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[Qemu-devel] [PATCH 3/3] nbd: do not block on partial reply header reads
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 3/3] nbd: do not block on partial reply header reads |
Date: |
Fri, 23 Dec 2016 19:26:41 +0100 |
Read the replies from a coroutine. qio_channel_yield is used so that
the right coroutine is restarted automatically, eliminating the need
for send_coroutine in NBDClientSession.
Signed-off-by: Paolo Bonzini <address@hidden>
---
block/nbd-client.c | 108 +++++++++++++++++++++--------------------------------
1 file changed, 42 insertions(+), 66 deletions(-)
diff --git a/block/nbd-client.c b/block/nbd-client.c
index 06f1532..a3c2c19 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -33,8 +33,9 @@
#define HANDLE_TO_INDEX(bs, handle) ((handle) ^ ((uint64_t)(intptr_t)bs))
#define INDEX_TO_HANDLE(bs, index) ((index) ^ ((uint64_t)(intptr_t)bs))
-static void nbd_recv_coroutines_enter_all(NBDClientSession *s)
+static void nbd_recv_coroutines_enter_all(BlockDriverState *bs)
{
+ NBDClientSession *s = nbd_get_client_session(bs);
int i;
for (i = 0; i < MAX_NBD_REQUESTS; i++) {
@@ -42,6 +43,7 @@ static void nbd_recv_coroutines_enter_all(NBDClientSession *s)
qemu_coroutine_enter(s->recv_coroutine[i]);
}
}
+ BDRV_POLL_WHILE(bs, s->read_reply_co);
}
static void nbd_teardown_connection(BlockDriverState *bs)
@@ -56,7 +58,7 @@ static void nbd_teardown_connection(BlockDriverState *bs)
qio_channel_shutdown(client->ioc,
QIO_CHANNEL_SHUTDOWN_BOTH,
NULL);
- nbd_recv_coroutines_enter_all(client);
+ nbd_recv_coroutines_enter_all(bs);
nbd_client_detach_aio_context(bs);
object_unref(OBJECT(client->sioc));
@@ -65,54 +67,34 @@ static void nbd_teardown_connection(BlockDriverState *bs)
client->ioc = NULL;
}
-static void nbd_reply_ready(void *opaque)
+static void nbd_read_reply_entry(void *opaque)
{
- BlockDriverState *bs = opaque;
- NBDClientSession *s = nbd_get_client_session(bs);
+ NBDClientSession *s = opaque;
uint64_t i;
int ret;
- if (!s->ioc) { /* Already closed */
- return;
- }
-
- if (s->reply.handle == 0) {
- /* No reply already in flight. Fetch a header. It is possible
- * that another thread has done the same thing in parallel, so
- * the socket is not readable anymore.
- */
+ for (;;) {
+ assert(s->reply.handle == 0);
ret = nbd_receive_reply(s->ioc, &s->reply);
- if (ret == -EAGAIN) {
- return;
- }
if (ret < 0) {
- s->reply.handle = 0;
- goto fail;
+ break;
}
- }
-
- /* There's no need for a mutex on the receive side, because the
- * handler acts as a synchronization point and ensures that only
- * one coroutine is called until the reply finishes. */
- i = HANDLE_TO_INDEX(s, s->reply.handle);
- if (i >= MAX_NBD_REQUESTS) {
- goto fail;
- }
- if (s->recv_coroutine[i]) {
- qemu_coroutine_enter(s->recv_coroutine[i]);
- return;
- }
-
-fail:
- nbd_teardown_connection(bs);
-}
+ /* There's no need for a mutex on the receive side, because the
+ * handler acts as a synchronization point and ensures that only
+ * one coroutine is called until the reply finishes.
+ */
+ i = HANDLE_TO_INDEX(s, s->reply.handle);
+ if (i >= MAX_NBD_REQUESTS || !s->recv_coroutine[i]) {
+ break;
+ }
-static void nbd_restart_write(void *opaque)
-{
- BlockDriverState *bs = opaque;
+ aio_co_wake(s->recv_coroutine[i]);
- qemu_coroutine_enter(nbd_get_client_session(bs)->send_coroutine);
+ /* We're woken up by the recv_coroutine itself. */
+ qemu_coroutine_yield();
+ }
+ s->read_reply_co = NULL;
}
static int nbd_co_send_request(BlockDriverState *bs,
@@ -120,7 +102,6 @@ static int nbd_co_send_request(BlockDriverState *bs,
QEMUIOVector *qiov)
{
NBDClientSession *s = nbd_get_client_session(bs);
- AioContext *aio_context;
int rc, ret, i;
qemu_co_mutex_lock(&s->send_mutex);
@@ -141,11 +122,6 @@ static int nbd_co_send_request(BlockDriverState *bs,
return -EPIPE;
}
- s->send_coroutine = qemu_coroutine_self();
- aio_context = bdrv_get_aio_context(bs);
-
- aio_set_fd_handler(aio_context, s->sioc->fd, false,
- nbd_reply_ready, nbd_restart_write, NULL, bs);
if (qiov) {
qio_channel_set_cork(s->ioc, true);
rc = nbd_send_request(s->ioc, request);
@@ -160,9 +136,6 @@ static int nbd_co_send_request(BlockDriverState *bs,
} else {
rc = nbd_send_request(s->ioc, request);
}
- aio_set_fd_handler(aio_context, s->sioc->fd, false,
- nbd_reply_ready, NULL, NULL, bs);
- s->send_coroutine = NULL;
qemu_co_mutex_unlock(&s->send_mutex);
return rc;
}
@@ -174,8 +147,7 @@ static void nbd_co_receive_reply(NBDClientSession *s,
{
int ret;
- /* Wait until we're woken up by the read handler. TODO: perhaps
- * peek at the next reply and avoid yielding if it's ours? */
+ /* Wait until we're woken up by nbd_read_reply_entry. */
qemu_coroutine_yield();
*reply = s->reply;
if (reply->handle != request->handle ||
@@ -209,14 +181,18 @@ static void nbd_coroutine_start(NBDClientSession *s,
/* s->recv_coroutine[i] is set as soon as we get the send_lock. */
}
-static void nbd_coroutine_end(NBDClientSession *s,
+static void nbd_coroutine_end(BlockDriverState *bs,
NBDRequest *request)
{
+ NBDClientSession *s = nbd_get_client_session(bs);
int i = HANDLE_TO_INDEX(s, request->handle);
+
s->recv_coroutine[i] = NULL;
- if (s->in_flight-- == MAX_NBD_REQUESTS) {
- qemu_co_queue_next(&s->free_sema);
- }
+
+ /* Kick the read_reply_co to get the next reply. */
+ aio_co_wake(s->read_reply_co);
+ s->in_flight--;
+ qemu_co_queue_next(&s->free_sema);
}
int nbd_client_co_preadv(BlockDriverState *bs, uint64_t offset,
@@ -241,7 +217,7 @@ int nbd_client_co_preadv(BlockDriverState *bs, uint64_t
offset,
} else {
nbd_co_receive_reply(client, &request, &reply, qiov);
}
- nbd_coroutine_end(client, &request);
+ nbd_coroutine_end(bs, &request);
return -reply.error;
}
@@ -271,7 +247,7 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t
offset,
} else {
nbd_co_receive_reply(client, &request, &reply, NULL);
}
- nbd_coroutine_end(client, &request);
+ nbd_coroutine_end(bs, &request);
return -reply.error;
}
@@ -306,7 +282,7 @@ int nbd_client_co_pwrite_zeroes(BlockDriverState *bs,
int64_t offset,
} else {
nbd_co_receive_reply(client, &request, &reply, NULL);
}
- nbd_coroutine_end(client, &request);
+ nbd_coroutine_end(bs, &request);
return -reply.error;
}
@@ -331,7 +307,7 @@ int nbd_client_co_flush(BlockDriverState *bs)
} else {
nbd_co_receive_reply(client, &request, &reply, NULL);
}
- nbd_coroutine_end(client, &request);
+ nbd_coroutine_end(bs, &request);
return -reply.error;
}
@@ -357,23 +333,23 @@ int nbd_client_co_pdiscard(BlockDriverState *bs, int64_t
offset, int count)
} else {
nbd_co_receive_reply(client, &request, &reply, NULL);
}
- nbd_coroutine_end(client, &request);
+ nbd_coroutine_end(bs, &request);
return -reply.error;
}
void nbd_client_detach_aio_context(BlockDriverState *bs)
{
- aio_set_fd_handler(bdrv_get_aio_context(bs),
- nbd_get_client_session(bs)->sioc->fd,
- false, NULL, NULL, NULL, NULL);
+ NBDClientSession *client = nbd_get_client_session(bs);
+ qio_channel_set_aio_context(QIO_CHANNEL(client->sioc), NULL);
}
void nbd_client_attach_aio_context(BlockDriverState *bs,
AioContext *new_context)
{
- aio_set_fd_handler(new_context, nbd_get_client_session(bs)->sioc->fd,
- false, nbd_reply_ready, NULL, NULL, bs);
+ NBDClientSession *client = nbd_get_client_session(bs);
+ qio_channel_set_aio_context(QIO_CHANNEL(client->sioc), new_context);
+ aio_co_schedule(new_context, client->read_reply_co);
}
void nbd_client_close(BlockDriverState *bs)
@@ -434,7 +410,7 @@ int nbd_client_init(BlockDriverState *bs,
/* Now that we're connected, set the socket to be non-blocking and
* kick the reply mechanism. */
qio_channel_set_blocking(QIO_CHANNEL(sioc), false, NULL);
-
+ client->read_reply_co = qemu_coroutine_create(nbd_read_reply_entry,
client);
nbd_client_attach_aio_context(bs, bdrv_get_aio_context(bs));
logout("Established connection with NBD server\n");
--
2.9.3