From 72d288567eb6a76947cc176ff67fcc8771a760e1 Mon Sep 17 00:00:00 2001
From: Christian Schwarz <me@cschwarz.com>
Date: Thu, 5 Oct 2017 19:58:43 +0200
Subject: [PATCH] mappings: fix aliasing bug with '<' wildcards

In contrast to any 'something<' mapping, a '<' mapping cannot be unique
Thus, '<' mappings are thus just an append to target, which is exactly
what we get when trimming empty prefix ''.

Otherwise, given mapping

{ "<": "storage/backups/app-srv" }

Before (clearly a conflict)
zroot     => storage/backups/app-srv
storage   => storage/backups/app-srv
After:
zroot     => storage/backups/app-srv/zroot
storage   => storage/backups/app-srv/storage

However, mapping directly with subtree wildcard is still possible, just
not with the root wildcard

{
    "<"              "storage/backups/app-srv"
    "zroot/var/db<": "storage/db_replication/app-srv"
}

fixes #22
---
 cmd/config_mapfilter.go                         | 9 ++-------
 cmd/config_test.go                              | 4 ++--
 docs/content/configuration/map_filter_syntax.md | 9 ++++-----
 3 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/cmd/config_mapfilter.go b/cmd/config_mapfilter.go
index ac7a24f..c625fc8 100644
--- a/cmd/config_mapfilter.go
+++ b/cmd/config_mapfilter.go
@@ -125,14 +125,9 @@ func (m DatasetMapFilter) Map(source *zfs.DatasetPath) (target *zfs.DatasetPath,
 		return
 	}
 	if me.subtreeMatch {
-		// strip common prefix
+		// strip common prefix ('<' wildcards are no special case here)
 		extendComps := source.Copy()
-		if me.path.Empty() {
-			// special case: trying to map the root => strip first component
-			extendComps.TrimNPrefixComps(1)
-		} else {
-			extendComps.TrimPrefix(me.path)
-		}
+		extendComps.TrimPrefix(me.path)
 		target.Extend(extendComps)
 	}
 	return
diff --git a/cmd/config_test.go b/cmd/config_test.go
index d0d3c91..dbbf439 100644
--- a/cmd/config_test.go
+++ b/cmd/config_test.go
@@ -129,8 +129,8 @@ func TestDatasetMapFilter(t *testing.T) {
 	expectMapping(map1, "a/b/c/d/e", "")
 	expectMapping(map1, "a/b/e", "root2/e")
 	expectMapping(map1, "a/b", "root2")
-	expectMapping(map1, "x", "root3/b/c")
-	expectMapping(map1, "x/y", "root3/b/c/y")
+	expectMapping(map1, "x", "root3/b/c/x")
+	expectMapping(map1, "x/y", "root3/b/c/x/y")
 	expectMapping(map1, "q", "root4/1/2")
 	expectMapping(map1, "b", "")
 	expectMapping(map1, "q/r", "root4/1/2/r")
diff --git a/docs/content/configuration/map_filter_syntax.md b/docs/content/configuration/map_filter_syntax.md
index 6013dda..9eb6aaa 100644
--- a/docs/content/configuration/map_filter_syntax.md
+++ b/docs/content/configuration/map_filter_syntax.md
@@ -45,15 +45,14 @@ tank/var/log     => 1
 
 #### Mappings
 
-Mappings map a *filesystem path* to a *target filesystem*.
+Mappings map a *source filesystem path* to a *target filesystem path*.
 Per pattern, either a target filesystem path or `"!"` is specified as a result.
 
 * If no pattern matches, there exists no target filesystem (`NO MATCH`).
 * If the result is a `"!"`, there exists no target filesystem (`NO MATCH`).
-* If the pattern is a non-wildcard pattern, the filesystem specified on the left is mapped to the target filesystem on the right.
-* If the pattern is a *subtree wildcard* pattern, the root of the subtree specified in the pattern is mapped to the target filesystem on the right and all children are mapped bewlow it.
-
-Note that paths are never appended - a mapping represents a correspondence between a path on the left and a path on the right.
+* If the pattern is a non-wildcard pattern, the source path is mapped to the target path on the right.
+* If the pattern ends with a *subtree wildcard* (`<`), the source path is **prefix-trimmed** with the path specified left of `<`.
+  * Note: this means that only for *wildcard-only* patterns (pattern=`<`) is the source path simply appended to the target path.
 
 The example is from the {{< sampleconflink "localbackup/host1.yml" >}} example config.