[Qemu-devel] [Bug 1586756] Re: "-serial unix:" option of qemu-system-arm is broken in qemu 2.6.0

[Daniel Berrange]

Ok, now it makes more sense. You are using the socket chardev in TCP
outgoing client mode, which used to be blocking by default. In 2.6 this
switched to match TCP server mode,  in wich the incoming client was
always in non-blocking mode.

IOW, this arm code was already broken in 2.5 just depending on which
chardev config was used.

So, we'll need to put a fix in pl011_write.  I'm unsure whether use
writeall() is the correct behaviour - I'll come to other serial
backends.

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https://bugs.launchpad.net/bugs/1586756

Title:
  "-serial unix:" option of qemu-system-arm is broken in qemu 2.6.0

Status in QEMU:
  Incomplete

Bug description:
  I found a bug of "-serial unix:PATH_TO_SOCKET" in qemu 2.6.0 (qemu 2.5.1 
works fine).
  Occasionally, a part of the output of qemu disappears in the bug.

  It looks like following commit is the cause:

  char: ensure all clients are in non-blocking mode (Author: Daniel P. Berrange 
<address@hidden>)
  
http://git.qemu.org/?p=qemu.git;a=commitdiff;h=64c800f808748522727847b9cdc73412f22dffb9

  In this commit, UNIX socket is set to non-blocking mode, but 
qemu_chr_fe_write function doesn't handle EAGAIN.
  You should fix code like that:

  ---
  diff --git a/qemu-char.c b/qemu-char.c
  index b597ee1..0361d78 100644
  --- a/qemu-char.c
  +++ b/qemu-char.c
  @@ -270,6 +270,7 @@ static int qemu_chr_fe_write_buffer(CharDriverState *s, 
const uint8_t *buf, int
   int qemu_chr_fe_write(CharDriverState *s, const uint8_t *buf, int len)
   {
       int ret;
  +    int offset = 0;
   
       if (s->replay && replay_mode == REPLAY_MODE_PLAY) {
           int offset;
  @@ -280,7 +281,21 @@ int qemu_chr_fe_write(CharDriverState *s, const uint8_t 
*buf, int len)
       }
   
       qemu_mutex_lock(&s->chr_write_lock);
  -    ret = s->chr_write(s, buf, len);
  +
  +    while (offset < len) {
  +    retry:
  +        ret = s->chr_write(s, buf, len);
  +        if (ret < 0 && errno == EAGAIN) {
  +            g_usleep(100);
  +            goto retry;
  +        }
  +
  +        if (ret <= 0) {
  +            break;
  +        }
  +
  +        offset += ret;
  +    }
   
       if (ret > 0) {
           qemu_chr_fe_write_log(s, buf, ret);
  ---

  Or please do "git revert 64c800f808748522727847b9cdc73412f22dffb9".

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