linux-kernel - Re: [V2 PATCH] tmpfs: add fallocate support

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Date:	Tue, 22 Nov 2011 13:39:19 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Pekka Enberg <penberg@...nel.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kay Sievers <kay.sievers@...y.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org
Subject: Re: [V2 PATCH] tmpfs: add fallocate support

于 2011年11月21日 05:22, Hugh Dickins 写道:
> On Fri, 18 Nov 2011, Cong Wang wrote:
>
>> It seems that systemd needs tmpfs to support fallocate,
>> see http://lkml.org/lkml/2011/10/20/275. This patch adds
>> fallocate support to tmpfs.
>>
>> As we already have shmem_truncate_range(), it is also easy
>> to add FALLOC_FL_PUNCH_HOLE support too.
>
> Thank you, this version looks much much nicer.
>
> I wouldn't call it bug-free (don't you need a page_cache_release
> after the unlock_page?), and I won't be reviewing it and testing it
> for a week or two - there's a lot about the semantics of fallocate
> and punch-hole that's not obvious, and I'll have to study the mail
> threads discussing them before checking your patch.

Yeah, sorry, I missed unlock_page()...

>
> First question that springs to mind (to which I shall easily find
> an answer): is it actually acceptable for fallocate() to return
> -ENOSPC when it has already completed a part of the work?

Ah, good point, I will fix this as what Christoph suggested.

>
> But so long as the details don't end up complicating this
> significantly, since we anyway want to regularize the punch-hole
> situation by giving tmpfs the same interface to it as other filesystems,
> I now think it would be a bit perverse to disallow the original
> fallocate functionality that you implement here in-kernel.
>

Ok, I think you mean you are fine to accept it now?

Anyway, thanks a lot for your comments!
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