btrfs-progs: receive: better error reporting for snapshots

Two fixes:

1)

Check that the parent subvol actually is reachable via our root path.
The previous code wouldn't catch

    parent subvol: foo/bar
    root path:     bar   (i.e. mounted with -o subvol=bar)

where the parent isn't reachable from the root path.
(but the original "strstr(parent, root_path) == NULL" check still doesn't hold)

Also check for the slash after "root_path", i.e. throw an error on

    parent subvol: foobar
    root path:     foo

2)

If the parent subvol is the one that is mounted we obviously can't
receive into it, as it has to be read-only by definition.

We'd get a rather cryptic:

    At subvol /tmp/test/dest.snap
    At snapshot dest.snap
    ERROR: creating snapshot / -> dest.snap failed: Invalid cross-device link

(not sure what it says if "/" isn't even a btrfs)

But with this we get

    At subvol /tmp/test/dest.snap
    At snapshot dest.snap
    ERROR: creating snapshot . -> dest.snap failed: Read-only file system

which is both more helpful and more correct.

Signed-off-by: Benedikt Morbach <benedikt.morbach@googlemail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/cmds-receive.c b/cmds-receive.c
index df86c03..06e6177 100644 (file)
--- a/cmds-receive.c
+++ b/cmds-receive.c
@@ -315,8 +315,8 @@ static int process_snapshot(const char *path, const u8 *uuid, u64 ctransid,
                sub_len = strlen(parent_subvol->path);
 
                /* First make sure the parent subvol is actually in our path */
-               if (sub_len < root_len ||
-                   strstr(parent_subvol->path, rctx->full_root_path) == NULL) {
+               if (strstr(parent_subvol->path, rctx->full_root_path) != parent_subvol->path ||
+                   (sub_len > root_len && parent_subvol->path[root_len] != '/')) {
                        error(
                "parent subvol is not reachable from inside the root subvol");
                        ret = -ENOENT;
@@ -324,7 +324,7 @@ static int process_snapshot(const char *path, const u8 *uuid, u64 ctransid,
                }
 
                if (sub_len == root_len) {
-                       parent_subvol->path[0] = '/';
+                       parent_subvol->path[0] = '.';
                        parent_subvol->path[1] = '\0';
                } else {
                        /*