btrfs/010: don't run without /sys/fs/btrfs

Older kernels don't have /sys/fs/btrfs.  btrfs/010 will happily run
until it goes to check its work against sysfs and finds those files
don't exist.  This patch introduces a require check to ensure that
the sysfs files are present before running.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

common/btrfs

@@ -89,6 +89,14 @@ _require_btrfs_fs_feature()
 		_notrun "Feature $feat not supported by the available btrfs version"
 }
 
+_require_btrfs_fs_sysfs()
+{
+	modprobe btrfs > /dev/null 2>&1
+	[ -e /sys/fs/btrfs/features ] || \
+		_notrun "Sysfs not supported by the available btrfs version"
+
+}
+
 _check_btrfs_filesystem()
 {
 	device=$1

tests/btrfs/010

@@ -33,6 +33,7 @@ rm -f $seqres.full
 _supported_fs btrfs
 _supported_os Linux
 _require_test
+_require_btrfs_fs_sysfs
 
 # Create 32k extents. All of these extents will be accounted as outstanding and
 # reserved.