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Merge pull request #99 from Misterio77/allow-symlinking-directories
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home-manager: adds configurable symlink/bindfs option
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@talyz
talyz authored Aug 27, 2022
2 parents e7c6fbb + fc9ca99 commit 2237ad2
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15 changes: 11 additions & 4 deletions README.org
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Original file line number Diff line number Diff line change
Expand Up @@ -199,6 +199,10 @@
".nixops"
".local/share/keyrings"
".local/share/direnv"
{
directory = ".local/share/Steam";
method = "symlink";
}
];
files = [
".screenrc"
Expand All @@ -210,7 +214,10 @@

- ~"/persistent/home/talyz"~ is the path to your persistent storage location
- ~directories~ are all directories you want to link to persistent storage
- ~files~ are all files you want to link to persistent storage
- It is possible to switch the linking ~method~ between bindfs (the
default) and symbolic links.
- ~files~ are all files you want to link to persistent storage. These are
symbolic links to their target location.
- ~allowOther~ allows other users, such as ~root~, to access files
through the bind mounted directories listed in
~directories~. Useful for ~sudo~ operations, Docker, etc. Requires
Expand Down Expand Up @@ -240,9 +247,9 @@
removes the first part of the path when deciding where to put the
links.

/Note:/ Since this module uses the ~bindfs~ fuse filesystem for
directories, the names of the directories you add will be visible
in the ~/etc/mtab~ file and in the output of ~mount~ to all users.
/Note:/ When using ~bindfs~ fuse filesystem for directories, the names of
the directories you add will be visible in the ~/etc/mtab~ file and in the
output of ~mount~ to all users.

** Further reading
The following blog posts provide more information on the concept of ephemeral
Expand Down
143 changes: 102 additions & 41 deletions home-manager.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,32 @@ let

persistentStoragePaths = attrNames cfg;

getDirPath = v: if isString v then v else v.directory;
getDirMethod = v: v.method or "bindfs";
isBindfs = v: (getDirMethod v) == "bindfs";
isSymlink = v: (getDirMethod v) == "symlink";

inherit (pkgs.callPackage ./lib.nix { }) splitPath dirListToPath concatPaths sanitizeName;

mount = "${pkgs.util-linux}/bin/mount";
unmountScript = mountPoint: tries: sleep: ''
triesLeft=${toString tries}
if ${mount} | grep -F ${mountPoint}' ' >/dev/null; then
while (( triesLeft > 0 )); do
if fusermount -u ${mountPoint}; then
break
else
(( triesLeft-- ))
if (( triesLeft == 0 )); then
echo "Couldn't perform regular unmount of ${mountPoint}. Attempting lazy unmount."
fusermount -uz ${mountPoint}
else
sleep ${toString sleep}
fi
fi
done
fi
'';
in
{
options = {
Expand All @@ -18,7 +43,25 @@ in
options =
{
directories = mkOption {
type = with types; listOf str;
type = with types; listOf (either str (submodule {
options = {
directory = mkOption {
type = str;
default = null;
description = "The directory path to be linked.";
};
method = mkOption {
type = types.enum [ "bindfs" "symlink" ];
default = "bindfs";
description = ''
The linking method that should be used for this
directory. bindfs is the default and works for most use
cases, however some programs may behave better with
symlinks.
'';
};
};
}));
default = [ ];
example = [
"Downloads"
Expand All @@ -31,10 +74,15 @@ in
".ssh"
".local/share/keyrings"
".local/share/direnv"
{
directory = ".local/share/Steam";
method = "symlink";
}
];
description = ''
A list of directories in your home directory that
you want to link to persistent storage.
you want to link to persistent storage. You may optionally
specify the linking method each directory should use.
'';
};

Expand Down Expand Up @@ -119,6 +167,10 @@ in
".nixops"
".local/share/keyrings"
".local/share/direnv"
{
directory = ".local/share/Steam";
method = "symlink";
}
];
files = [
".screenrc"
Expand All @@ -140,19 +192,20 @@ in
{ }
"ln -s '${file}' $out";

mkLinkNameValuePair = persistentStoragePath: file: {
mkLinkNameValuePair = persistentStoragePath: fileOrDir: {
name =
if cfg.${persistentStoragePath}.removePrefixDirectory then
dirListToPath (tail (splitPath [ file ]))
dirListToPath (tail (splitPath [ fileOrDir ]))
else
file;
value = { source = link (concatPaths [ persistentStoragePath file ]); };
fileOrDir;
value = { source = link (concatPaths [ persistentStoragePath fileOrDir ]); };
};

mkLinksToPersistentStorage = persistentStoragePath:
listToAttrs (map
(mkLinkNameValuePair persistentStoragePath)
(cfg.${persistentStoragePath}.files)
(map getDirPath (cfg.${persistentStoragePath}.files ++
(filter isSymlink cfg.${persistentStoragePath}.directories)))
);
in
foldl' recursiveUpdate { } (map mkLinksToPersistentStorage persistentStoragePaths);
Expand Down Expand Up @@ -187,20 +240,7 @@ in
'';
stopScript = pkgs.writeShellScript "unmount-${name}" ''
set -eu
triesLeft=6
while (( triesLeft > 0 )); do
if fusermount -u ${mountPoint}; then
exit 0
else
(( triesLeft-- ))
if (( triesLeft == 0 )); then
echo "Couldn't perform regular unmount of ${mountPoint}. Attempting lazy unmount."
fusermount -uz ${mountPoint}
else
sleep 5
fi
fi
done
${unmountScript mountPoint 6 5}
'';
in
{
Expand Down Expand Up @@ -240,7 +280,7 @@ in
mkBindMountServicesForPath = persistentStoragePath:
listToAttrs (map
(mkBindMountService persistentStoragePath)
cfg.${persistentStoragePath}.directories
(map getDirPath (filter isBindfs cfg.${persistentStoragePath}.directories))
);
in
builtins.foldl'
Expand All @@ -251,6 +291,7 @@ in
home.activation =
let
dag = config.lib.dag;
mount = "${pkgs.util-linux}/bin/mount";

# The name of the activation script entry responsible for
# reloading systemd user services. The name was initially
Expand All @@ -270,7 +311,6 @@ in
dir;
targetDir = escapeShellArg (concatPaths [ persistentStoragePath dir ]);
mountPoint = escapeShellArg (concatPaths [ config.home.homeDirectory mountDir ]);
mount = "${pkgs.util-linux}/bin/mount";
bindfsOptions = concatStringsSep "," (
optional (!cfg.${persistentStoragePath}.allowOther) "no-allow-other"
++ optional (versionAtLeast pkgs.bindfs.version "1.14.9") "fsname=${targetDir}"
Expand Down Expand Up @@ -304,7 +344,7 @@ in
mkBindMountsForPath = persistentStoragePath:
concatMapStrings
(mkBindMount persistentStoragePath)
cfg.${persistentStoragePath}.directories;
(map getDirPath (filter isBindfs cfg.${persistentStoragePath}.directories));

mkUnmount = persistentStoragePath: dir:
let
Expand All @@ -317,31 +357,52 @@ in
in
''
if [[ -n ''${mountedPaths[${mountPoint}]+x} ]]; then
triesLeft=3
while (( triesLeft > 0 )); do
if fusermount -u ${mountPoint}; then
break
else
(( triesLeft-- ))
if (( triesLeft == 0 )); then
echo "Couldn't perform regular unmount of ${mountPoint}. Attempting lazy unmount."
fusermount -uz ${mountPoint} || true
else
sleep 1
fi
fi
done
${unmountScript mountPoint 3 1}
fi
'';

mkUnmountsForPath = persistentStoragePath:
concatMapStrings
(mkUnmount persistentStoragePath)
cfg.${persistentStoragePath}.directories;
(map getDirPath (filter isBindfs cfg.${persistentStoragePath}.directories));

mkLinkCleanup = persistentStoragePath: dir:
let
mountDir =
if cfg.${persistentStoragePath}.removePrefixDirectory then
dirListToPath (tail (splitPath [ dir ]))
else
dir;
mountPoint = escapeShellArg (concatPaths [ config.home.homeDirectory mountDir ]);
in
''
# Unmount if it's mounted. Ensures smooth transition: bindfs -> symlink
${unmountScript mountPoint 3 1}
# If it is a directory and it's empty
if [ -d ${mountPoint} ] && [ -z "$(ls -A ${mountPoint})" ]; then
echo "Removing empty directory ${mountPoint}"
rm -d ${mountPoint}
fi
'';

mkLinkCleanupForPath = persistentStoragePath:
concatMapStrings
(mkLinkCleanup persistentStoragePath)
(map getDirPath (filter isSymlink cfg.${persistentStoragePath}.directories));


in
mkMerge [
(mkIf (any (path: cfg.${path}.directories != [ ]) persistentStoragePaths) {
# Clean up existing empty directories in the way of links
cleanEmptyLinkTargets =
dag.entryBefore
[ "checkLinkTargets" ]
''
${concatMapStrings mkLinkCleanupForPath persistentStoragePaths}
'';

createAndMountPersistentStoragePaths =
dag.entryBefore
[ "writeBoundary" ]
Expand Down Expand Up @@ -370,7 +431,7 @@ in
unmountBindMounts
'';
})
(mkIf (any (path: cfg.${path}.files != [ ]) persistentStoragePaths) {
(mkIf (any (path: (cfg.${path}.files != [ ]) || ((filter isSymlink cfg.${path}.directories) != [ ])) persistentStoragePaths) {
createTargetFileDirectories =
dag.entryBefore
[ "writeBoundary" ]
Expand All @@ -380,7 +441,7 @@ in
(targetFilePath: ''
mkdir -p ${escapeShellArg (concatPaths [ persistentStoragePath (dirOf targetFilePath) ])}
'')
cfg.${persistentStoragePath}.files)
(map getDirPath (cfg.${persistentStoragePath}.files ++ (filter isSymlink cfg.${persistentStoragePath}.directories))))
persistentStoragePaths);
})
];
Expand Down

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