12.05.2017 18:46, Paolo Bonzini wrote:
On 12/05/2017 16:17, Vladimir Sementsov-Ogievskiy wrote:
nbd_wr_syncv is called either from coroutine or from client negotiation
code, when socket is in blocking mode. So, -EAGAIN is impossible.
Furthermore, EAGAIN is confusing, as, what to read/write again? With
EAGAIN as a return code we don't know how much data is already
read or written by the function, so in case of EAGAIN the whole
communication is broken.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---
Hi all!
If I understand right, nbd_wr_syncv is called either from coroutine
or from client negotiation code, when socket is in blocking mode.
So, some thoughts
1. let's establish this with an assert, because returning EAGAIN is
confusing (see above)
Yes, this seems like a good idea.
2. should we in case of non-coroutine context start this coroutine in
nbd_wr_syncv, like in bdrv_prwv_co, and use non-blocking mode?
3. is there any problems or disadvantages of moving client negotiation
to coroutine too?
When you move code to coroutines you need to be aware of what code can
now run concurrently, for example the monitor. I'm not sure that it's
possible to do this.
Hmm, can you please give some example of a problem? qcow2_open starts
coroutines to read it's header, why nbd_open can't start
coroutine/coroutines to read/write some negotiation data?
Paolo
nbd/common.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/nbd/common.c b/nbd/common.c
index dccbb8e9de..4db45b3ede 100644
--- a/nbd/common.c
+++ b/nbd/common.c
@@ -20,6 +20,10 @@
#include "qapi/error.h"
#include "nbd-internal.h"
+/* nbd_wr_syncv
+ * The function may be called from coroutine or from non-coroutine context.
+ * When called from non-coroutine context @ioc must be in blocking mode.
+ */
ssize_t nbd_wr_syncv(QIOChannel *ioc,
struct iovec *iov,
size_t niov,
@@ -42,11 +46,8 @@ ssize_t nbd_wr_syncv(QIOChannel *ioc,
len = qio_channel_writev(ioc, local_iov, nlocal_iov, &local_err);
}
if (len == QIO_CHANNEL_ERR_BLOCK) {
- if (qemu_in_coroutine()) {
- qio_channel_yield(ioc, do_read ? G_IO_IN : G_IO_OUT);
- } else {
- return -EAGAIN;
- }
+ assert(qemu_in_coroutine());
+ qio_channel_yield(ioc, do_read ? G_IO_IN : G_IO_OUT);
continue;
}
if (len < 0) {
--
Best regards,
Vladimir
