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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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?

Wei.


> Jan
> 

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