linux-kernel - Re: [PATCH -mm] splice: Disable vmsplice on nommu.

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Message-ID: <20070911093510.GA15405@kernel.dk>
Date:	Tue, 11 Sep 2007 11:35:11 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Paul Mundt <lethal@...ux-sh.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	Greg Ungerer <gerg@...pgear.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] splice: Disable vmsplice on nommu.

On Tue, Sep 11 2007, Paul Mundt wrote:
> The vmsplice rework in -mm breaks nommu:
> 
> fs/built-in.o: In function `splice_setup_vma':
> fs/splice.c:1272: undefined reference to `may_expand_vm'
> fs/splice.c:1272: undefined reference to `protection_map'
> fs/splice.c:1272: undefined reference to `insert_vm_struct'
> fs/splice.c:1272: undefined reference to `vm_stat_account'
> 
> This is going to be non-trivial to wire up properly on nommu, and
> it's debateable whether there's even any point in trying. For now,
> disable vmsplice if CONFIG_MMU=n and wire it up as a cond syscall
> for the platforms that support both.

It's a bit of a sledge hammer... Since get_user_pages() appears to work
on nummu, we can just disable the vmsplice-to-userspace bits and leave
the (working) vmsplice-from-userspace in place.

I'm reworking this code anyway in the block branches, so I'll update and
take CONFIG_MMU into consideration.

-- 
Jens Axboe

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