qemu-e2k/chardev
Thomas Huth 4f7689f081 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>
2023-10-03 15:40:09 +04:00
..
baum.c replace TABs with spaces 2023-03-20 12:43:50 +01:00
char-console.c
char-fd.c Refactoring: refactor TFR() macro to RETRY_ON_EINTR() 2023-01-09 13:50:47 +01:00
char-fe.c chardev: mark explicitly first argument as poisoned 2021-08-05 16:15:33 +04:00
char-file.c chardev: Allow setting file chardev input file on the command line 2023-04-20 06:50:11 +02:00
char-hmp-cmds.c char: Move HMP commands from monitor/ to chardev/ 2023-02-04 07:56:54 +01:00
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
char-parallel.c chardev: clean up chardev-parallel.c 2023-01-11 10:44:33 +01:00
char-pipe.c Refactoring: refactor TFR() macro to RETRY_ON_EINTR() 2023-01-09 13:50:47 +01:00
char-pty.c chardev/char-pty: Avoid losing bytes when the other side just (re-)connected 2023-10-03 15:40:09 +04:00
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 misc/other: spelling fixes 2023-09-08 13:08:52 +03:00
char-stdio.c chardev: replace qemu_set_nonblock() 2022-05-03 15:51:52 +04:00
char-udp.c qapi chardev: Elide redundant has_FOO in generated C 2022-12-14 20:04:47 +01:00
char-win-stdio.c chardev/char-win-stdio: Support VT sequences on Windows 11 host 2023-06-27 17:08:56 +02:00
char-win.c
char.c misc/other: spelling fixes 2023-09-08 13:08:52 +03:00
chardev-internal.h Clean up decorations and whitespace around header guards 2022-05-11 16:50:32 +02:00
meson.build configure, meson: remove target OS symbols from config-host.mak 2023-09-07 13:32:37 +02:00
msmouse.c chardev: fix segfault in finalize 2022-09-29 14:38:05 +04:00
spice.c ui/spice: Require spice-server >= 0.14.0 2023-01-19 13:30:01 +01:00
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
wctablet.c chardev: fix segfault in finalize 2022-09-29 14:38:05 +04:00