Re: [PATCH v6 2/4] block: introduce zone append write for zoned devices

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Fri, Mar 10, 2023 at 06:31:04PM +0800, Sam Li wrote:
> A zone append command is a write operation that specifies the first
> logical block of a zone as the write position. When writing to a zoned
> block device using zone append, the byte offset of writes is pointing
> to the write pointer of that zone. Upon completion the device will
> respond with the position the data has been written in the zone.
> 
> Signed-off-by: Sam Li <faithilikerun@gmail.com>
> ---
>  block/block-backend.c             | 60 +++++++++++++++++++++++++++++++
>  block/file-posix.c                | 54 +++++++++++++++++++++++++---
>  block/io.c                        | 21 +++++++++++
>  block/io_uring.c                  |  4 +++
>  block/linux-aio.c                 |  3 ++
>  block/raw-format.c                |  8 +++++
>  include/block/block-io.h          |  4 +++
>  include/block/block_int-common.h  |  5 +++
>  include/block/raw-aio.h           |  4 ++-
>  include/sysemu/block-backend-io.h |  9 +++++
>  10 files changed, 166 insertions(+), 6 deletions(-)
> 
> diff --git a/block/block-backend.c b/block/block-backend.c
> index f70b08e3f6..28e8f5d778 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -1888,6 +1888,45 @@ BlockAIOCB *blk_aio_zone_mgmt(BlockBackend *blk, BlockZoneOp op,
>      return &acb->common;
>  }
>  
> +static void coroutine_fn blk_aio_zone_append_entry(void *opaque)
> +{
> +    BlkAioEmAIOCB *acb = opaque;
> +    BlkRwCo *rwco = &acb->rwco;
> +
> +    rwco->ret = blk_co_zone_append(rwco->blk, &acb->bytes,
> +                                   rwco->iobuf, rwco->flags);
> +    blk_aio_complete(acb);
> +}
> +
> +BlockAIOCB *blk_aio_zone_append(BlockBackend *blk, int64_t *offset,
> +                                QEMUIOVector *qiov, BdrvRequestFlags flags,
> +                                BlockCompletionFunc *cb, void *opaque) {
> +    BlkAioEmAIOCB *acb;
> +    Coroutine *co;
> +    IO_CODE();
> +
> +    blk_inc_in_flight(blk);
> +    acb = blk_aio_get(&blk_aio_em_aiocb_info, blk, cb, opaque);
> +    acb->rwco = (BlkRwCo) {
> +        .blk    = blk,
> +        .ret    = NOT_DONE,
> +        .flags  = flags,
> +        .iobuf  = qiov,
> +    };
> +    acb->bytes = *offset;
> +    acb->has_returned = false;
> +
> +    co = qemu_coroutine_create(blk_aio_zone_append_entry, acb);
> +    aio_co_enter(blk_get_aio_context(blk), co);
> +    acb->has_returned = true;
> +    if (acb->rwco.ret != NOT_DONE) {
> +        replay_bh_schedule_oneshot_event(blk_get_aio_context(blk),
> +                                         blk_aio_complete_bh, acb);
> +    }
> +
> +    return &acb->common;
> +}

How is the resulting offset value communicated back to the caller? I
see offset being read (dereferenced) but there is no write (assignment).
Maybe this function should pass through acb->bytes = (int64_t)offset
instead so that blk_co_zone_append() can modify the offset?

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