Re: [Xen-devel] [livepatch: independ. modules 3/3] python: Add XC binding for Xen build ID

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Thu, Aug 15, 2019 at 09:44:00AM +0000, Pawel Wieczorkiewicz wrote:
> Extend the list of xc() object methods with additional one to display
> Xen's buildid. The implementation follows the libxl implementation
> (e.g. max buildid size assumption being XC_PAGE_SIZE).
> 
> Signed-off-by: Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>
> Reviewed-by: Martin Mazein <amazein@xxxxxxxxx>
> Reviewed-by: Andra-Irina Paraschiv <andraprs@xxxxxxxxxx>
> Reviewed-by: Norbert Manthey <nmanthey@xxxxxxxxx>
> ---
> v2:
> * No code change
> * Adding maintainers
> ---
>  tools/python/xen/lowlevel/xc/xc.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/tools/python/xen/lowlevel/xc/xc.c 
> b/tools/python/xen/lowlevel/xc/xc.c
> index 522cbe3b9c..5459d6834d 100644
> --- a/tools/python/xen/lowlevel/xc/xc.c
> +++ b/tools/python/xen/lowlevel/xc/xc.c
> @@ -1211,6 +1211,26 @@ out:
>      return ret_obj ? ret_obj : pyxc_error_to_exception(self->xc_handle);
>  }
>  
> +static PyObject *pyxc_xenbuildid(XcObject *self)
> +{
> +    xen_build_id_t *buildid;
> +    int i, r;
> +    char *str;
> +
> +    buildid = alloca(sizeof(buildid->len) + XC_PAGE_SIZE);
> +    buildid->len = XC_PAGE_SIZE - sizeof(*buildid);

Those doesn't match. You allocated XC_PAGE_SIZE in addition to
sizeof(buildid->len). I'd change to alloca(XC_PAGE_SIZE) - it is
unlikely that izeof(buildid->len) would be larger than XC_PAGE_SIZE and
we do assume it in other places anyway.

> +
> +    r = xc_version(self->xc_handle, XENVER_build_id, buildid);
> +    if ( r <= 0 )
> +        return pyxc_error_to_exception(self->xc_handle);
> +
> +    str = alloca((r * 2) + 1);
> +    for ( i = 0; i < r; i++ )
> +        snprintf(&str[i * 2], 3, "%02hhx", buildid->buf[i]);
> +
> +    return Py_BuildValue("s", str);
> +}
> +
>  static PyObject *pyxc_xeninfo(XcObject *self)
>  {
>      xen_extraversion_t xen_extra;
> @@ -2294,6 +2314,13 @@ static PyMethodDef pyxc_methods[] = {
>        "Returns [dict]: information about Xen"
>        "        [None]: on failure.\n" },
>  
> +    { "buildid",
> +      (PyCFunction)pyxc_xenbuildid,
> +      METH_NOARGS, "\n"
> +      "Get Xen buildid\n"
> +      "Returns [str]: Xen buildid"
> +      "        [None]: on failure.\n" },
> +
>      { "shadow_control", 
>        (PyCFunction)pyxc_shadow_control, 
>        METH_VARARGS | METH_KEYWORDS, "\n"

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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