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aio: document locking

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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>
This commit is contained in:
Paolo Bonzini 2017-01-12 19:07:59 +01:00 • committed by Stefan Hajnoczi
parent b92d9a91ab
commit 7c690fd193
2 changed files with 21 additions and 24 deletions
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32
include/block/aio.h
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@ -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);