[Qemu-devel] [PATCH 00/22] block: Support for 512b-on-4k emulation

[Kevin Wolf <kwolf@redhat.com>]

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).

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 since RFC:
- 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 (20):
  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: Align requests in bdrv_co_do_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

Paolo Bonzini (2):
  block: rename buffer_alignment to guest_block_size
  raw: Probe required direct I/O alignment

 block.c                   | 602 +++++++++++++++++++++++++++++++---------------
 block/backup.c            |   7 +-
 block/iscsi.c             |  87 ++++---
 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     |   6 +-
 include/block/block_int.h |  25 +-
 util/oslib-posix.c        |   5 +
 16 files changed, 666 insertions(+), 263 deletions(-)

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1.8.1.4