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authorPaolo Bonzini <pbonzini@redhat.com>2017-01-12 19:07:59 +0100
committerStefan Hajnoczi <stefanha@redhat.com>2017-01-16 13:25:18 +0000
commit7c690fd1931f0908b18f7034b5d71d7b27ca59ef (patch)
treefdc01d4b37919eb554fa3ed65d54138694f9ed58 /include
parentb92d9a91abae1569ac499f72fbb90ee7b0ae5398 (diff)
aio: document locking
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Message-id: 20170112180800.21085-10-pbonzini@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'include')
-rw-r--r--include/block/aio.h32
1 files changed, 16 insertions, 16 deletions
diff --git a/include/block/aio.h b/include/block/aio.h
index be3adfec43..7df271d2b9 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -53,18 +53,12 @@ struct LinuxAioState;
struct AioContext {
GSource source;
- /* Protects all fields from multi-threaded access */
+ /* Used by AioContext users to protect from multi-threaded access. */
QemuRecMutex lock;
- /* The list of registered AIO handlers */
+ /* The list of registered AIO handlers. Protected by ctx->list_lock. */
QLIST_HEAD(, AioHandler) aio_handlers;
- /* This is a simple lock used to protect the aio_handlers list.
- * Specifically, it's used to ensure that no callbacks are removed while
- * we're walking and dispatching callbacks.
- */
- int walking_handlers;
-
/* Used to avoid unnecessary event_notifier_set calls in aio_notify;
* accessed with atomic primitives. If this field is 0, everything
* (file descriptors, bottom halves, timers) will be re-evaluated
@@ -90,9 +84,9 @@ struct AioContext {
*/
uint32_t notify_me;
- /* A lock to protect between bh's adders and deleter, and to ensure
- * that no callbacks are removed while we're walking and dispatching
- * them.
+ /* A lock to protect between QEMUBH and AioHandler adders and deleter,
+ * and to ensure that no callbacks are removed while we're walking and
+ * dispatching them.
*/
QemuLockCnt list_lock;
@@ -114,7 +108,9 @@ struct AioContext {
bool notified;
EventNotifier notifier;
- /* Thread pool for performing work and receiving completion callbacks */
+ /* Thread pool for performing work and receiving completion callbacks.
+ * Has its own locking.
+ */
struct ThreadPool *thread_pool;
#ifdef CONFIG_LINUX_AIO
@@ -124,7 +120,9 @@ struct AioContext {
struct LinuxAioState *linux_aio;
#endif
- /* TimerLists for calling timers - one per clock type */
+ /* TimerLists for calling timers - one per clock type. Has its own
+ * locking.
+ */
QEMUTimerListGroup tlg;
int external_disable_cnt;
@@ -178,9 +176,11 @@ void aio_context_unref(AioContext *ctx);
* automatically takes care of calling aio_context_acquire and
* aio_context_release.
*
- * Access to timers and BHs from a thread that has not acquired AioContext
- * is possible. Access to callbacks for now must be done while the AioContext
- * is owned by the thread (FIXME).
+ * Note that this is separate from bdrv_drained_begin/bdrv_drained_end. A
+ * thread still has to call those to avoid being interrupted by the guest.
+ *
+ * Bottom halves, timers and callbacks can be created or removed without
+ * acquiring the AioContext.
*/
void aio_context_acquire(AioContext *ctx);