aio: add a ThreadPool instance to AioContext

This patch adds a ThreadPool to AioContext.  It's possible that some
AioContext instances will never use the ThreadPool, so defer creation
until aio_get_thread_pool().

The reason why AioContext should have the ThreadPool is because the
ThreadPool is bound to a AioContext instance where the work item's
callback function is invoked.  It doesn't make sense to keep the
ThreadPool pointer anywhere other than AioContext.  For example,
block/raw-posix.c can get its AioContext's ThreadPool and submit work.

Special note about headers: I used struct ThreadPool in aio.h because
there is a circular dependency if aio.h includes thread-pool.h.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/block/aio.h b/include/block/aio.h
index 5b54d383fc..183679374f 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -66,6 +66,9 @@ typedef struct AioContext {
 
     /* GPollFDs for aio_poll() */
     GArray *pollfds;
+
+    /* Thread pool for performing work and receiving completion callbacks */
+    struct ThreadPool *thread_pool;
 } AioContext;
 
 /* Returns 1 if there are still outstanding AIO requests; 0 otherwise */
@@ -223,6 +226,9 @@ void aio_set_event_notifier(AioContext *ctx,
  */
 GSource *aio_get_g_source(AioContext *ctx);
 
+/* Return the ThreadPool bound to this AioContext */
+struct ThreadPool *aio_get_thread_pool(AioContext *ctx);
+
 /* Functions to operate on the main QEMU AioContext.  */
 
 bool qemu_aio_wait(void);