[Qemu-devel] [PATCH 06/13] AioContext: introduce aio_attach_aio_bs() and its pair

[Ming Lei <ming.lei@canonical.com>]

This patch introduces aio_attach_aio_bs() and its pair
for supporting IO submission as batch in AioContext wide,
and one typical use case is multi-lun SCSI.

aio_attach_aio_bs() will attach one 'bs' which is capable
of IO submission as batch, then all I/O submission in
this AioContext will borrow the io queue from this 'bs',
so that we can maximum IO submission as batch.

aio_detach_aio_bs() will detach the 'bs' when all 'bs'
in the AioContext is detached.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 async.c             |    1 +
 include/block/aio.h |   27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/async.c b/async.c
index 6e1b282..0f4b530 100644
--- a/async.c
+++ b/async.c
@@ -305,6 +305,7 @@ AioContext *aio_context_new(Error **errp)
                            event_notifier_test_and_clear);
     ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
     ctx->thread_pool = NULL;
+    ctx->bs_refcnt = 0;
     qemu_mutex_init(&ctx->bh_lock);
     rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
diff --git a/include/block/aio.h b/include/block/aio.h
index 6bf0e04..e34a21f 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -90,6 +90,11 @@ struct AioContext {
 
     /* TimerLists for calling timers - one per clock type */
     QEMUTimerListGroup tlg;
+
+    /* IO submit as batch in AioContext wide */
+    BlockDriverState *master_aio_bs;
+    int bs_refcnt;
+    void *opaque;
 };
 
 /* Used internally to synchronize aio_poll against qemu_bh_schedule.  */
@@ -325,4 +330,26 @@ static inline void aio_timer_init(AioContext *ctx,
  */
 int64_t aio_compute_timeout(AioContext *ctx);
 
+static inline bool aio_attach_aio_bs(AioContext *ctx,
+                                     BlockDriverState *bs)
+{
+    if (!ctx->bs_refcnt++) {
+        ctx->master_aio_bs = bs;
+        return true;
+    }
+
+    return false;
+}
+
+static inline bool aio_detach_aio_bs(AioContext *ctx,
+                                     BlockDriverState *bs)
+{
+    if (!--ctx->bs_refcnt) {
+        ctx->master_aio_bs = NULL;
+        return true;
+    }
+
+    return false;
+}
+
 #endif
-- 
1.7.9.5