Re: [Xen-devel] [PATCH v2 3/3] xl: new "loglvl" command

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.03.16 at 17:01, <wei.liu2@xxxxxxxxxx> wrote:
> On Mon, Mar 14, 2016 at 09:49:11AM -0600, Jan Beulich wrote:
>> >>> On 14.03.16 at 16:36, <wei.liu2@xxxxxxxxxx> wrote:
>> > On Mon, Mar 14, 2016 at 09:23:35AM -0600, Jan Beulich wrote:
>> >> >>> On 08.03.16 at 17:20, <wei.liu2@xxxxxxxxxx> wrote:
>> >> > On Fri, Mar 04, 2016 at 09:48:16AM -0700, Jan Beulich wrote:
>> >> >> --- a/tools/libxl/xl_cmdimpl.c
>> >> >> +++ b/tools/libxl/xl_cmdimpl.c
>> >> >> @@ -6469,6 +6469,84 @@ int main_debug_keys(int argc, char **arg
>> >> >>      return 0;
>> >> >>  }
>> >> >>  
>> >> >> +static const struct {
>> >> >> +    int level;
>> >> >> +    char string[8];
>> >> >> +} loglvls[] = {
>> >> >> +    { 0, "none" },
>> >> >> +    { 1, "error" },
>> >> >> +    { 2, "warning" },
>> >> >> +    { 3, "info" },
>> >> >> +    { 4, "all" },
>> >> >> +    { 4, "debug" },
>> >> > 
>> >> > The semantics of the numbers should go into libxl_types.idl. Maybe
>> >> > something like
>> >> > 
>> >> > # Keep in sync with Xen log level.
>> >> > libxl_xen_log_level = Enumeration (...);
>> >> > 
>> >> > Then in here
>> >> > 
>> >> >     static const struct {
>> >> >         int level;
>> >> >         char string[8];
>> >> >     } loglvls[] = {
>> >> >         { LIBXL_XEN_LOG_LEVEL_NONE, "none" },
>> >> >         { ..., "error" },
>> >> >         { ..., "warning" },
>> >> >         { ..., "info" },
>> >> >         { ..., "all" },
>> >> >         { ..., "debug" },
>> >> > 
>> >> > Please also note that after the introduction of this API, Xen log level
>> >> > will become part of the stable API and subject to some compatibility
>> >> > constraints. Is this what you wanted?
>> >> 
>> >> No, and I actually I'm having trouble following your request: This
>> >> lives in xl_cmdimpl.c, which I didn't think is subject to any stability
>> >> requirements in the mapping of strings (from the xl command line)
>> >> to numbers. It is _specifically_ that I do not want to fix those
>> >> mappings.
>> > 
>> > The new API libxl_log_level relies on the semantics of these mappings.
>> > To make the new API useful to all clients, the semantics of log levels
>> > needs to go into libxl_types.idl (as mentioned a few lines above), hence
>> > it becomes part of the stable API. Otherwise you end up with an API
>> > accepting arbitrary magic numbers.
>> 
>> Well - what do you suggest? I'm meanwhile willing to give up on this,
>> as baking the mapping into some ABI is clearly not what we should do
>> or what I want. Moving the translation into libxl also wouldn't help.
>> Which would leave the option of doing this in libxc, but then again I'm
>> generally opposed to passing around strings instead of numbers, as
>> the latter are better to work with at all layers.
>> 
> 
> I don't have a very clear idea on what to suggest at the moment, sorry.
> What kind of changes to xen log level might happen in the future?

They could become more fine grained (for example, Linux has a
few more than we have now). And the string/number correlation
is an implementation detail anyway.

Jan


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