[PATCH 2/2] btrfs-progs: receive: don't lookup clone root for received subvolume

[Omar Sandoval <osandov@osandov.com>]

From: Omar Sandoval <osandov@fb.com>

When we process a clone request, we look up the source subvolume by
UUID, even if the source is the subvolume that we're currently
receiving. Usually, this is fine. However, if for some reason we
previously received the same subvolume, then this will use paths
relative to the previously received subvolume instead of the current
one. This is incorrect, since the send stream may use temporary names
for the clone source. This can be reproduced as follows:

btrfs subvol create subvol
dd if=/dev/urandom of=subvol/foo bs=1M count=1
cp --reflink subvol/foo subvol/bar
mkdir subvol/dir
mv subvol/foo subvol/dir/
btrfs property set subvol ro true
btrfs send -f stream subvol
mkdir first second
btrfs receive -f stream first
btrfs receive -f stream second

The second receive results in this error:

ERROR: cannot open first/subvol/o259-7-0/foo: No such file or directory

Fix it by always cloning from the current subvolume if its UUID matches.
This has the nice side effect of avoiding unnecessary UUID tree lookups
in that case. Also, while we're here, get rid of some code that has been
commented out since it was added.

Fixes: f1c24cd80dfd ("Btrfs-progs: add btrfs send/receive commands")
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 cmds/receive.c | 34 ++++++++--------------------------
 1 file changed, 8 insertions(+), 26 deletions(-)

diff --git a/cmds/receive.c b/cmds/receive.c
index a3e62985..ed089af2 100644
--- a/cmds/receive.c
+++ b/cmds/receive.c
@@ -753,15 +753,14 @@ static int process_clone(const char *path, u64 offset, u64 len,
 	if (ret < 0)
 		goto out;
 
-	si = subvol_uuid_search(&rctx->sus, 0, clone_uuid, clone_ctransid,
-				NULL,
-				subvol_search_by_received_uuid);
-	if (IS_ERR_OR_NULL(si)) {
-		if (memcmp(clone_uuid, rctx->cur_subvol.received_uuid,
-				BTRFS_UUID_SIZE) == 0) {
-			/* TODO check generation of extent */
-			subvol_path = rctx->cur_subvol_path;
-		} else {
+	if (memcmp(clone_uuid, rctx->cur_subvol.received_uuid,
+		   BTRFS_UUID_SIZE) == 0) {
+		subvol_path = rctx->cur_subvol_path;
+	} else {
+		si = subvol_uuid_search(&rctx->sus, 0, clone_uuid, clone_ctransid,
+					NULL,
+					subvol_search_by_received_uuid);
+		if (IS_ERR_OR_NULL(si)) {
 			if (!si)
 				ret = -ENOENT;
 			else
@@ -769,23 +768,6 @@ static int process_clone(const char *path, u64 offset, u64 len,
 			error("clone: did not find source subvol");
 			goto out;
 		}
-	} else {
-		/*if (rs_args.ctransid > rs_args.rtransid) {
-			if (!r->force) {
-				ret = -EINVAL;
-				fprintf(stderr, "ERROR: subvolume %s was "
-						"modified after it was "
-						"received.\n",
-						r->subvol_parent_name);
-				goto out;
-			} else {
-				fprintf(stderr, "WARNING: subvolume %s was "
-						"modified after it was "
-						"received.\n",
-						r->subvol_parent_name);
-			}
-		}*/
-
 		/* strip the subvolume that we are receiving to from the start of subvol_path */
 		if (rctx->full_root_path) {
 			size_t root_len = strlen(rctx->full_root_path);
-- 
2.22.0