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

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Date:	Wed, 23 Nov 2011 12:30:43 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kay Sievers <kay.sievers@...y.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org
Subject: Re: [V2 PATCH] tmpfs: add fallocate support

于 2011年11月23日 06:06, Andrew Morton 写道:
> On Fri, 18 Nov 2011 18:39:50 +0800
> Cong Wang<amwang@...hat.com>  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.
>>
>>
>> ...
>>
>> +static long shmem_fallocate(struct file *file, int mode,
>> +				loff_t offset, loff_t len)
>> +{
>> +	struct inode *inode = file->f_path.dentry->d_inode;
>> +	pgoff_t start = offset>>  PAGE_CACHE_SHIFT;
>> +	pgoff_t end = DIV_ROUND_UP((offset + len), PAGE_CACHE_SIZE);
>> +	pgoff_t index = start;
>> +	loff_t i_size = i_size_read(inode);
>> +	struct page *page = NULL;
>> +	int ret = 0;
>> +
>> +	mutex_lock(&inode->i_mutex);
>
> It would be saner and less racy-looking to read i_size _after_ taking
> i_mutex.
>
> And if you do that, there's no need to use i_size_read() - just a plain
> old
>
> 	i_size = inode->i_size;
>
> is OK.

Fair enough, I will fix that in V3.

Thanks, Andrew!
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