Re: [PATCH] Btrfs: prevent deletion of mounted subvolumes

[David Sterba <dsterba@suse.cz>]

On Wed, Apr 01, 2015 at 12:03:28AM -0700, Omar Sandoval wrote:
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -1024,6 +1024,10 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
>  	struct btrfs_root *root = info->tree_root;
>  	char *compress_type;
>  
> +	if (dentry != dentry->d_sb->s_root) {
> +		seq_puts(seq, ",subvol=");
> +		seq_dentry(seq, dentry, " \t\n\\");

Unfortunatelly this does not work if the default subvolume is not the
toplevel one and the implicit mount (ie. without subvol=) is used. Then
this leads to subvol=/ although it should be subvol=/the/default .

There was a patch to build the path in the show_options callback, but it
looked too heavy (taking locks, doing lookups). This is unrelated to the
problem reported by Timo, though the fix might also fix this one.