Re: [Xen-devel] [PATCH] libxl: fix against if condition

[ZhouPeng <zpengxen@xxxxxxxxx>]

2011/4/15 Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>

ZhouPeng writes ("[Xen-devel] [PATCH] libxl: fix against if condition"):

> Signed-off-by: Zhou Peng <zhoupeng@xxxxxxxxxxxxxxx>
>
> --- a/tools/libxl/libxl_dm.c    Wed Apr 13 14:08:41 2011 +0800
> +++ b/tools/libxl/libxl_dm.c    Wed Apr 13 14:20:37 2011 +0800
> @@ -197,7 +197,7 @@ static char ** libxl_build_device_model_
>          int display = 0;
>          const char *listen = "127.0.0.1";
>
> -        if (info->vncpasswd && info->vncpasswd[0]) {
> +        if (info->vncpasswd && !info->vncpasswd[0]) {
>              assert(!"missing code for supplying vnc password to qemu");

  assert( ) here is missleading, I think.
  In my understanding, assert is offten used to help program debuging,
  telling user the program is runing in exception here and abort it.
  So, I just think "missing code" means "missing passwd code", which tell user must supply an non-empty vnc passwd,
  if vncpasswd is used in vm cfg file.
  It's hard for me to give assert() an relationship with a comment telling something in development, :)
  I think an comment like TODO may be more clear,

  Thanks.

>          }
>          flexarray_append(dm_args, "-vnc");

Looking just at the diff there, I think the original code is correct.
That is, the assert trips when:
 * a password is supplied (info->vncpasswd != NULL)
 * the password is nonemtpy (strlen(info->vncpasswd) > 0
     which is the same as !!info->vncpasswd[0]
 * we're using a new qemu for which this code has not been implemented

That the failure manifests as an assert might be argued to be
unfortunate, but this is still code under development...

Ian.

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-- 
Zhou Peng
Operating System Technology Group
Institute of Software, the Chinese Academy of Sciences (ISCAS)


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