Re: [Qemu-devel] [PATCH v3 00/29] block: Support for 512b-on-4k emulation

[Christian Borntraeger]

On 17/01/14 15:14, Kevin Wolf wrote:
> This patch series adds code to the block layer that allows performing
> I/O requests in smaller granularities than required by the host backend
> (most importantly, O_DIRECT restrictions). It achieves this for reads
> by rounding the request to host-side block boundary, and for writes by
> performing a read-modify-write cycle (and serialising requests
> touching the same block so that the RMW doesn't write back stale data).

Nice, this might really help on s390 (also for KVM) since dasd disks usually
have a 4k sector size. We also have flash systems with 4k block size. Both
disk systems cause lots of trouble with cache=none and friends.

Do you have a tree with these patches, so that I can test those on s390?



> 
> Originally I intended to reuse a lot of code from Paolo's previous
> patch series, however as I tried to integrate pread/pwrite, which
> already do a very similar thing (except for considering concurrency),
> and because I wanted to implement zero-copy, most of this series ended
> up being new code.
> 
> Zero-copy is possible in a common case because while XFS defauls to a
> 4k sector size and therefore 4k on-disk O_DIRECT alignment for 512E
> disks, it still only has a 512 byte memory alignment requirement.
> (Unfortunately the XFS_IOC_DIOINFO ioctl claims 4k even for memory, but
> we know that the value is wrong and can probe it.)
> 
> 
> Changes in v2 -> v3:
> - Fixed I/O throttling bypass by converting to byte granularity [Wenchao]
> - Made 'bytes' argument to tracked_request_overlaps() unsigned [Max]
> - Fixed a corruption bug that came from using outdated RMW buffers after
>   waiting for another request and added some assertions to check the
>   assumptions [Peter]
> - Fixed bytes vs. sectors error in zero-after-EOF code of
>   bdrv_co_do_preadv [Max]
> - Removed orphaned protoype in block.h [Max]
> - A qemu-iotests case and some infrastructure to support it
> 
> Changes in v1 -> v2:
> - Fixed overlap_bytes calculation in mark_request_serialising()
> - Fixed wait_serialising_requests() deadlock
> - iscsi: Set bs->request_alignment [Peter]
> - iscsi: Query block limits only in iscsi_open() when no other request
>   are in flight, and in iscsi_refresh_limits() copy the stored values
>   into bs->bl [Peter]
> 
> Changes in RFC -> v1:
> - Moved opt_mem_alignment into BlockLimits [Paolo]
> - Changed BlockLimits in turn to work a bit more like the
>   .bdrv_opt_mem_align() callback of the RFC; allows updating the
>   BlockLimits later when the chain changes or bdrv_reopen() toggles
>   O_DIRECT
> - Fixed a typo in a commit message [Eric]
> 
> 
> Kevin Wolf (26):
>   block: Move initialisation of BlockLimits to bdrv_refresh_limits()
>   block: Inherit opt_transfer_length
>   block: Update BlockLimits when they might have changed
>   qemu_memalign: Allow small alignments
>   block: Detect unaligned length in bdrv_qiov_is_aligned()
>   block: Don't use guest sector size for qemu_blockalign()
>   block: Introduce bdrv_aligned_preadv()
>   block: Introduce bdrv_co_do_preadv()
>   block: Introduce bdrv_aligned_pwritev()
>   block: write: Handle COR dependency after I/O throttling
>   block: Introduce bdrv_co_do_pwritev()
>   block: Switch BdrvTrackedRequest to byte granularity
>   block: Allow waiting for overlapping requests between begin/end
>   block: Make zero-after-EOF work with larger alignment
>   block: Generalise and optimise COR serialisation
>   block: Make overlap range for serialisation dynamic
>   block: Allow wait_serialising_requests() at any point
>   block: Align requests in bdrv_co_do_pwritev()
>   block: Assert serialisation assumptions in pwritev
>   block: Change coroutine wrapper to byte granularity
>   block: Make bdrv_pread() a bdrv_prwv_co() wrapper
>   block: Make bdrv_pwrite() a bdrv_prwv_co() wrapper
>   blkdebug: Make required alignment configurable
>   qemu-io: New command 'sleep'
>   qemu-iotests: Test pwritev RMW logic
>   block: Switch bdrv_io_limits_intercept() to byte granularity
> 
> Paolo Bonzini (3):
>   block: rename buffer_alignment to guest_block_size
>   raw: Probe required direct I/O alignment
>   iscsi: Set bs->request_alignment
> 
>  block.c                    | 644 
> +++++++++++++++++++++++++++++++--------------
>  block/backup.c             |   7 +-
>  block/blkdebug.c           |  24 ++
>  block/iscsi.c              |  47 ++--
>  block/qcow2.c              |  11 +-
>  block/qed.c                |  11 +-
>  block/raw-posix.c          | 102 +++++--
>  block/raw-win32.c          |  41 +++
>  block/stream.c             |   2 +
>  block/vmdk.c               |  22 +-
>  hw/block/virtio-blk.c      |   2 +-
>  hw/ide/core.c              |   2 +-
>  hw/scsi/scsi-disk.c        |   2 +-
>  hw/scsi/scsi-generic.c     |   2 +-
>  include/block/block.h      |  15 +-
>  include/block/block_int.h  |  27 +-
>  qemu-io-cmds.c             |  42 +++
>  tests/qemu-iotests/077     | 278 +++++++++++++++++++
>  tests/qemu-iotests/077.out | 202 ++++++++++++++
>  tests/qemu-iotests/group   |   1 +
>  util/oslib-posix.c         |   5 +
>  21 files changed, 1234 insertions(+), 255 deletions(-)
>  create mode 100755 tests/qemu-iotests/077
>  create mode 100644 tests/qemu-iotests/077.out
>