On 11/23/2012 02:19 AM, Christoph Hellwig wrote:
> 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?
Yeah, that absolutely makes more sense.
Shaggy
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