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[Qemu-devel] [PULL 02/10] vnc: do not disconnect on EAGAIN
From: |
Gerd Hoffmann |
Subject: |
[Qemu-devel] [PULL 02/10] vnc: do not disconnect on EAGAIN |
Date: |
Thu, 9 Feb 2017 14:01:09 +0100 |
From: Michael Tokarev <address@hidden>
When qemu vnc server is trying to send large update to clients,
there might be a situation when system responds with something
like EAGAIN, indicating that there's no system memory to send
that much data (depending on the network speed, client and server
and what is happening). In this case, something like this happens
on qemu side (from strace):
sendmsg(16, {msg_name(0)=NULL,
msg_iov(1)=[{"\244\"..., 729186}],
msg_controllen=0, msg_flags=0}, 0) = 103950
sendmsg(16, {msg_name(0)=NULL,
msg_iov(1)=[{"lz\346"..., 1559618}],
msg_controllen=0, msg_flags=0}, 0) = -1 EAGAIN
sendmsg(-1, {msg_name(0)=NULL,
msg_iov(1)=[{"lz\346"..., 1559618}],
msg_controllen=0, msg_flags=0}, 0) = -1 EBADF
qemu closes the socket before the retry, and obviously it gets EBADF
when trying to send to -1.
This is because there WAS a special handling for EAGAIN, but now it doesn't
work anymore, after commit 04d2529da27db512dcbd5e99d0e26d333f16efcc, because
now in all error-like cases we initiate vnc disconnect.
This change were introduced in qemu 2.6, and caused numerous grief for many
people, resulting in their vnc clients reporting sporadic random disconnects
from vnc server.
Fix that by doing the disconnect only when necessary, i.e. omitting this
very case of EAGAIN.
Hopefully the existing condition (comparing with QIO_CHANNEL_ERR_BLOCK)
is sufficient, as the original code (before the above commit) were
checking for other errno values too.
Apparently there's another (semi?)bug exist somewhere here, since the
code tries to write to fd# -1, it probably should check if the connection
is open before. But this isn't important.
Signed-off-by: Michael Tokarev <address@hidden>
Reviewed-by: Daniel P. Berrange <address@hidden>
Message-id: address@hidden
Fixes: 04d2529da27db512dcbd5e99d0e26d333f16efcc
Cc: Daniel P. Berrange <address@hidden>
Cc: Gerd Hoffmann <address@hidden>
Cc: address@hidden
Signed-off-by: Gerd Hoffmann <address@hidden>
---
ui/vnc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/ui/vnc.c b/ui/vnc.c
index cdeb79c..f2701e5 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -1256,12 +1256,13 @@ ssize_t vnc_client_io_error(VncState *vs, ssize_t ret,
Error **errp)
if (ret <= 0) {
if (ret == 0) {
VNC_DEBUG("Closing down client sock: EOF\n");
+ vnc_disconnect_start(vs);
} else if (ret != QIO_CHANNEL_ERR_BLOCK) {
VNC_DEBUG("Closing down client sock: ret %zd (%s)\n",
ret, errp ? error_get_pretty(*errp) : "Unknown");
+ vnc_disconnect_start(vs);
}
- vnc_disconnect_start(vs);
if (errp) {
error_free(*errp);
*errp = NULL;
--
1.8.3.1
- [Qemu-devel] [PULL 00/10] vnc: add support for multiple listening sockets., Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 01/10] ui/vnc: Drop unused vnc_has_job() and vnc_jobs_clear(), Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 03/10] ui: fix regression handling bare 'websocket' option to -vnc, Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 07/10] ui: extract code to connect/listen from vnc_display_open, Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 05/10] ui: refactor VncDisplay to allow multiple listening sockets, Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 08/10] ui: let VNC server listen on all resolved IP addresses, Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 09/10] util: add iterators for QemuOpts values, Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 10/10] ui: add ability to specify multiple VNC listen addresses, Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 06/10] ui: refactor code for populating SocketAddress from vnc_display_open, Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 04/10] ui: fix reporting of VNC auth in query-vnc-servers, Gerd Hoffmann, 2017/02/09
- [Qemu-devel] [PULL 02/10] vnc: do not disconnect on EAGAIN,
Gerd Hoffmann <=
- Re: [Qemu-devel] [PULL 00/10] vnc: add support for multiple listening sockets., Peter Maydell, 2017/02/09