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

To: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] libxl: fix against if condition
From: ZhouPeng <zpengxen@xxxxxxxxx>
Date: Sat, 16 Apr 2011 13:48:23 +0800
Cc: "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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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 = "";
> -        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,

>          }
>          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...


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

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