Re: [Qemu-devel] [PATCH v2 00/11] block: allow blockjobs to coexist with dataplane

[Stefan Hajnoczi]

On Tue, Oct 21, 2014 at 12:03:49PM +0100, Stefan Hajnoczi wrote:
> v2:
>  * Protect block_job_defer_to_main_loop_bh() against AioContext change [Max]
>  * Drop unnecessary if (buf) around qemu_vfree(buf) [Max]
> 
> Almost all the infrastructure is in place to make blockjobs safe for use with
> dataplane:
> 
>   * Op blockers all us to exclude commands that could conflict with a blockjob
>     or dataplane.
> 
>   * AioContext acquire/release allows threads to temporarily access a
>     BlockDriverState that is running in another thread.
> 
> This series introduces a few additional helpers:
> 
>   * block_job_defer_to_main_loop() which allows blockjobs to run their
>     completion code in the QEMU main loop.  This is necessary because some
>     operations are not safe outside the QEMU global mutex.
> 
>   * bdrv_drain() which can be used in limited cases to wait for in-flight
>     requests to complete (as opposed to the global bdrv_drain_all() function).
> 
> The approach taken in this series is to convert the blockdev.c monitor command
> so it acquires the BlockDriverState's AioContext.  Normally only 1 AioContext
> is involved at a time but the mirror job's to_replace argument can involve a
> second AioContext.
> 
> Then the block job code itself is converted to defer main loop code using
> block_job_defer_to_main_loop().
> 
> Example:
> 
>   $ qemu-system-x86_64 -enable-kvm -m 1024 \
>         -drive if=none,id=drive0,file=test.img \
>         -object iothread,iothread0 \
>         -device virtio-blk-pci,drive=drive0,iothread=iothread0
>   (qemu) drive_mirror drive0 test2.img
> 
> Stefan Hajnoczi (11):
>   block: acquire AioContext in generic blockjob QMP commands
>   blockdev: acquire AioContext in do_qmp_query_block_jobs_one()
>   blockdev: acquire AioContext in blockdev_mark_auto_del()
>   blockdev: add note that block_job_cb() must be thread-safe
>   blockjob: add block_job_defer_to_main_loop()
>   block: add bdrv_drain()
>   block: let backup blockjob run in BDS AioContext
>   block: let stream blockjob run in BDS AioContext
>   block: let mirror blockjob run in BDS AioContext
>   block: let commit blockjob run in BDS AioContext
>   block: declare blockjobs and dataplane friends!
> 
>  block.c                         |  49 +++++++++--
>  block/backup.c                  |  21 ++++-
>  block/commit.c                  |  70 ++++++++++------
>  block/mirror.c                  |  85 +++++++++++++------
>  block/stream.c                  |  50 +++++++----
>  blockdev.c                      | 179 
> +++++++++++++++++++++++++++++-----------
>  blockjob.c                      |  46 +++++++++++
>  hw/block/dataplane/virtio-blk.c |   5 ++
>  include/block/block.h           |   1 +
>  include/block/blockjob.h        |  19 +++++
>  10 files changed, 402 insertions(+), 123 deletions(-)

Applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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