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hw: replace most use of qemu_chr_fe_write with qemu_chr_fe_write_all

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The qemu_chr_fe_write method will return -1 on EAGAIN if the
chardev backend write would block. Almost no callers of the
qemu_chr_fe_write() method check the return value, instead
blindly assuming data was successfully sent. In most cases
this will lead to silent data loss on interactive consoles,
but in some cases (eg RNG EGD) it'll just cause corruption
of the protocol being spoken.

We unfortunately can't fix the virtio-console code, due to
a bug in the Linux guest drivers, which would cause the
entire Linux kernel to hang if we delay processing of the
incoming data in any way. Fixing this requires first fixing
the guest driver to not hold spinlocks while writing to the
hvc device backend.

Fixes bug: https://bugs.launchpad.net/qemu/+bug/1586756

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1473170165-540-4-git-send-email-berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Daniel P. Berrange 2016-09-06 14:56:04 +01:00 • committed by Paolo Bonzini
parent 7983e82933
commit 6ab3fc32ea
29 changed files with 104 additions and 27 deletions
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2
hw/char/lm32_uart.c
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@ -178,6 +178,8 @@ static void uart_write(void *opaque, hwaddr addr,
switch (addr) {
case R_RXTX:
if (s->chr) {
/* XXX this blocks entire thread. Rewrite to use
* qemu_chr_fe_write and background I/O callbacks */
qemu_chr_fe_write_all(s->chr, &ch, 1);
}
break;