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Re: [Qemu-devel] [PATCH v5 0/8] New block driver: blklogwrites

From: Ari Sundholm
Subject: Re: [Qemu-devel] [PATCH v5 0/8] New block driver: blklogwrites
Date: Tue, 26 Jun 2018 21:06:33 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0

Just a weekly ping. Any comments appreciated.

On 06/19/2018 04:43 PM, Ari Sundholm wrote:
This patch series adds a new block driver, blklogwrites, to QEMU. The
driver is given two block devices: a raw device backed by an image or a
host block device, and a log device, typically backed by a file, on
which writes to the raw device are logged.

The logging format used is the same as in the dm-log-writes target of
the Linux kernel device mapper. The log reflects the writes that have
been performed on the guest block device and flushed. To be strict, the
log may contain writes that have not been flushed yet, but they are
technically outside the bounds of the log until the next flush updates
the metadata in the log superblock. We believe these semantics to be
useful even though they may not be completely identical to those of

This functionality can be used for crash consistency and fs consistency
testing in filesystem drivers, including on non-Linux guests and older
guests running Linux versions without support for dm-log-writes. This
is simple and useful. Admittedly this and more advanced things could
perhaps be done by extending the quorum driver, but this approach would
require re-engineering the functionality and involve a more complicated
setup, so we offer this simple solution which we have found useful

In the first patch of this series, two block permission constants are
moved from block.c to include/block/block.h to make them available
outside of block.c. The next patch uses these constants.

In patches 2-7, a mechanism to pass the block configuration of a block
backend to a block driver is introduced, and this mechanism is
integrated in various hw/block drivers.

In patch 8, the blklogwrites driver is introduced. The driver uses the
mechanism from the previous patches to align all requests to the
logical sector size of the underlying block backend of the guest block
device being logged and use that size as a basis for offsets and sizes
in the log entries. This means that the sector size in the log metadata
will be set to the logical sector size, and offsets and sizes of writes
will be expressed as a multiple of that.

   - Reorder patches and squash blklogwrites driver patches together
   - Rebase on current upstream master
   - No functional changes

   - Check return value of snprintf() (flagged by patchew)
   - Don't use C99 for loop initial declaration (flagged by patchew, but
     wasn't QEMU supposed to be C99? Oh well.)
   - Add proper "Since" fields for blklogwrites in block-core.json
   - Rebase on current upstream master

   - Rebase on current upstream master

   - Incorporate review feedback
   - Add patches to apply block configurations in more block device

*** BLURB HERE ***

Aapo Vienamo (1):
   block: Add blklogwrites

Ari Sundholm (7):
   block: Move two block permission constants to the relevant enum
   block: Add a mechanism for passing a block driver a block
   hw/scsi/scsi-disk: Always apply block configuration to block driver
   hw/ide/qdev: Always apply block configuration to block driver
   hw/block/virtio-blk: Always apply block configuration to block driver
   hw/block/nvme: Always apply block configuration to block driver
   hw/block/fdc: Always apply block configuration to block driver

  MAINTAINERS               |   6 +
  block.c                   |   6 -
  block/Makefile.objs       |   1 +
  block/blklogwrites.c      | 426 ++++++++++++++++++++++++++++++++++++++++++++++
  block/io.c                |  22 +++
  hw/block/block.c          |  12 +-
  hw/block/fdc.c            |   4 +
  hw/block/nvme.c           |   1 +
  hw/block/virtio-blk.c     |   1 +
  hw/ide/qdev.c             |   2 +
  hw/scsi/scsi-disk.c       |   1 +
  include/block/block.h     |  17 ++
  include/block/block_int.h |   9 +
  include/hw/block/block.h  |   1 +
  qapi/block-core.json      |  30 +++-
  15 files changed, 526 insertions(+), 13 deletions(-)
  create mode 100644 block/blklogwrites.c

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