[PATCH v2] btrfs: fix _require_btrfs_send_version to detect btrfs-progs support

[fdmanana@kernel.org]

From: Filipe Manana <fdmanana@suse.com>

Commit 199d0a992536df3702a0c4843d2a449d54f399c2 ("common/btrfs: introduce
_require_btrfs_send_version") turned _require_btrfs_send_v2 into a generic
helper to detect support for any send stream version, however it's only
working for detecting kernel support, it misses detecting the support from
btrfs-progs - it always checks only that it supports v2 (the send command
supports the --compressed-data option).

Fix that by verifying that btrfs-progs supports the requested version.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---

V2: Don't use -f /dev/null in the send command, just redirect stdout and
    stderr to /dev/null.
    Add Qu's review tag.

 common/btrfs | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/common/btrfs b/common/btrfs
index be5948db..c0be7c08 100644
--- a/common/btrfs
+++ b/common/btrfs
@@ -777,17 +777,29 @@ _require_btrfs_corrupt_block()
 _require_btrfs_send_version()
 {
 	local version=$1
+	local ret
 
-	# Check first if btrfs-progs supports the v2 stream.
-	_require_btrfs_command send --compressed-data
-
-	# Now check the kernel support. If send_stream_version does not exists,
+	# Check the kernel support. If send_stream_version does not exists,
 	# then it's a kernel that only supports v1.
 	[ -f /sys/fs/btrfs/features/send_stream_version ] || \
 		_notrun "kernel does not support send stream $version"
 
 	[ $(cat /sys/fs/btrfs/features/send_stream_version) -ge $version ] || \
 		_notrun "kernel does not support send stream $version"
+
+	# Now check that btrfs-progs supports the requested stream version.
+	_scratch_mkfs &> /dev/null || \
+		_fail "mkfs failed at _require_btrfs_send_version"
+	_scratch_mount
+	$BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT \
+			 $SCRATCH_MNT/snap &> /dev/null
+	$BTRFS_UTIL_PROG send --proto $version $SCRATCH_MNT/snap &> /dev/null
+	ret=$?
+	_scratch_unmount
+
+	if [ $ret -ne 0 ]; then
+		_notrun "btrfs-progs does not support send stream version $version"
+	fi
 }
 
 # Get the bytenr associated to a file extent item at a given file offset.
-- 
2.43.0