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authorStefan Hajnoczi <stefanha@redhat.com>2014-03-03 11:30:04 +0100
committerStefan Hajnoczi <stefanha@redhat.com>2014-03-13 14:42:24 +0100
commit98563fc3ec44c1becce6f1720ad6b0a82ed101b4 (patch)
tree18adf9c0239707158d5f95ef2e0702c5eeaa29b8 /include/block
parent2da61b671eb89fcaa306738f44eed472977d6587 (diff)
aio: add aio_context_acquire() and aio_context_release()
It can be useful to run an AioContext from a thread which normally does not "own" the AioContext. For example, request draining can be implemented by acquiring the AioContext and looping aio_poll() until all requests have been completed. The following pattern should work: /* Event loop thread */ while (running) { aio_context_acquire(ctx); aio_poll(ctx, true); aio_context_release(ctx); } /* Another thread */ aio_context_acquire(ctx); bdrv_read(bs, 0x1000, buf, 1); aio_context_release(ctx); This patch implements aio_context_acquire() and aio_context_release(). Note that existing aio_poll() callers do not need to worry about acquiring and releasing - it is only needed when multiple threads will call aio_poll() on the same AioContext. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'include/block')
-rw-r--r--include/block/aio.h18
1 files changed, 18 insertions, 0 deletions
diff --git a/include/block/aio.h b/include/block/aio.h
index 2efdf416cf..a92511bd3b 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -19,6 +19,7 @@
#include "qemu/queue.h"
#include "qemu/event_notifier.h"
#include "qemu/thread.h"
+#include "qemu/rfifolock.h"
#include "qemu/timer.h"
typedef struct BlockDriverAIOCB BlockDriverAIOCB;
@@ -47,6 +48,9 @@ typedef void IOHandler(void *opaque);
struct AioContext {
GSource source;
+ /* Protects all fields from multi-threaded access */
+ RFifoLock lock;
+
/* The list of registered AIO handlers */
QLIST_HEAD(, AioHandler) aio_handlers;
@@ -104,6 +108,20 @@ void aio_context_ref(AioContext *ctx);
*/
void aio_context_unref(AioContext *ctx);
+/* Take ownership of the AioContext. If the AioContext will be shared between
+ * threads, a thread must have ownership when calling aio_poll().
+ *
+ * Note that multiple threads calling aio_poll() means timers, BHs, and
+ * callbacks may be invoked from a different thread than they were registered
+ * from. Therefore, code must use AioContext acquire/release or use
+ * fine-grained synchronization to protect shared state if other threads will
+ * be accessing it simultaneously.
+ */
+void aio_context_acquire(AioContext *ctx);
+
+/* Relinquish ownership of the AioContext. */
+void aio_context_release(AioContext *ctx);
+
/**
* aio_bh_new: Allocate a new bottom half structure.
*