode=disable"
+    filesystems: {
+        "p1/postgres/data11": true
+    }
+
+.. _job-hook-type-mysql-lock-tables:
+
+``mysql-lock-tables`` Hook
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Connects to MySQL and executes
+
+* pre-snapshot ``FLUSH TABLES WITH READ LOCK`` to lock all tables in all databases in the MySQL server we connect to (`docs <https://dev.mysql.com/doc/refman/8.0/en/flush.html#flush-tables-with-read-lock>`_)
+* post-snapshot ``UNLOCK TABLES``  reverse above operation.
+
+Above procedure is documented in the `MySQL manual <https://dev.mysql.com/doc/mysql-backup-excerpt/5.7/en/backup-methods.html>`_
+as a means to produce a consistent backup of a MySQL DBMS installation (i.e., all databases).
+
+`DSN syntax <https://github.com/go-sql-driver/mysql#dsn-data-source-name>`_: ``[username[:password]@][protocol[(address)]]/dbname[?param1=value1&...&paramN=valueN]``
+
+.. ATTENTION::
+    All MySQL databases must be on the same ZFS filesystem to guarantee a consistent point-in-time backup with the ZFS snapshot.
+
+.. code-block:: sql
+
+   CREATE USER zrepl_lock_tables IDENTIFIED BY 'yourpasswordhere';
+   GRANT RELOAD ON *.* TO zrepl_lock_tables;
+   FLUSH PRIVILEGES;
+
+.. code-block:: yaml
+
+  - type: mysql-lock-tables
+    dsn: "zrepl_lock_tables:yourpasswordhere@tcp(localhost)/"
+    filesystems: {
+      "tank/mysql": true
+    }

docs/global.rst.inc

@@ -17,3 +17,10 @@
    :target: https://www.patreon.com/zrepl
 .. |Twitter| image:: https://img.shields.io/twitter/url/https/github.com/zrepl/zrepl.svg?style=social
    :target: https://twitter.com/intent/tweet?text=Wow:&url=https%3A%2F%2Fgithub.com%2Fzrepl%2Fzrepl
+
+
+.. |serve-transport| replace:: :ref:`serve specification<transport>`
+.. |connect-transport| replace:: :ref:`connect specification<transport>`
+.. |snapshotting-spec| replace:: :ref:`snapshotting specification <job-snapshotting-spec>`
+.. |pruning-spec| replace:: :ref:`pruning specification <prune>`
+.. |filter-spec| replace:: :ref:`filter specification<pattern-filter>`

docs/index.rst

@@ -64,6 +64,7 @@ Main Features
 * **Automatic snapshot management**
 
   * [x] Periodic filesystem snapshots
+  * [x] Support for pre- and post-snapshot hooks with builtins for MySQL & Postgres
   * [x] Flexible :ref:`pruning rule system <prune>`
 
     * [x] Age-based fading (grandfathering scheme)

docs/installation.rst

@@ -86,8 +86,7 @@ Either way, all build results are located in the ``artifacts/`` directory.
 What next?
 ----------
 
-Read the :ref:`configuration chapter<configuration_toc>` and optionally create the :ref:`runtime directories <configuration_preface>`.
-Afterwards, continue with the :ref:`usage chapter<usage>`.
+Read the :ref:`configuration chapter<configuration_toc>` and then continue with the :ref:`usage chapter<usage>`.
 
 **Reminder**: If you want a quick introduction, please read the :ref:`tutorial`.
 

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/gdamore/tcell v1.2.0
 	github.com/go-critic/go-critic v0.3.4 // indirect
 	github.com/go-logfmt/logfmt v0.3.0
+	github.com/go-sql-driver/mysql v1.4.1-0.20190907122137-b2c03bcae3d4
 	github.com/gogo/protobuf v1.2.1 // indirect
 	github.com/golang/mock v1.2.0 // indirect
 	github.com/golang/protobuf v1.2.0
@@ -29,6 +30,7 @@ require (
 	github.com/konsorten/go-windows-terminal-sequences v1.0.2 // indirect
 	github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515 // indirect
 	github.com/kr/pretty v0.1.0
+	github.com/lib/pq v1.2.0
 	github.com/mattn/go-isatty v0.0.3
 	github.com/matttproud/golang_protobuf_extensions v1.0.0 // indirect
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
@@ -47,7 +49,7 @@ require (
 	github.com/spf13/jwalterweatherman v1.1.0 // indirect
 	github.com/spf13/pflag v1.0.3
 	github.com/spf13/viper v1.3.2 // indirect
-	github.com/stretchr/testify v1.2.2
+	github.com/stretchr/testify v1.4.0
 	github.com/theckman/goconstraint v1.11.0 // indirect
 	github.com/yudai/gojsondiff v0.0.0-20170107030110-7b1b7adf999d
 	github.com/yudai/golcs v0.0.0-20170316035057-ecda9a501e82 // indirect

go.sum

@@ -16,6 +16,7 @@ github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDk
 github.com/coreos/etcd v3.3.10+incompatible/go.mod h1:uF7uidLiAD3TWHmW31ZFd/JWoc32PjwdhPthX9715RE=
 github.com/coreos/go-etcd v2.0.0+incompatible/go.mod h1:Jez6KQU2B/sWsbdaef3ED8NzMklzPG4d5KIOhIy30Tk=
 github.com/coreos/go-semver v0.2.0/go.mod h1:nnelYz7RCh+5ahJtPPxZlU+153eP4D4r3EedlOD2RNk=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/fatih/color v1.6.0/go.mod h1:Zm6kSWBoL9eyXnKyktHP6abPY2pDugNf5KwzbycvMj4=
@@ -38,6 +39,10 @@ github.com/go-lintpack/lintpack v0.5.2/go.mod h1:NwZuYi2nUHho8XEIZ6SIxihrnPoqBTD
 github.com/go-logfmt/logfmt v0.3.0 h1:8HUsc87TaSWLKwrnumgC8/YconD2fJQsRJAsWaPg2ic=
 github.com/go-logfmt/logfmt v0.3.0/go.mod h1:Qt1PoO58o5twSAckw1HlFXLmHsOX5/0LbT9GBnD5lWE=
 github.com/go-ole/go-ole v1.2.1/go.mod h1:7FAglXiTm7HKlQRDeOQ6ZNUHidzCWXuZWq/1dTyBNF8=
+github.com/go-sql-driver/mysql v1.4.1-0.20190907122137-b2c03bcae3d4 h1:0suja/iKSDbEIYLbrS/8C7iArJiWpgCNcR+zwAHu7Ig=
+github.com/go-sql-driver/mysql v1.4.1-0.20190907122137-b2c03bcae3d4/go.mod h1:zAC/RDZ24gD3HViQzih4MyKcchzm+sOG5ZlKdlhCg5w=
+github.com/go-sql-driver/mysql v1.4.1 h1:g24URVg0OFbNUTx9qqY1IRZ9D9z3iPyi5zKhQZpNwpA=
+github.com/go-sql-driver/mysql v1.4.1/go.mod h1:zAC/RDZ24gD3HViQzih4MyKcchzm+sOG5ZlKdlhCg5w=
 github.com/go-toolsmith/astcast v0.0.0-20181028201508-b7a89ed70af1/go.mod h1:TEo3Ghaj7PsZawQHxT/oBvo4HK/sl1RcuUHDKTTju+o=
 github.com/go-toolsmith/astcast v1.0.0 h1:JojxlmI6STnFVG9yOImLeGREv8W2ocNUM+iOhR6jE7g=
 github.com/go-toolsmith/astcast v1.0.0/go.mod h1:mt2OdQTeAQcY4DQgPSArJjHCcOwlX+Wl/kwN+LbLGQ4=
@@ -153,6 +158,8 @@ github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORN
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/lib/pq v1.2.0 h1:LXpIM/LZ5xGFhOpXAQUIMM1HdyqzVYM13zNdjCEEcA0=
+github.com/lib/pq v1.2.0/go.mod h1:5WUZQaWbwv1U+lTReE5YruASi9Al49XbQIvNi/34Woo=
 github.com/logrusorgru/aurora v0.0.0-20181002194514-a7b3b318ed4e/go.mod h1:7rIyQOR62GCctdiQpZ/zOJlFyk6y+94wXzv6RNZgaR4=
 github.com/lucasb-eyer/go-colorful v1.0.2 h1:mCMFu6PgSozg9tDNMMK3g18oJBX7oYGrC09mS6CXfO4=
 github.com/lucasb-eyer/go-colorful v1.0.2/go.mod h1:0MS4r+7BZKSJ5mw4/S5MPN+qHFF1fYclkSPilDOKW0s=
@@ -244,9 +251,12 @@ github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnIn
 github.com/spf13/viper v1.0.2/go.mod h1:A8kyI5cUJhb8N+3pkfONlcEcZbueH6nhAm0Fq7SrnBM=
 github.com/spf13/viper v1.3.2 h1:VUFqw5KcqRf7i70GOzW7N+Q7+gxVBkSSqiXB12+JQ4M=
 github.com/spf13/viper v1.3.2/go.mod h1:ZiWeW+zYFKm7srdB9IoDzzZXaJaI5eL9QjNiN/DMA2s=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 github.com/theckman/goconstraint v1.11.0 h1:oBUwN5wpE4dwyPhRGraEgJsFTr+JtLWiDnaJZJeeXI0=
 github.com/theckman/goconstraint v1.11.0/go.mod h1:zkCR/f2kOULTk/h1ujgyB9BlCNLaqlQ6GN2Zl4mg81g=
 github.com/timakin/bodyclose v0.0.0-20190407043127-4a873e97b2bb h1:lI9ufgFfvuqRctP9Ny8lDDLbSWCMxBPletcSqrnyFYM=

logger/logger.go

@@ -20,6 +20,7 @@ type Logger interface {
 	WithField(field string, val interface{}) Logger
 	WithFields(fields Fields) Logger
 	WithError(err error) Logger
+	Log(level Level, msg string)
 	Debug(msg string)
 	Info(msg string)
 	Warn(msg string)
@@ -158,6 +159,10 @@ func (l *loggerImpl) WithError(err error) Logger {
 	return l.WithField(FieldError, val)
 }
 
+func (l *loggerImpl) Log(level Level, msg string) {
+	l.log(level, msg)
+}
+
 func (l *loggerImpl) Debug(msg string) {
 	l.log(Debug, msg)
 }

logger/nulllogger.go

@@ -13,6 +13,7 @@ func (n nullLogger) ReplaceField(field string, val interface{}) Logger { return
 func (n nullLogger) WithField(field string, val interface{}) Logger    { return n }
 func (n nullLogger) WithFields(fields Fields) Logger                   { return n }
 func (n nullLogger) WithError(err error) Logger                        { return n }
+func (nullLogger) Log(level Level, msg string)                         {}
 func (nullLogger) Debug(msg string)                                    {}
 func (nullLogger) Info(msg string)                                     {}
 func (nullLogger) Warn(msg string)                                     {}

util/circlog/circlog.go

@@ -0,0 +1,167 @@
+package circlog
+
+import (
+	"fmt"
+	"math/bits"
+	"sync"
+)
+
+const CIRCULARLOG_INIT_SIZE int = 32 << 10
+
+type CircularLog struct {
+	buf         []byte
+	size        int
+	max         int
+	written     int
+	writeCursor int
+	/*
+		Mutex prevents:
+		concurrent writes:
+			buf, size, written, writeCursor in Write([]byte)
+			buf, writeCursor in Reset()
+		data races vs concurrent Write([]byte) calls:
+			size in Size()
+			size, writeCursor in Len()
+			buf, size, written, writeCursor in Bytes()
+	*/
+	mtx sync.Mutex
+}
+
+func NewCircularLog(max int) (*CircularLog, error) {
+	if max <= 0 {
+		return nil, fmt.Errorf("max must be positive")
+	}
+
+	return &CircularLog{
+		size: CIRCULARLOG_INIT_SIZE,
+		buf:  make([]byte, CIRCULARLOG_INIT_SIZE),
+		max:  max,
+	}, nil
+}
+
+func nextPow2Int(n int) int {
+	if n < 1 {
+		panic("can only round up positive integers")
+	}
+	r := uint(n)
+	// Credit: https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
+	r--
+	// Assume at least a 32 bit integer
+	r |= r >> 1
+	r |= r >> 2
+	r |= r >> 4
+	r |= r >> 8
+	r |= r >> 16
+	if bits.UintSize == 64 {
+		r |= r >> 32
+	}
+	r++
+	// Can't exceed max positive int value
+	if r > ^uint(0)>>1 {
+		panic("rounded to larger than int()")
+	}
+	return int(r)
+}
+
+func (cl *CircularLog) Write(data []byte) (int, error) {
+	cl.mtx.Lock()
+	defer cl.mtx.Unlock()
+	n := len(data)
+
+	// Keep growing the buffer by doubling until
+	// hitting cl.max
+	bufAvail := cl.size - cl.writeCursor
+	// If cl.writeCursor wrapped on the last write,
+	// then the buffer is full, not empty.
+	if cl.writeCursor == 0 && cl.written > 0 {
+		bufAvail = 0
+	}
+	if n > bufAvail && cl.size < cl.max {
+		// Add to size, not writeCursor, so as
+		// to not resize multiple times if this
+		// Write() immediately fills up the buffer
+		newSize := nextPow2Int(cl.size + n)
+		if newSize > cl.max {
+			newSize = cl.max
+		}
+		newBuf := make([]byte, newSize)
+		// Reset write cursor to old size if wrapped
+		if cl.writeCursor == 0 && cl.written > 0 {
+			cl.writeCursor = cl.size
+		}
+		copy(newBuf, cl.buf[:cl.writeCursor])
+		cl.buf = newBuf
+		cl.size = newSize
+	}
+
+	// If data to be written is larger than the max size,
+	// discard all but the last cl.size bytes
+	if n > cl.size {
+		data = data[n-cl.size:]
+		// Overwrite the beginning of data
+		// with a string indicating truncation
+		copy(data, []byte("(...)"))
+	}
+	// First copy data to the end of buf. If that wasn't
+	// all of data, then copy the rest to the beginning
+	// of buf.
+	copied := copy(cl.buf[cl.writeCursor:], data)
+	if copied < n {
+		copied += copy(cl.buf, data[copied:])
+	}
+
+	cl.writeCursor = ((cl.writeCursor + copied) % cl.size)
+	cl.written += copied
+	return copied, nil
+}
+
+func (cl *CircularLog) Size() int {
+	cl.mtx.Lock()
+	defer cl.mtx.Unlock()
+	return cl.size
+}
+
+func (cl *CircularLog) Len() int {
+	cl.mtx.Lock()
+	defer cl.mtx.Unlock()
+	if cl.written >= cl.size {
+		return cl.size
+	} else {
+		return cl.writeCursor
+	}
+}
+
+func (cl *CircularLog) TotalWritten() int {
+	cl.mtx.Lock()
+	defer cl.mtx.Unlock()
+
+	return cl.written
+}
+
+func (cl *CircularLog) Reset() {
+	cl.mtx.Lock()
+	defer cl.mtx.Unlock()
+	cl.writeCursor = 0
+	cl.buf = make([]byte, CIRCULARLOG_INIT_SIZE)
+	cl.size = CIRCULARLOG_INIT_SIZE
+}
+
+func (cl *CircularLog) Bytes() []byte {
+	cl.mtx.Lock()
+	defer cl.mtx.Unlock()
+	switch {
+	case cl.written >= cl.size && cl.writeCursor == 0:
+		return cl.buf
+	case cl.written > cl.size:
+		ret := make([]byte, cl.size)
+		copy(ret, cl.buf[cl.writeCursor:])
+		copy(ret[cl.size-cl.writeCursor:], cl.buf[:cl.writeCursor])
+		return ret
+	default:
+		return cl.buf[:cl.writeCursor]
+	}
+}
+
+func (cl *CircularLog) String() string {
+	return string(cl.Bytes())
+}

util/circlog/circlog_test.go

@@ -0,0 +1,144 @@
+package circlog_test
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/zrepl/zrepl/util/circlog"
+)
+
+func TestCircularLog(t *testing.T) {
+	var maxCircularLogSize int = 1 << 20
+
+	writeFixedSize := func(w io.Writer, size int) (int, error) {
+		pattern := []byte{0xDE, 0xAD, 0xBE, 0xEF}
+		writeBytes := bytes.Repeat(pattern, size/4)
+		if len(writeBytes) < size {
+			writeBytes = append(writeBytes, pattern[:size-len(writeBytes)]...)
+		}
+		n, err := w.Write(writeBytes)
+		if err != nil {
+			return n, err
+		}
+		return n, nil
+	}
+
+	t.Run("negative-size-error", func(t *testing.T) {
+		_, err := circlog.NewCircularLog(-1)
+		require.EqualError(t, err, "max must be positive")
+	})
+
+	t.Run("no-resize", func(t *testing.T) {
+		log, err := circlog.NewCircularLog(maxCircularLogSize)
+		require.NoError(t, err)
+
+		initSize := log.Size()
+		writeSize := circlog.CIRCULARLOG_INIT_SIZE - 1
+		_, err = writeFixedSize(log, writeSize)
+		require.NoError(t, err)
+		finalSize := log.Size()
+		require.Equal(t, initSize, finalSize)
+		require.Equal(t, writeSize, log.Len())
+	})
+	t.Run("one-resize", func(t *testing.T) {
+		log, err := circlog.NewCircularLog(maxCircularLogSize)
+		require.NoError(t, err)
+
+		initSize := log.Size()
+		writeSize := circlog.CIRCULARLOG_INIT_SIZE + 1
+		_, err = writeFixedSize(log, writeSize)
+		require.NoError(t, err)
+		finalSize := log.Size()
+		require.Greater(t, finalSize, initSize)
+		require.LessOrEqual(t, finalSize, maxCircularLogSize)
+		require.Equal(t, writeSize, log.Len())
+	})
+	t.Run("reset", func(t *testing.T) {
+		log, err := circlog.NewCircularLog(maxCircularLogSize)
+		require.NoError(t, err)
+
+		initSize := log.Size()
+		_, err = writeFixedSize(log, maxCircularLogSize)
+		require.NoError(t, err)
+		log.Reset()
+		finalSize := log.Size()
+		require.Equal(t, initSize, finalSize)
+	})
+	t.Run("wrap-exactly-maximum", func(t *testing.T) {
+		log, err := circlog.NewCircularLog(maxCircularLogSize)
+		require.NoError(t, err)
+
+		initSize := log.Size()
+		writeSize := maxCircularLogSize / 4
+		for written := 0; written < maxCircularLogSize; {
+			n, err := writeFixedSize(log, writeSize)
+			written += n
+			require.NoError(t, err)
+		}
+		finalSize := log.Size()
+		require.Greater(t, finalSize, initSize)
+		require.Equal(t, finalSize, maxCircularLogSize)
+		require.Equal(t, finalSize, log.Len())
+	})
+	t.Run("wrap-partial", func(t *testing.T) {
+		log, err := circlog.NewCircularLog(maxCircularLogSize)
+		require.NoError(t, err)
+
+		initSize := log.Size()
+
+		startSentinel := []byte{0x00, 0x00, 0x00, 0x00}
+		_, err = log.Write(startSentinel)
+		require.NoError(t, err)
+
+		nWritesToFill := 4
+		writeSize := maxCircularLogSize / nWritesToFill
+		for i := 0; i < (nWritesToFill + 1); i++ {
+			_, err := writeFixedSize(log, writeSize)
+			require.NoError(t, err)
+		}
+
+		endSentinel := []byte{0xFF, 0xFF, 0xFF, 0xFF}
+		_, err = log.Write(endSentinel)
+		require.NoError(t, err)
+
+		finalSize := log.Size()
+		require.Greater(t, finalSize, initSize)
+		require.Greater(t, log.TotalWritten(), finalSize)
+		require.Equal(t, finalSize, maxCircularLogSize)
+		require.Equal(t, finalSize, log.Len())
+
+		logBytes := log.Bytes()
+
+		require.Equal(t, endSentinel, logBytes[len(logBytes)-len(endSentinel):])
+		require.NotEqual(t, startSentinel, logBytes[:len(startSentinel)])
+	})
+	t.Run("overflow-write", func(t *testing.T) {
+		log, err := circlog.NewCircularLog(maxCircularLogSize)
+		require.NoError(t, err)
+
+		initSize := log.Size()
+		writeSize := maxCircularLogSize + 1
+		n, err := writeFixedSize(log, writeSize)
+		require.NoError(t, err)
+		finalSize := log.Size()
+		require.Less(t, n, writeSize)
+		require.Greater(t, finalSize, initSize)
+		require.Equal(t, finalSize, maxCircularLogSize)
+		logBytes := log.Bytes()
+		require.Equal(t, []byte("(...)"), logBytes[:5])
+	})
+	t.Run("stringify", func(t *testing.T) {
+		log, err := circlog.NewCircularLog(maxCircularLogSize)
+		require.NoError(t, err)
+
+		writtenString := "A harmful truth is better than a useful lie."
+		n, err := log.Write([]byte(writtenString))
+		require.NoError(t, err)
+		require.Equal(t, len(writtenString), n)
+		loggedString := log.String()
+		require.Equal(t, writtenString, loggedString)
+	})
+}

util/circlog/nextpow2int_test.go

@@ -0,0 +1,16 @@
+package circlog
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNextPow2Int(t *testing.T) {
+	require.Equal(t, 512, nextPow2Int(512), "a power of 2 should round to itself")
+	require.Equal(t, 1024, nextPow2Int(513), "should round up to the next power of 2")
+	require.PanicsWithValue(t, "can only round up positive integers", func() { nextPow2Int(0) }, "unimplemented: zero is not positive; corner case")
+	require.PanicsWithValue(t, "can only round up positive integers", func() { nextPow2Int(-1) }, "unimplemented: cannot round up negative numbers")
+	maxInt := int((^uint(0)) >> 1)
+	require.PanicsWithValue(t, "rounded to larger than int()", func() { nextPow2Int(maxInt - 1) }, "cannot round to a number bigger than the int type")
+}