[Qemu-devel] Missing system calls retries in case of EINTR

[Yigael Fleishman]

Running qemu on a Ubuntu Feisty host I've encountered an occasional failure-to-launch problem. 
I've used the "-serial /dev/ttyS0" at the command line, and qemu would often exit printing "could not open serial device".
Looking in the srcs I've noticed that  qemu_chr_open_tty does not retry the 'open' syscall if it fails and errno=EINTR.
I've added a retry for such case and it seems to solve that specific problem (see the following patch).
Furthermore, I've noticed that all open, read and some write calls in vl.c are not retried in such cases. 
It seems to me retries should be implemented in those cases, however I might still be missing something here.

--- /tmp/p4diff/vl.c#1.32670    2007-06-25 17:04:53.000000000 -0700
+++ vl.c        2007-06-25 17:04:29.000000000 -0700
@@ -1786,9 +1786,19 @@
     CharDriverState *chr;
     int fd;
 
-    fd = open(filename, O_RDWR | O_NONBLOCK);
-    if (fd < 0)
-        return NULL;
+    /* The following code wraps the 'open' syscall and retries it in case it is interrupted. */
+    while (1)
+    {
+       fd = open(filename, O_RDWR | O_NONBLOCK );
+
+       if (fd < 0)
+       {
+           if (errno != EINTR)
+               return NULL;
+       }
+       else
+           break;
+    }
     fcntl(fd, F_SETFL, O_NONBLOCK);
     tty_serial_init(fd, 115200, 'N', 8, 1);
     chr = qemu_chr_open_fd(fd, fd);