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qemu/io/channel-watch.c
Bin Meng 23f77f05f2 io/channel-watch: Fix socket watch on Windows 
Random failure was observed when running qtests on Windows due to
"Broken pipe" detected by qmp_fd_receive(). What happened is that
the qtest executable sends testing data over a socket to the QEMU
under test but no response is received. The errno of the recv()
call from the qtest executable indicates ETIMEOUT, due to the qmp
chardev's tcp_chr_read() is never called to receive testing data
hence no response is sent to the other side.

tcp_chr_read() is registered as the callback of the socket watch
GSource. The reason of the callback not being called by glib, is
that the source check fails to indicate the source is ready. There
are two socket watch sources created to monitor the same socket
event object from the char-socket backend in update_ioc_handlers().
During the source check phase, qio_channel_socket_source_check()
calls WSAEnumNetworkEvents() to discover occurrences of network
events for the indicated socket, clear internal network event records,
and reset the event object. Testing shows that if we don't reset the
event object by not passing the event handle to WSAEnumNetworkEvents()
the symptom goes away and qtest runs very stably.

It seems we don't need to call WSAEnumNetworkEvents() at all, as we
don't parse the result of WSANETWORKEVENTS returned from this API.
We use select() to poll the socket status. Fix this instability by
dropping the WSAEnumNetworkEvents() call.

Some side notes:

During the testing, I removed the following codes in update_ioc_handlers():

  remove_hup_source(s);
  s->hup_source = qio_channel_create_watch(s->ioc, G_IO_HUP);
  g_source_set_callback(s->hup_source, (GSourceFunc)tcp_chr_hup,
                        chr, NULL);
  g_source_attach(s->hup_source, chr->gcontext);

and such change also makes the symptom go away.

And if I moved the above codes to the beginning, before the call to
io_add_watch_poll(), the symptom also goes away.

It seems two sources watching on the same socket event object is
the key that leads to the instability. The order of adding a source
watch seems to also play a role but I can't explain why.
Hopefully a Windows and glib expert could explain this behavior.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
2022-10-26 13:32:08 +01:00

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/*
* QEMU I/O channels watch helper APIs
*
* Copyright (c) 2015 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/
#include "qemu/osdep.h"
#include "io/channel-watch.h"
typedef struct QIOChannelFDSource QIOChannelFDSource;
struct QIOChannelFDSource {
GSource parent;
GPollFD fd;
QIOChannel *ioc;
GIOCondition condition;
};
#ifdef CONFIG_WIN32
typedef struct QIOChannelSocketSource QIOChannelSocketSource;
struct QIOChannelSocketSource {
GSource parent;
GPollFD fd;
QIOChannel *ioc;
SOCKET socket;
int revents;
GIOCondition condition;
};
#endif
typedef struct QIOChannelFDPairSource QIOChannelFDPairSource;
struct QIOChannelFDPairSource {
GSource parent;
GPollFD fdread;
GPollFD fdwrite;
QIOChannel *ioc;
GIOCondition condition;
};
static gboolean
qio_channel_fd_source_prepare(GSource *source G_GNUC_UNUSED,
gint *timeout)
{
*timeout = -1;
return FALSE;
}
static gboolean
qio_channel_fd_source_check(GSource *source)
{
QIOChannelFDSource *ssource = (QIOChannelFDSource *)source;
return ssource->fd.revents & ssource->condition;
}
static gboolean
qio_channel_fd_source_dispatch(GSource *source,
GSourceFunc callback,
gpointer user_data)
{
QIOChannelFunc func = (QIOChannelFunc)callback;
QIOChannelFDSource *ssource = (QIOChannelFDSource *)source;
return (*func)(ssource->ioc,
ssource->fd.revents & ssource->condition,
user_data);
}
static void
qio_channel_fd_source_finalize(GSource *source)
{
QIOChannelFDSource *ssource = (QIOChannelFDSource *)source;
object_unref(OBJECT(ssource->ioc));
}
#ifdef CONFIG_WIN32
static gboolean
qio_channel_socket_source_prepare(GSource *source G_GNUC_UNUSED,
gint *timeout)
{
*timeout = -1;
return FALSE;
}
/*
* NB, this impl only works when the socket is in non-blocking
* mode on Win32
*/
static gboolean
qio_channel_socket_source_check(GSource *source)
{
static struct timeval tv0;
QIOChannelSocketSource *ssource = (QIOChannelSocketSource *)source;
fd_set rfds, wfds, xfds;
if (!ssource->condition) {
return 0;
}
FD_ZERO(&rfds);
FD_ZERO(&wfds);
FD_ZERO(&xfds);
if (ssource->condition & G_IO_IN) {
FD_SET(ssource->socket, &rfds);
}
if (ssource->condition & G_IO_OUT) {
FD_SET(ssource->socket, &wfds);
}
if (ssource->condition & G_IO_PRI) {
FD_SET(ssource->socket, &xfds);
}
ssource->revents = 0;
if (select(0, &rfds, &wfds, &xfds, &tv0) == 0) {
return 0;
}
if (FD_ISSET(ssource->socket, &rfds)) {
ssource->revents |= G_IO_IN;
}
if (FD_ISSET(ssource->socket, &wfds)) {
ssource->revents |= G_IO_OUT;
}
if (FD_ISSET(ssource->socket, &xfds)) {
ssource->revents |= G_IO_PRI;
}
return ssource->revents;
}
static gboolean
qio_channel_socket_source_dispatch(GSource *source,
GSourceFunc callback,
gpointer user_data)
{
QIOChannelFunc func = (QIOChannelFunc)callback;
QIOChannelSocketSource *ssource = (QIOChannelSocketSource *)source;
return (*func)(ssource->ioc, ssource->revents, user_data);
}
static void
qio_channel_socket_source_finalize(GSource *source)
{
QIOChannelSocketSource *ssource = (QIOChannelSocketSource *)source;
object_unref(OBJECT(ssource->ioc));
}
GSourceFuncs qio_channel_socket_source_funcs = {
qio_channel_socket_source_prepare,
qio_channel_socket_source_check,
qio_channel_socket_source_dispatch,
qio_channel_socket_source_finalize
};
#endif
static gboolean
qio_channel_fd_pair_source_prepare(GSource *source G_GNUC_UNUSED,
gint *timeout)
{
*timeout = -1;
return FALSE;
}
static gboolean
qio_channel_fd_pair_source_check(GSource *source)
{
QIOChannelFDPairSource *ssource = (QIOChannelFDPairSource *)source;
GIOCondition poll_condition = ssource->fdread.revents |
ssource->fdwrite.revents;
return poll_condition & ssource->condition;
}
static gboolean
qio_channel_fd_pair_source_dispatch(GSource *source,
GSourceFunc callback,
gpointer user_data)
{
QIOChannelFunc func = (QIOChannelFunc)callback;
QIOChannelFDPairSource *ssource = (QIOChannelFDPairSource *)source;
GIOCondition poll_condition = ssource->fdread.revents |
ssource->fdwrite.revents;
return (*func)(ssource->ioc,
poll_condition & ssource->condition,
user_data);
}
static void
qio_channel_fd_pair_source_finalize(GSource *source)
{
QIOChannelFDPairSource *ssource = (QIOChannelFDPairSource *)source;
object_unref(OBJECT(ssource->ioc));
}
GSourceFuncs qio_channel_fd_source_funcs = {
qio_channel_fd_source_prepare,
qio_channel_fd_source_check,
qio_channel_fd_source_dispatch,
qio_channel_fd_source_finalize
};
GSourceFuncs qio_channel_fd_pair_source_funcs = {
qio_channel_fd_pair_source_prepare,
qio_channel_fd_pair_source_check,
qio_channel_fd_pair_source_dispatch,
qio_channel_fd_pair_source_finalize
};
GSource *qio_channel_create_fd_watch(QIOChannel *ioc,
int fd,
GIOCondition condition)
{
GSource *source;
QIOChannelFDSource *ssource;
source = g_source_new(&qio_channel_fd_source_funcs,
sizeof(QIOChannelFDSource));
ssource = (QIOChannelFDSource *)source;
ssource->ioc = ioc;
object_ref(OBJECT(ioc));
ssource->condition = condition;
#ifdef CONFIG_WIN32
ssource->fd.fd = (gint64)_get_osfhandle(fd);
#else
ssource->fd.fd = fd;
#endif
ssource->fd.events = condition;
g_source_add_poll(source, &ssource->fd);
return source;
}
#ifdef CONFIG_WIN32
GSource *qio_channel_create_socket_watch(QIOChannel *ioc,
int socket,
GIOCondition condition)
{
GSource *source;
QIOChannelSocketSource *ssource;
WSAEventSelect(socket, ioc->event,
FD_READ | FD_ACCEPT | FD_CLOSE |
FD_CONNECT | FD_WRITE | FD_OOB);
source = g_source_new(&qio_channel_socket_source_funcs,
sizeof(QIOChannelSocketSource));
ssource = (QIOChannelSocketSource *)source;
ssource->ioc = ioc;
object_ref(OBJECT(ioc));
ssource->condition = condition;
ssource->socket = socket;
ssource->revents = 0;
ssource->fd.fd = (gintptr)ioc->event;
ssource->fd.events = G_IO_IN;
g_source_add_poll(source, &ssource->fd);
return source;
}
#else
GSource *qio_channel_create_socket_watch(QIOChannel *ioc,
int socket,
GIOCondition condition)
{
return qio_channel_create_fd_watch(ioc, socket, condition);
}
#endif
GSource *qio_channel_create_fd_pair_watch(QIOChannel *ioc,
int fdread,
int fdwrite,
GIOCondition condition)
{
GSource *source;
QIOChannelFDPairSource *ssource;
source = g_source_new(&qio_channel_fd_pair_source_funcs,
sizeof(QIOChannelFDPairSource));
ssource = (QIOChannelFDPairSource *)source;
ssource->ioc = ioc;
object_ref(OBJECT(ioc));
ssource->condition = condition;
#ifdef CONFIG_WIN32
ssource->fdread.fd = (gint64)_get_osfhandle(fdread);
ssource->fdwrite.fd = (gint64)_get_osfhandle(fdwrite);
#else
ssource->fdread.fd = fdread;
ssource->fdwrite.fd = fdwrite;
#endif
ssource->fdread.events = condition & G_IO_IN;
ssource->fdwrite.events = condition & G_IO_OUT;
g_source_add_poll(source, &ssource->fdread);
g_source_add_poll(source, &ssource->fdwrite);
return source;
}
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