On 2024/11/25 14:01, Christoph Hellwig wrote:
On Mon, Nov 25, 2024 at 05:58:22AM +0000, 韦龙平(Groot) wrote:
What is ZWL? And why mention 6.6? And why do you care about ordering?
ZWL is Zone-Write-Locking and it was replaced by Zone-Write-Plugging on 6.12.
That's not a generally accepted acronym. But more importantly it's all
gone now, so completely irrelevant.
There is no real ordering requirement in the block layer.
According to the design constraints of zoned device, write requests in the same
zone must be dispatched in order of address and there can be no holes in the middle
__bio_split_to_limits will split read bios with max_sectors too, split
read bios in dm-level won't increase the number of requests dispatched
to scsi devices.
Yes. But none of that matters at the device mapper layer. Either the
submitter needs to ensure ordering, or you must use zone append.
Just like what was said in "dm crypt: Fix zoned block device support":
Zone append BIOs (REQ_OP_ZONE_APPEND) always specify the start sector
of the zone to be written instead of the actual sector location to
write. The write location is determined by the device and returned to
the host upon completion of the operation. This interface, while simple
and efficient for writing into sequential zones of a zoned block
device, is incompatible with the use of sector values to calculate a
cypher block IV. All data written in a zone end up using the same IV
values corresponding to the first sectors of the zone, but read
operation will specify any sector within the zone resulting in an IV
mismatch between encryption and decryption.
To solve this problem, report to DM core that zone append operations are
not supported. This result in the zone append operations being emulated
using regular write operations.
Zone append writes to zoned device will be converted to normal write
requests and submitted one by one by zone-write-locking OR
zone-write-plugging.
This patch just want zone-append-emulation which was implemented in
dm-level could works fine even if dm-crypt got a write or zone-append
bio with size greater than max_sectors.
