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

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.

1 files changed, 6 insertions, 6 deletions

diff --git a/src/import/pull-common.c b/src/import/pull-common.c
index 2ae2a4174c..5ddc0c56f4 100644
--- a/src/import/pull-common.c
+++ b/src/import/pull-common.c
@@ -144,12 +144,12 @@ int pull_make_local_copy(const char *final, const char *image_root, const char *
         if (force_local)
                 (void) rm_rf(p, REMOVE_ROOT|REMOVE_PHYSICAL|REMOVE_SUBVOLUME);
 
-        r = btrfs_subvol_snapshot(final, p, BTRFS_SNAPSHOT_QUOTA);
-        if (r == -ENOTTY) {
-                r = copy_tree(final, p, false);
-                if (r < 0)
-                        return log_error_errno(r, "Failed to copy image: %m");
-        } else if (r < 0)
+        r = btrfs_subvol_snapshot(final, p,
+                                  BTRFS_SNAPSHOT_QUOTA|
+                                  BTRFS_SNAPSHOT_FALLBACK_COPY|
+                                  BTRFS_SNAPSHOT_FALLBACK_DIRECTORY|
+                                  BTRFS_SNAPSHOT_RECURSIVE);
+        if (r < 0)
                 return log_error_errno(r, "Failed to create local image: %m");
 
         log_info("Created new local image '%s'.", local);