Re: [patch 4/6] vfs: mountinfo show dominating group id

[Al Viro <viro@ZenIV.linux.org.uk>]

On Thu, Mar 13, 2008 at 10:26:45PM +0100, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Show peer group ID of nearest dominating group that has intersection
> with the mount's namespace.

There's an obvious problem here: ->show_options() can spew _anything_,
including a string that ends on " shared:42".  Makes reliable parsing of
the damn thing in userland impossible.  IOW, fs options should go _last_
and they should follow an unconditionally present field.

>  	if (sb->s_op->show_options)
>  		err = sb->s_op->show_options(m, mnt);
> -	if (IS_MNT_SHARED(mnt)) {
> -		seq_printf(m, " shared:%i", get_peer_group_id(mnt));
> -		if (IS_MNT_SLAVE(mnt))
> -			seq_printf(m, ",slave:%i", get_master_id(mnt));
> -	} else if (IS_MNT_SLAVE(mnt)) {
> -		seq_printf(m, " slave:%i", get_master_id(mnt));
> +	seq_putc(m, ' ');
> +	if (IS_MNT_SHARED(mnt) || IS_MNT_SLAVE(mnt)) {
> +		if (IS_MNT_SHARED(mnt))
> +			seq_printf(m, "shared:%i", get_peer_group_id(mnt));
> +		if (IS_MNT_SLAVE(mnt)) {
> +			int dominator_id = get_dominator_id_same_ns(mnt);