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io: make qio_channel_yield aware of AioContexts

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Support separate coroutines for reading and writing, and place the
read/write handlers on the AioContext that the QIOChannel is registered
with.

Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20170213135235.12274-7-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Paolo Bonzini 2017-02-13 14:52:23 +01:00 committed by Stefan Hajnoczi
parent bf88c1247f
commit c4c497d27f
2 changed files with 110 additions and 25 deletions
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47
include/io/channel.h
View file

@ -23,6 +23,7 @@
#include "qemu-common.h"
#include "qom/object.h"
#include "qemu/coroutine.h"
#include "block/aio.h"
#define TYPE_QIO_CHANNEL "qio-channel"
@ -81,6 +82,9 @@ struct QIOChannel {
Object parent;
unsigned int features; /* bitmask of QIOChannelFeatures */
char *name;
AioContext *ctx;
Coroutine *read_coroutine;
Coroutine *write_coroutine;
#ifdef _WIN32
HANDLE event; /* For use with GSource on Win32 */
#endif
@ -502,14 +506,51 @@ guint qio_channel_add_watch(QIOChannel *ioc,
GDestroyNotify notify);
/**
* qio_channel_attach_aio_context:
* @ioc: the channel object
* @ctx: the #AioContext to set the handlers on
*
* Request that qio_channel_yield() sets I/O handlers on
* the given #AioContext. If @ctx is %NULL, qio_channel_yield()
* uses QEMU's main thread event loop.
*
* You can move a #QIOChannel from one #AioContext to another even if
* I/O handlers are set for a coroutine. However, #QIOChannel provides
* no synchronization between the calls to qio_channel_yield() and
* qio_channel_attach_aio_context().
*
* Therefore you should first call qio_channel_detach_aio_context()
* to ensure that the coroutine is not entered concurrently. Then,
* while the coroutine has yielded, call qio_channel_attach_aio_context(),
* and then aio_co_schedule() to place the coroutine on the new
* #AioContext. The calls to qio_channel_detach_aio_context()
* and qio_channel_attach_aio_context() should be protected with
* aio_context_acquire() and aio_context_release().
*/
void qio_channel_attach_aio_context(QIOChannel *ioc,
AioContext *ctx);
/**
* qio_channel_detach_aio_context:
* @ioc: the channel object
*
* Disable any I/O handlers set by qio_channel_yield(). With the
* help of aio_co_schedule(), this allows moving a coroutine that was
* paused by qio_channel_yield() to another context.
*/
void qio_channel_detach_aio_context(QIOChannel *ioc);
/**
* qio_channel_yield:
* @ioc: the channel object
* @condition: the I/O condition to wait for
*
* Yields execution from the current coroutine until
* the condition indicated by @condition becomes
* available.
* Yields execution from the current coroutine until the condition
* indicated by @condition becomes available. @condition must
* be either %G_IO_IN or %G_IO_OUT; it cannot contain both. In
* addition, no two coroutine can be waiting on the same condition
* and channel at the same time.
*
* This must only be called from coroutine context
*/

88
io/channel.c
View file

@ -21,7 +21,7 @@
#include "qemu/osdep.h"
#include "io/channel.h"
#include "qapi/error.h"
#include "qemu/coroutine.h"
#include "qemu/main-loop.h"
bool qio_channel_has_feature(QIOChannel *ioc,
QIOChannelFeature feature)
@ -238,36 +238,80 @@ off_t qio_channel_io_seek(QIOChannel *ioc,
}
typedef struct QIOChannelYieldData QIOChannelYieldData;
struct QIOChannelYieldData {
QIOChannel *ioc;
Coroutine *co;
};
static void qio_channel_set_aio_fd_handlers(QIOChannel *ioc);
static gboolean qio_channel_yield_enter(QIOChannel *ioc,
GIOCondition condition,
gpointer opaque)
static void qio_channel_restart_read(void *opaque)
{
QIOChannelYieldData *data = opaque;
qemu_coroutine_enter(data->co);
return FALSE;
QIOChannel *ioc = opaque;
Coroutine *co = ioc->read_coroutine;
ioc->read_coroutine = NULL;
qio_channel_set_aio_fd_handlers(ioc);
aio_co_wake(co);
}
static void qio_channel_restart_write(void *opaque)
{
QIOChannel *ioc = opaque;
Coroutine *co = ioc->write_coroutine;
ioc->write_coroutine = NULL;
qio_channel_set_aio_fd_handlers(ioc);
aio_co_wake(co);
}
static void qio_channel_set_aio_fd_handlers(QIOChannel *ioc)
{
IOHandler *rd_handler = NULL, *wr_handler = NULL;
AioContext *ctx;
if (ioc->read_coroutine) {
rd_handler = qio_channel_restart_read;
}
if (ioc->write_coroutine) {
wr_handler = qio_channel_restart_write;
}
ctx = ioc->ctx ? ioc->ctx : iohandler_get_aio_context();
qio_channel_set_aio_fd_handler(ioc, ctx, rd_handler, wr_handler, ioc);
}
void qio_channel_attach_aio_context(QIOChannel *ioc,
AioContext *ctx)
{
AioContext *old_ctx;
if (ioc->ctx == ctx) {
return;
}
old_ctx = ioc->ctx ? ioc->ctx : iohandler_get_aio_context();
qio_channel_set_aio_fd_handler(ioc, old_ctx, NULL, NULL, NULL);
ioc->ctx = ctx;
qio_channel_set_aio_fd_handlers(ioc);
}
void qio_channel_detach_aio_context(QIOChannel *ioc)
{
ioc->read_coroutine = NULL;
ioc->write_coroutine = NULL;
qio_channel_set_aio_fd_handlers(ioc);
ioc->ctx = NULL;
}
void coroutine_fn qio_channel_yield(QIOChannel *ioc,
GIOCondition condition)
{
QIOChannelYieldData data;
assert(qemu_in_coroutine());
data.ioc = ioc;
data.co = qemu_coroutine_self();
qio_channel_add_watch(ioc,
condition,
qio_channel_yield_enter,
&data,
NULL);
if (condition == G_IO_IN) {
assert(!ioc->read_coroutine);
ioc->read_coroutine = qemu_coroutine_self();
} else if (condition == G_IO_OUT) {
assert(!ioc->write_coroutine);
ioc->write_coroutine = qemu_coroutine_self();
} else {
abort();
}
qio_channel_set_aio_fd_handlers(ioc);
qemu_coroutine_yield();
}