mirror_qemu/chardev
Thomas Huth 5f2b5606e2 chardev/char-pty: Avoid losing bytes when the other side just (re-)connected
When starting a guest via libvirt with "virsh start --console ...",
the first second of the console output is missing. This is especially
annoying on s390x that only has a text console by default and no graphical
output - if the bios fails to boot here, the information about what went
wrong is completely lost.

One part of the problem (there is also some things to be done on the
libvirt side) is that QEMU only checks with a 1 second timer whether
the other side of the pty is already connected, so the first second of
the console output is always lost.

This likely used to work better in the past, since the code once checked
for a re-connection during write, but this has been removed in commit
f8278c7d74 ("char-pty: remove the check for connection on write") to avoid
some locking.

To ease the situation here at least a little bit, let's check with g_poll()
whether we could send out the data anyway, even if the connection has not
been marked as "connected" yet. The file descriptor is marked as non-blocking
anyway since commit fac6688a18 ("Do not hang on full PTY"), so this should
not cause any trouble if the other side is not ready for receiving yet.

With this patch applied, I can now successfully see the bios output of
a s390x guest when running it with "virsh start --console" (with a patched
version of virsh that fixes the remaining issues there, too).

Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230816210743.1319018-1-thuth@redhat.com>
(cherry picked from commit 4f7689f081)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: use TFR() instead of RETRY_ON_EINTR() before v7.2.0-538-g8b6aa69365)
2023-10-21 14:04:51 +03:00
..
baum.c chardev/baum: Avoid dynamic stack allocation 2022-09-22 16:38:28 +01:00
char-console.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
char-fd.c chardev: replace qemu_set_nonblock() 2022-05-03 15:51:52 +04:00
char-fe.c chardev: mark explicitly first argument as poisoned 2021-08-05 16:15:33 +04:00
char-file.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
char-io.c QIOChannel: Add flags on io_writev and introduce io_flush callback 2022-05-16 13:56:24 +01:00
char-mux.c chardev: don't exit() straight away on C-a x 2021-11-04 10:32:01 +00:00
char-null.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
char-parallel.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
char-pipe.c Remove qemu-common.h include from most units 2022-04-06 14:31:55 +02:00
char-pty.c chardev/char-pty: Avoid losing bytes when the other side just (re-)connected 2023-10-21 14:04:51 +03:00
char-ringbuf.c Use DECLARE_*CHECKER* macros 2020-09-09 09:27:09 -04:00
char-serial.c chardev: replace qemu_set_nonblock() 2022-05-03 15:51:52 +04:00
char-socket.c chardev/char-socket: set s->listener = NULL in char_socket_finalize 2023-03-29 10:20:04 +03:00
char-stdio.c chardev: replace qemu_set_nonblock() 2022-05-03 15:51:52 +04:00
char-udp.c qapi: Convert simple union SocketAddressLegacy to flat one 2021-09-27 08:23:25 +02:00
char-win-stdio.c chardev/char-win-stdio: Pass Ctrl+C to guest with a multiplexed monitor 2022-11-21 11:30:11 +04:00
char-win.c chardev: Improve error report by calling error_setg_win32() 2020-03-09 13:36:15 +01:00
char.c chardev: src buffer const for write functions 2022-09-29 14:38:05 +04:00
chardev-internal.h Clean up decorations and whitespace around header guards 2022-05-11 16:50:32 +02:00
meson.build char: move qemu_openpty_raw from util/ to char/ 2022-04-06 10:50:37 +02:00
msmouse.c chardev: fix segfault in finalize 2022-09-29 14:38:05 +04:00
spice.c chardev-spice: add missing module_obj directive 2021-07-22 14:44:47 +02:00
testdev.c Use DECLARE_*CHECKER* macros 2020-09-09 09:27:09 -04:00
trace-events docs: fix references to docs/devel/tracing.rst 2021-06-02 06:51:09 +02:00
trace.h trace: switch position of headers to what Meson requires 2020-08-21 06:18:24 -04:00
wctablet.c chardev: fix segfault in finalize 2022-09-29 14:38:05 +04:00