Btrfs: don't allow the replace procedure on read only filesystems

If you start the replace procedure on a read only filesystem, at
the end the procedure fails to write the updated dev_items to the
chunk tree. The problem is that this error is not indicated except
for a WARN_ON(). If the user now thinks that everything was done
as expected and destroys the source device (with mkfs or with a
hammer). The next mount fails with "failed to read chunk root" and
the filesystem is gone.

This commit adds code to fail the attempt to start the replace
procedure if the filesystem is mounted read-only.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Cc: <stable@vger.kernel.org> # 3.10+
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 076cc7fff813e5ffd23094913ce1fb8ac7a6eb6f..559cb161a60aa303c5f6f3648b409298c6c2c0a9 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3670,6 +3670,9 @@ static long btrfs_ioctl_dev_replace(struct btrfs_root *root, void __user *arg)
 
        switch (p->cmd) {
        case BTRFS_IOCTL_DEV_REPLACE_CMD_START:
+               if (root->fs_info->sb->s_flags & MS_RDONLY)
+                       return -EROFS;
+
                if (atomic_xchg(
                        &root->fs_info->mutually_exclusive_operation_running,
                        1)) {