[Qemu-devel] [PATCH v2] disable sigcld handling before calling pclose()

[Wen Congyang]

When I use the command 'virsh save' to save the domain state,
I receive the following error message:
operation failed: Migration unexpectedly failed.

I debug the qemu by adding some printf(), and find the function
pclose() returns -1.

I use strace to trace qemu, the log is as the following:
======
close(17)                               = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
wait4(-1, NULL, WNOHANG, NULL)          = 22016
rt_sigreturn(0)                         = 0
wait4(22016, 0x7fff7f1034fc, 0, NULL)   = -1 ECHILD (No child processes)
======

We wait the child twice: one is in signal SIGCHLD handling and the other
one is in pclose().

We should disable sigcld handling before calling pclose().

v2:
- Add stub functions for Win32

Signed-off-by: Wen Congyang <we...@cn.fujitsu.com>

---
 os-posix.c      |   19 +++++++++++++++++++
 qemu-os-posix.h |    2 ++
 qemu-os-win32.h |    2 ++
 savevm.c        |    2 ++
 4 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/os-posix.c b/os-posix.c
index 38c29d1..b163995 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -86,6 +86,25 @@ void os_setup_signal_handling(void)
     sigaction(SIGCHLD, &act, NULL);
 }
 
+void os_stop_sigchld_handling(void)
+{
+    struct sigaction act;
+
+    memset(&act, 0, sizeof(act));
+    act.sa_handler = SIG_DFL;
+    sigaction(SIGCHLD, &act, NULL);
+}
+
+void os_resume_sigchld_handling(void)
+{
+    struct sigaction act;
+
+    memset(&act, 0, sizeof(act));
+    act.sa_handler = sigchld_handler;
+    act.sa_flags = SA_NOCLDSTOP;
+    sigaction(SIGCHLD, &act, NULL);
+}
+
 /* Find a likely location for support files using the location of the binary.
    For installed binaries this will be "$bindir/../share/qemu".  When
    running from the build tree this will be "$bindir/../pc-bios".  */
diff --git a/qemu-os-posix.h b/qemu-os-posix.h
index 81fd9ab..1c317f1 100644
--- a/qemu-os-posix.h
+++ b/qemu-os-posix.h
@@ -33,6 +33,8 @@ static inline void os_host_main_loop_wait(int *timeout)
 void os_set_line_buffering(void);
 void os_set_proc_name(const char *s);
 void os_setup_signal_handling(void);
+void os_stop_sigchld_handling(void);
+void os_resume_sigchld_handling(void);
 void os_daemonize(void);
 void os_setup_post(void);
 
diff --git a/qemu-os-win32.h b/qemu-os-win32.h
index 1a07e5e..f31c5ef 100644
--- a/qemu-os-win32.h
+++ b/qemu-os-win32.h
@@ -43,6 +43,8 @@ void qemu_del_wait_object(HANDLE handle, WaitObjectFunc 
*func, void *opaque);
 void os_host_main_loop_wait(int *timeout);
 
 static inline void os_setup_signal_handling(void) {}
+static inline void os_stop_sigchld_handling(void) {}
+static inline void os_resume_sigchld_handling(void) {}
 static inline void os_daemonize(void) {}
 static inline void os_setup_post(void) {}
 void os_set_line_buffering(void);
diff --git a/savevm.c b/savevm.c
index 90aa237..387b70b 100644
--- a/savevm.c
+++ b/savevm.c
@@ -234,7 +234,9 @@ static int stdio_pclose(void *opaque)
 {
     QEMUFileStdio *s = opaque;
     int ret;
+    os_stop_sigchld_handling();
     ret = pclose(s->stdio_file);
+    os_resume_sigchld_handling();
     qemu_free(s);
     return ret;
 }
-- 
1.7.1