Re: [PATCH] ramfs: ignore tmpfs options when we emulate it

Wu Fengguang
2009-06-14T12:16:58Z

On Sat, Jun 13, 2009 at 10:15:51PM +0800, Hugh Dickins wrote:
> On Sat, 13 Jun 2009, Mike Frysinger wrote:
>
> > On systems where CONFIG_SHMEM is disabled, mounting tmpfs filesystems can
> > fail when tmpfs options are used. This is because tmpfs creates a small
> > wrapper around ramfs which rejects unknown options, and ramfs itself only
> > supports a tiny subset of what tmpfs supports. This makes it pretty hard
> > to use the same userspace systems across different configuration systems.
> > As such, ramfs should ignore the tmpfs options when tmpfs is merely a
> > wrapper around ramfs.
>
> Yes, indeed, thanks a lot for reporting this.
>
> But I'm uneasy with making ramfs behaviour differ with CONFIG_SHMEM
> (perhaps that's silly: certainly tmpfs behaviour differs with it),
> and uneasy with coding a list of options we need to remember to keep
> in synch with mm/shmem.c. It's easier to justify ignoring all options,
> than rejecting some while ignoring others yet not respecting them.
>
[snip]
> [PATCH] ramfs: ignore unknown mount options
>
> From: Mike Frysinger <vapier@gentoo.org>
>
> On systems where CONFIG_SHMEM is disabled, mounting tmpfs filesystems can
> fail when tmpfs options are used. This is because tmpfs creates a small
> wrapper around ramfs which rejects unknown options, and ramfs itself only
> supports a tiny subset of what tmpfs supports. This makes it pretty hard
> to use the same userspace systems across different configuration systems.
> As such, ramfs should ignore the tmpfs options when tmpfs is merely a
> wrapper around ramfs.
>
> This used to work before commit c3b1b1cbf0 as previously, ramfs would
> ignore all options. But now, we get:
> ramfs: bad mount option: size=10M
> mount: mounting mdev on /dev failed: Invalid argument
>
> Another option might be to restore the previous behavior, where ramfs
> simply ignored all unknown mount options ... which is what Hugh prefers.
>
> Signed-off-by: Mike Frysinger <vapier@gentoo.org>
> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
> Cc: stable@kernel.org
> ---
>
> fs/ramfs/inode.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> --- 2.6.30/fs/ramfs/inode.c 2009-06-10 04:05:27.000000000 +0100
> +++ linux/fs/ramfs/inode.c 2009-06-13 14:45:33.000000000 +0100
> @@ -202,9 +202,12 @@ static int ramfs_parse_options(char *dat
> return -EINVAL;
> opts->mode = option & S_IALLUGO;
> break;
> - default:
> - printk(KERN_ERR "ramfs: bad mount option: %s\n", p);
> - return -EINVAL;
> + /*
> + * We might like to report bad mount options here;
> + * but traditionally ramfs has ignored all mount options,
> + * and as it is used as a !CONFIG_SHMEM simple substitute
> + * for tmpfs, better continue to ignore other mount options.
> + */
> }
> }
>

Acked-by: Wu Fengguang <fengguang.wu@intel.com>