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

[Christoph Hellwig]

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.