Re: [Patch v2 2/3] correct xc_domain_save()'s return value

[Wen Congyang <wency@cn.fujitsu.com>]

On 11/14/2014 10:57 PM, Ian Jackson wrote:
> Wen Congyang writes ("[Patch v2 2/3] correct xc_domain_save()'s return value"):
>> If suspend_and_state() fails, the errno may be 0. But we assume
>> that the errno is not 0. So remove assert().
> 
> Thanks for spotting this.
> 
> I think this is going in the wrong direction.  Perhaps we could
> instead do something like the patch below ?  Please let me know what
> you think.
> 
> If you think this is a better idea, please submit it as a proper patch
> with a proper commit message.

OK, I will do it.

> 
> (Ideally we would fix the actual suspend hook in libxl, to always set
> errno, but that's too invasive a set of changes to do now, I think.)

libxl and helper program are two programs, and we should update the interface
between libxl and the hepler program first. We can do it later.

Thanks
Wen Congyang

> 
> Thanks,
> Ian.
> 
> Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
> 
> diff --git a/tools/libxc/include/xenguest.h b/tools/libxc/include/xenguest.h
> index 40bbac8..3ab9dd8 100644
> --- a/tools/libxc/include/xenguest.h
> +++ b/tools/libxc/include/xenguest.h
> @@ -35,7 +35,9 @@
>  /* callbacks provided by xc_domain_save */
>  struct save_callbacks {
>      /* Called after expiration of checkpoint interval,
> -     * to suspend the guest.
> +     * to suspend the guest.  Returns 1 for success, or 0 for failure.
> +     * On failure it should ideally set errno.  (If it leaves errno
> +     * as 0, EIO will be used instead.)
>       */
>      int (*suspend)(void* data);
>  
> diff --git a/tools/libxc/xc_domain_save.c b/tools/libxc/xc_domain_save.c
> index 254fdb3..444aac6 100644
> --- a/tools/libxc/xc_domain_save.c
> +++ b/tools/libxc/xc_domain_save.c
> @@ -361,9 +361,15 @@ static int suspend_and_state(int (*suspend)(void*), void* data,
>                               xc_interface *xch, int io_fd, int dom,
>                               xc_dominfo_t *info)
>  {
> +    errno = 0;
>      if ( !(*suspend)(data) )
>      {
> -        ERROR("Suspend request failed");
> +        if (!errno) {
> +            errno = EIO;
> +            ERROR("Suspend request failed (without errno, using EINVAL)");
> +        } else {
> +            ERROR("Suspend request failed");
> +        }
>          return -1;
>      }
>  
> .
>