[PATCH] xfs: don't perform discard if the given range length is less than block size

[Ben Myers]

On Wed, Nov 20, 2013 at 04:08:53PM +0800, Jeff Liu wrote:
> From: Jie Liu <jeff.liu at oracle.com>
> 
> For discard operation, we should return EINVAL if the given range length
> is less than a block size, otherwise it will go through the file system
> to discard data blocks as the end range might be evaluated to -1, e.g,
> # fstrim -v -o 0 -l 100 /xfs7
> /xfs7: 9811378176 bytes were trimmed
> 
> This issue can be triggered via xfstests/generic/288.
> 
> Also, it seems to get the request queue pointer via bdev_get_queue()
> instead of the hard code pointer dereference is not a bad thing.
> 
> Signed-off-by: Jie Liu <jeff.liu at oracle.com>

Applied this.