Re: [PATCH v2 1/6] block: add blk_io_plug_call() API

[Stefano Garzarella <sgarzare@xxxxxxxxxx>]

On Tue, May 23, 2023 at 01:12:55PM -0400, Stefan Hajnoczi wrote:
> Introduce a new API for thread-local blk_io_plug() that does not
> traverse the block graph. The goal is to make blk_io_plug() multi-queue
> friendly.
>
> Instead of having block drivers track whether or not we're in a plugged
> section, provide an API that allows them to defer a function call until
> we're unplugged: blk_io_plug_call(fn, opaque). If blk_io_plug_call() is
> called multiple times with the same fn/opaque pair, then fn() is only
> called once at the end of the function - resulting in batching.
>
> This patch introduces the API and changes blk_io_plug()/blk_io_unplug().
> blk_io_plug()/blk_io_unplug() no longer require a BlockBackend argument
> because the plug state is now thread-local.
>
> Later patches convert block drivers to blk_io_plug_call() and then we
> can finally remove .bdrv_co_io_plug() once all block drivers have been
> converted.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
> ---
> v2
> - "is not be freed" -> "is not freed" [Eric]
> ---
> MAINTAINERS                       |   1 +
> include/sysemu/block-backend-io.h |  13 +--
> block/block-backend.c             |  22 -----
> block/plug.c                      | 159 ++++++++++++++++++++++++++++++
> hw/block/dataplane/xen-block.c    |   8 +-
> hw/block/virtio-blk.c             |   4 +-
> hw/scsi/virtio-scsi.c             |   6 +-
> block/meson.build                 |   1 +
> 8 files changed, 173 insertions(+), 41 deletions(-)
> create mode 100644 block/plug.c
Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>