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nspawn: add fallback top normal copy/reflink when we cannot btrfs snapshot

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Given that other file systems (notably: xfs) support reflinks these days, let's
extend the file system snapshotting logic to fall back to plan copies or
reflinks when full btrfs subvolume snapshots are not available.

This essentially makes "systemd-nspawn --ephemeral" and "systemd-nspawn
--template=" available on non-btrfs subvolumes. Of course, both operations will
still be slower on non-btrfs than on btrfs (simply because reflinking each file
individually in a directory tree is still slower than doing this in one step
for a whole subvolume), but it's probably good enough for many cases, and we
should provide the users with the tools, they have to figure out what's good
for them.

Note that "machinectl clone" already had a fallback like this in place, this
patch generalizes this, and adds similar support to our other cases.
This commit is contained in:
Lennart Poettering
2016-11-22 13:35:09 +01:00
parent c67b008273
commit 17cbb288fa
7 changed files with 80 additions and 58 deletions
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src/shared/machine-image.c
+8 -8
View File
@@ -609,14 +609,14 @@ int image_clone(Image *i, const char *new_name, bool read_only) {
new_path = strjoina("/var/lib/machines/", new_name);
r = btrfs_subvol_snapshot(i->path, new_path, (read_only ? BTRFS_SNAPSHOT_READ_ONLY : 0) | BTRFS_SNAPSHOT_FALLBACK_COPY | BTRFS_SNAPSHOT_RECURSIVE | BTRFS_SNAPSHOT_QUOTA);
if (r == -EOPNOTSUPP) {
/* No btrfs snapshots supported, create a normal directory then. */
r = copy_directory(i->path, new_path, false);
if (r >= 0)
(void) chattr_path(new_path, read_only ? FS_IMMUTABLE_FL : 0, FS_IMMUTABLE_FL);
} else if (r >= 0)
r = btrfs_subvol_snapshot(i->path, new_path,
(read_only ? BTRFS_SNAPSHOT_READ_ONLY : 0) |
BTRFS_SNAPSHOT_FALLBACK_COPY |
BTRFS_SNAPSHOT_FALLBACK_DIRECTORY |
BTRFS_SNAPSHOT_FALLBACK_IMMUTABLE |
BTRFS_SNAPSHOT_RECURSIVE |
BTRFS_SNAPSHOT_QUOTA);
if (r >= 0)
/* Enable "subtree" quotas for the copy, if we didn't copy any quota from the source. */
(void) btrfs_subvol_auto_qgroup(new_path, 0, true);