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block: Allow AIO_WAIT_WHILE with NULL ctx 

bdrv_drain_all() wants to have a single polling loop for draining the
in-flight requests of all nodes. This means that the AIO_WAIT_WHILE()
condition relies on activity in multiple AioContexts, which is polled
from the mainloop context. We must therefore call AIO_WAIT_WHILE() from
the mainloop thread and use the AioWait notification mechanism.

Just randomly picking the AioContext of any non-mainloop thread would
work, but instead of bothering to find such a context in the caller, we
can just as well accept NULL for ctx.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2018-04-10 15:51:52 +02:00
parent 57320ca961
commit 4d22bbf4ef
1 changed files with 9 additions and 4 deletions
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13
include/block/aio-wait.h
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@ -57,7 +57,8 @@ typedef struct {
/** /**
* AIO_WAIT_WHILE: * AIO_WAIT_WHILE:
* @wait: the aio wait object * @wait: the aio wait object
* @ctx: the aio context * @ctx: the aio context, or NULL if multiple aio contexts (for which the
* caller does not hold a lock) are involved in the polling condition.
* @cond: wait while this conditional expression is true * @cond: wait while this conditional expression is true
* *
* Wait while a condition is true. Use this to implement synchronous * Wait while a condition is true. Use this to implement synchronous
@ -75,7 +76,7 @@ typedef struct {
bool waited_ = false; \ bool waited_ = false; \
AioWait *wait_ = (wait); \ AioWait *wait_ = (wait); \
AioContext *ctx_ = (ctx); \ AioContext *ctx_ = (ctx); \
if (in_aio_context_home_thread(ctx_)) { \ if (ctx_ && in_aio_context_home_thread(ctx_)) { \
while ((cond)) { \ while ((cond)) { \
aio_poll(ctx_, true); \ aio_poll(ctx_, true); \
waited_ = true; \ waited_ = true; \
@ -86,9 +87,13 @@ typedef struct {
/* Increment wait_->num_waiters before evaluating cond. */ \ /* Increment wait_->num_waiters before evaluating cond. */ \
atomic_inc(&wait_->num_waiters); \ atomic_inc(&wait_->num_waiters); \
while ((cond)) { \ while ((cond)) { \
aio_context_release(ctx_); \ if (ctx_) { \
aio_context_release(ctx_); \
} \
aio_poll(qemu_get_aio_context(), true); \ aio_poll(qemu_get_aio_context(), true); \
aio_context_acquire(ctx_); \ if (ctx_) { \
aio_context_acquire(ctx_); \
} \
waited_ = true; \ waited_ = true; \
} \ } \
atomic_dec(&wait_->num_waiters); \ atomic_dec(&wait_->num_waiters); \