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

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Date:	Sat, 13 Jun 2009 10:20:02 -0400
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ramfs: ignore tmpfs options when we emulate it

On Sat, Jun 13, 2009 at 10:15, 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.

agreed

>> 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
>
> I rather think the correct response to bugzilla #12843 should have
> been to say, either use chmod 1777 yourself, or use CONFIG_SHMEM=y.
> I fear we'll now get a line of requests for support of uid, gid, ...
> in ramfs; whereas ramfs is about blind simplicity, not feature bloat.
> However, that mode= feature is now in, so I guess we ride with it.

i thought the bug report a bit odd in more than just this regard.
glad to see i'm not the only one ;).

>> another option might be to restore the previous behavior where ramfs simply
>> ignored all unknown mount options ...
>
> Yes, that would be my preference, return to the blind simplicity, with
> that one exception for mode=.  Alternative patch suggested at the bottom,
> let's see if Cc's added feel strongly about it one way or another.

i'm OK with either approach, thanks !
-mike
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