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Re: [PATCH] xfs: Add readpage() check up for mmap file at xfs_file_mmap(

To: Jeff Liu <jeff.liu@xxxxxxxxxx>
Subject: Re: [PATCH] xfs: Add readpage() check up for mmap file at xfs_file_mmap()
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 18 Jul 2012 11:11:48 -0400
Cc: xfs@xxxxxxxxxxx
In-reply-to: <5006CC80.3070208@xxxxxxxxxx>
References: <5006CC80.3070208@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Jul 18, 2012 at 10:47:28PM +0800, Jeff Liu wrote:
> Hello,
> 
> When studying XFS code, I found xfs_file_mmap() does not check whether a 
> specific file has readpage() or not.
> Actually, I have no idea of which kind of file does not supply page reading 
> function, but Btrfs/Ext4
> as well as generic_file_mmap() all do this check at first, do we also need a 
> defense here?

It's not needed. In generic_file_mmap it might make a little sense as
any filesystem could use it, but even there's it's questionable because
->readpage is the only way to actually supposed mmap when using
generic_file_mmap.

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