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

[Wen Congyang]

At 12/21/2010 12:05 PM, Wen Congyang Write:
> 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 <address@hidden>
> 
> ---
>  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;
>  }

Ping Again... :)
This is a bug fix.
2 months has gone, but I do not receive any comment.
Should we remove SIGCHLD handling as Paolo said?