On Wed, Nov 21, 2012 at 04:40:49PM -0600, Dave Kleikamp wrote:
> From: Zach Brown <zab@xxxxxxxxx>
>
> __blockdev_direct_IO() had two instances of the same code to determine
> if a given offset wasn't aligned first to the inode's blkbits and then
> to the underlying device's blkbits. This was confusing enough but
> we're about to add code that performs the same check on offsets in bvec
> arrays. Rather than add yet more copies of this code let's have
> everyone call a helper.
>
> Signed-off-by: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
> Cc: Zach Brown <zab@xxxxxxxxx>
> ---
> fs/direct-io.c | 59 ++++++++++++++++++++++++++++++++++++----------------------
> 1 file changed, 37 insertions(+), 22 deletions(-)
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index f86c720..035c0a3 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -1020,6 +1020,39 @@ static inline int drop_refcount(struct dio *dio)
> }
>
> /*
> + * Returns true if the given offset is aligned to either the IO size
> + * specified by the given blkbits or by the logical block size of the
> + * given block device.
> + *
> + * If the given offset isn't aligned to the blkbits arguments as this is
> + * called then blkbits is set to the block size of the specified block
> + * device. The call can then return either true or false.
> + *
> + * This bizarre calling convention matches the code paths that
> + * duplicated the functionality that this helper was built from. We
> + * reproduce the behaviour to avoid introducing subtle bugs.
> + */
> +static int dio_aligned(unsigned long offset, unsigned *blkbits,
> + struct block_device *bdev)
> +{
> + unsigned mask = (1 << *blkbits) - 1;
> +
> + /*
> + * Avoid references to bdev if not absolutely needed to give
> + * the early prefetch in the caller enough time.
> + */
> +
> + if (offset & mask) {
> + if (bdev)
> + *blkbits = blksize_bits(bdev_logical_block_size(bdev));
I don't like having the blkbits assignment hidden in the helper,
shouldn't we have a:
if (bdev)
blkbits = blksize_bits(bdev_logical_block_size(bdev));
else
blkbits = inode->i_blkbits;
in the caller instead?
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