On 12/15/2015 04:49 PM, Christoph Hellwig wrote:
Hi Bart,
I think this is moving in the wrong directions for two different
reasons:
- first we do not split or align bios at the top of the stack since
Linux 4.3. Any fine tuning should be fon in blk_bio_discard_split
instead.
- second a discard does not guarantee data is zeroed, so there is no
need to a manual zeroing of unaligned regions for a plain discard.
Hello Christoph,
Maybe I should explain why I started looking into this. If LIO exports a
block device for which the discard_zeroes_data flag has been set then it
would be possible for LIO to set the LBPRZ bit in the READ CAPACITY(16)
response (something it does not yet do today). If the granularity of
discard requests of the block device is larger than the block size of
the SCSI device, which layer should then handle the start and end blocks
of the SCSI UNMAP command if the start and/or end are not aligned on a
discard boundary ? Should the caller of blkdev_issue_discard() implement
this or should this functionality be added in blkdev_issue_discard()
itself ?
Thanks,
Bart.
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