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

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Date:	Sun, 14 Jun 2009 06:20:11 -0400
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ramfs: ignore tmpfs options when we emulate it

On Sun, Jun 14, 2009 at 06:01, Wu Fengguang wrote:
> 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.
>
> We can avoid the burden of syncing a list of options between
> ramfs<>tmpfs by a slightly differently patch. Hopefully this makes
> ramfs behave like other filesystems when used standalone.

i think Hugh's suggestion to change the behavior of ramfs back to the
way it has always been (ignore unknown options) is the way to go
rather than making it change behavior based on configuration
-mike
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