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

[redcap97]

Public bug reported:

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".

** Affects: qemu
     Importance: Undecided
         Status: New

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

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

Status in QEMU:
  New

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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