Re: [PATCH v1 4/4] libxl: info: Display build_id of the hypervisor.

[Ian Campbell <ian.campbell@citrix.com>]

On Thu, 2015-10-08 at 22:56 -0400, Konrad Rzeszutek Wilk wrote:
> If the hypervisor is built with we will display it.

I think there is a word missing in this sentence. Perhaps "it" after
"with", or better "a build_id" or "blah blah feature enabled".

> @@ -5295,8 +5298,21 @@ const libxl_version_info*
> libxl_get_version_info(libxl_ctx *ctx)
>      xc_version(ctx->xch, XENVER_commandline, &u.xen_commandline);
>      info->commandline = strdup(u.xen_commandline);
>  
> +    rc = xc_version_len(ctx->xch, XENVER_build_id, &u.build_id, BUILD_ID_LEN);

Please see tools/libxl/CODING_STYLE. A variable called rc must only ever
contain libxl error codes (ERROR_*), which xc_version_len does not return.

"r" or "ret" is appropriate for the return value from a system call or
xc_*.

> +    if (rc > 0) {

Do you intentionally silently ignore a failure here? I think at the very
least you should LOG all but the ones which are expected and which you have
deemed tolerable.

> +        unsigned int i;
> +
> +        info->build_id = (char *)malloc((rc * 2) + 1);

Lack of an error check here, but in any case libxl__zalloc(NOGC, ...)
instead, so it isn't needed anyway.

> +
> +        for (i = 0; i < rc && (i + 1) * 2 < BUILD_ID_LEN; i++)
> +            snprintf(&info->build_id[i * 2], 3, "%02hhx", 
> u.build_id[i]);
> +
> +        info->build_id[i*2]='\0';

You can drop after switching to libxl__zalloc, since the buffer starts out
zeroed.

diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
> index d6ef9a2..232749b 100644
> --- a/tools/libxl/libxl_types.idl
> +++ b/tools/libxl/libxl_types.idl
> @@ -353,6 +353,7 @@ libxl_version_info = Struct("version_info", [
>      ("virt_start",        uint64),
>      ("pagesize",          integer),
>      ("commandline",       string),
> +    ("build_id",          string),

A #define LIBXL_HAVE_* in libxl.h is required to signal the presence of
this new field.