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

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Date:	Sun, 14 Jun 2009 18:43:25 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Mike Frysinger <vapier.adi@...il.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 06:20:11PM +0800, Mike Frysinger wrote:
> 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

Right. I've just posted a new patch. Does that make sense to you?

Thanks,
Fengguang
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