linux-kernel - Re: [Patch] tmpfs: add fallocate support

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Date:	Wed, 16 Nov 2011 15:21:55 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Cong Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	Lennart Poettering <lennart@...ttering.net>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [Patch] tmpfs: add fallocate support

On Wed, 2011-11-16 at 15:21 +0800, Cong Wang wrote:
> 于 2011年11月16日 01:43, Dave Hansen 写道:
> > On Tue, 2011-11-15 at 18:23 +0800, Cong Wang wrote:
> >>> +	if (!(mode&   FALLOC_FL_KEEP_SIZE)) {
> >>> +		ret = inode_newsize_ok(inode, (offset + len));
> >>> +		if (ret)
> >>> +			return ret;
> >>> +	}
> >
> > inode_newsize_ok()'s comments say:
> >
> >   * inode_newsize_ok must be called with i_mutex held.
> >
> > But I don't see any trace of it.
> 
> Hmm, even for tmpfs? I see none of the tmpfs code takes
> i_mutex lock though...

Look harder. :)

ramfs/tmpfs for a large part just used the generic VFS functions to do
their work since they're page-cache based.  For instance:

static const struct file_operations shmem_file_operations = {
...
        .aio_write      = generic_file_aio_write,

IOW, you need to check beyond mm/shmem.c.

-- Dave

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