From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <ian.campbell@citrix.com>
Subject: Re: [PATCH v3 COLOPre 16/26] tools/libx{l,
 c}: add back channel to libxc
Date: Tue, 30 Jun 2015 11:17:09 +0100
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To: Yang Hongyang <yanghy@cn.fujitsu.com>
Cc: wei.liu2@citrix.com, wency@cn.fujitsu.com, andrew.cooper3@citrix.com, yunhong.jiang@intel.com, eddie.dong@intel.com, xen-devel@lists.xen.org, guijianfeng@cn.fujitsu.com, rshriram@cs.ubc.ca, Ian Jackson <Ian.Jackson@eu.citrix.com>
List-Id: xen-devel@lists.xenproject.org

On Thu, 2015-06-25 at 14:25 +0800, Yang Hongyang wrote:

> diff --git a/tools/libxl/libxl_save_callout.c b/tools/libxl/libxl_save_callout.c
> index 12cc57e..25817d6 100644
> --- a/tools/libxl/libxl_save_callout.c
> +++ b/tools/libxl/libxl_save_callout.c
> @@ -27,7 +27,7 @@
>   */
>  static void run_helper(libxl__egc *egc, libxl__save_helper_state *shs,
>                         const char *mode_arg,
> -                       int stream_fd,
> +                       int stream_fd, int back_fd,
>                         const int *preserve_fds, int num_preserve_fds,
>                         const unsigned long *argnums, int num_argnums);
>  
> @@ -70,8 +70,8 @@ void libxl__xc_domain_restore(libxl__egc *egc, libxl__domain_create_state *dcs,
>      dcs->shs.need_results = 1;
>      dcs->shs.toolstack_data_file = 0;
>  
> -    run_helper(egc, &dcs->shs, "--restore-domain", restore_fd, 0,0,
> -               argnums, ARRAY_SIZE(argnums));
> +    run_helper(egc, &dcs->shs, "--restore-domain", restore_fd, dcs->send_fd,

restore_fd comes from convenience aliases, it would be in keeping to do
the same for send_fd too (and elsewhere)

> @@ -174,6 +175,16 @@ static void run_helper(libxl__egc *egc, libxl__save_helper_state *shs,
>          libxl_fd_set_cloexec(CTX, stream_fd, 0);
>          *stream_fd_arg = GCSPRINTF("%d", stream_fd);
>  
> +        if (back_fd <= 2) {
> +            back_fd = dup(back_fd);
> +            if (back_fd < 0) {
> +                LOGE(ERROR,"dup migration back channel");
> +                exit(-1);
> +            }
> +        }
> +        libxl_fd_set_cloexec(CTX, back_fd, 0);
> +        *back_fd_arg = GCSPRINTF("%d", back_fd);

This is an exact duplicate of the stream_fd setup, I think you should
make it a helper which takes a gc, an fd and a const char *what
(=="stream" or "backchannel" for logging) and returns a string
representing a safe (i.e. possibly dupd) version of the fd.

Ian.