have new mount points be owned by their parent's owner

lib/setup-scripts/disk.sh

@@ -215,7 +215,6 @@ function fix-grub-install {
     fi
 }
 
-
 ## Mounts all file systems as it would happen during boot, but at path prefix »$mnt« (instead of »/«).
 function mount-system {( # 1: mnt, 2?: fstabPath, 3?: allowFail
     # While not generally required for fstab, nixos uses the dependency-sorted »config.system.build.fileSystems« list (instead of plain »builtins.attrValues config.fileSystems«) to generate »/etc/fstab« (provided »config.fileSystems.*.depends« is set correctly, e.g. for overlay mounts).
@@ -230,19 +229,19 @@ function mount-system {( # 1: mnt, 2?: fstabPath, 3?: allowFail
         options=,$options, ; options=${options//,ro,/,}
 
         if ! @{native.util-linux}/bin/mountpoint -q "$mnt"/"$target" ; then (
-            mkdir -p "$mnt"/"$target" || exit
+            mkdir-sticky "$mnt"/"$target" || exit
             [[ $type == tmpfs || $type == auto || $type == */* ]] || @{native.kmod}/bin/modprobe --quiet $type || true # (this does help sometimes)
 
             if [[ $type == overlay ]] ; then
                 options=${options//,workdir=/,workdir=$mnt\/} ; options=${options//,upperdir=/,upperdir=$mnt\/} # Work and upper dirs must be in target.
-                workdir=$(  <<<"$options" grep -o -P ',workdir=\K[^,]+'  || true ) ; if [[ $workdir  ]] ; then mkdir -p "$workdir"  ; fi
+                workdir=$(  <<<"$options" grep -o -P ',workdir=\K[^,]+'  || true ) ; if [[ $workdir  ]] ; then mkdir-sticky "$workdir"  ; fi
-                upperdir=$( <<<"$options" grep -o -P ',upperdir=\K[^,]+' || true ) ; if [[ $upperdir ]] ; then mkdir -p "$upperdir" ; fi
+                upperdir=$( <<<"$options" grep -o -P ',upperdir=\K[^,]+' || true ) ; if [[ $upperdir ]] ; then mkdir-sticky "$upperdir" ; fi
                 lowerdir=$( <<<"$options" grep -o -P ',lowerdir=\K[^,]+' || true )
                 options=${options//,lowerdir=$lowerdir,/,lowerdir=$mnt/${lowerdir//:/:$mnt\/},} ; source=overlay
                 # TODO: test the lowerdir stuff
             elif [[ $options =~ ,r?bind, ]] ; then
                 if [[ $source == /nix/store/* ]] ; then options=,ro$options ; fi
-                source=$mnt/$source ; if [[ ! -e $source ]] ; then mkdir -p "$source" || exit ; fi
+                source=$mnt/$source ; if [[ ! -e $source ]] ; then mkdir-sticky "$source" || exit ; fi
             fi
 
             @{native.util-linux}/bin/mount -t $type -o "${options:1:(-1)}" "$source" "$mnt"/"$target" || exit

lib/setup-scripts/utils.sh

@@ -74,6 +74,24 @@ function copy-function { # 1: existingName, 2: newName
     eval "${original/$1/${2?newName not provided}}" # run the code declaring the function again, replacing only the first occurrence of the name
 }
 
+## Ensures that a directory exists, like »mkdir -p«, but for any new path elements created, copies the user/group/mode of the closest existing parent.
+#  Only uses the fallback user/group/mode when the closest existing parent is already a sticky dir (whose (root-)ownership does not mean much, as it is meant for children owned by any/other user(s), like /tmp).
+function mkdir-sticky { # 1: path, 2?: fallbackOwner, 3?: fallbackGroup, 4?: fallbackMode
+    local path ; path=$1 ; shift
+    if [[ -d $path ]] ; then return ; fi # existing (symlink to existing) dir
+    if [[ -L $path || -e $path ]] ; then echo "Can't create (child of) existing file (or broken symlink) '$path'" 1>&2 ; return 1 ; fi
+    local parent ; parent=$( dirname "$path" ) || return
+    mkdir-sticky "$parent" "$@" || return
+    parent=$( realpath "$parent" ) || return
+    stat=( $( stat --format '%u %g %a' "$parent" ) ) || return
+    if [[ ${stat[2]} =~ ^1...$ ]] ; then # sticky parent
+        #echo "Can't infer correct ownership/permissions for child '$( basename "$path" )' of sticky dir '$parent'" 1>&2 ; return 1
+        install --directory --owner="${1:-0}" --group="${2:-0}" ${3+--mode="$3"} "$path" || return
+    else
+        install --directory --owner=${stat[0]} --group=${stat[1]} --mode=${stat[2]} "$path" || return
+    fi
+}
+
 ## Writes a »$name«d secret from stdin to »$targetDir«, ensuring proper file permissions.
 function write-secret {( set -u # 1: path, 2?: owner[:[group]], 3?: mode
     mkdir -p -- "$(dirname "$1")"/ || exit
@@ -136,7 +154,7 @@ function build-lazy { # 1: drvPath, 2?: output
 }
 
 ## Tests whether (returns 0/success if) the first version argument is greater/less than (or equal) the second version argument.
-function version-gr-eq { printf '%s\n%s' "$1" "$2" | sort -C -V -r; }
+function version-gr-eq { printf '%s\n%s' "$1" "$2" | sort -C -V -r ; }
 function version-lt-eq { printf '%s\n%s' "$1" "$2" | sort -C -V ; }
 function version-gt { ! version-gt-eq "$2" "$1" ; }
 function version-lt { ! version-lt-eq "$2" "$1" ; }