Re: [Xen-devel] per-domain logging

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Oct 10, 2016 at 09:03:49AM +0200, Cedric Bosdonnat wrote:
> On Fri, 2016-10-07 at 15:09 +0100, Wei Liu wrote:
> > Instead of trying to change all the format strings I think it would be
> > better to have a new set of LOG macros that takes domid.
> > 
> > Something like:
> >   LOGEVD(ERROR, errno, domid, "xxxx");
> 
> Sounds good to me, even if LOGEVD will just concatenate something like
> "Domain %d: " to the "xxxx". At least this would be much cleaner in the
> libxl code
> 
> > I would also like to have the log format written down in some document
> > or header file.
> 
> You mean as a documentation? That would be in libxl, not in xtl, right?
> We could have a comment above the LOG*D macros explaining what the message
> will look like (Prepending 'Domain %d: " to the message passed to normal log
> functions). And a comment on top of the current functions explaining all the
> different things that are passed on to xtl.
> 

Presumably you will define LOG*D variants in libxl_internal.h, I think a
comment there right before those macros will be good enough.

> > But let's step back a bit: have we agreed on the approach forward? This
> > thread doesn't seem to have a clear conclusion yet.  Obviously I don't
> > want you to waste your writing code that's going to be threw away.
> 
> I don't want to loose time either, but sometimes it's better to write some
> code to check that what we are mentioning is possible.
> 
> > If you're happy with demuxing in libvirt, I won't object to it. Looks
> > like there is relatively less code churn involved than other solutions,
> > say, libxl keeping track of a set of per-domain xtl loggers.
> 
> Having a set of per-domain xtl logger is also possible, but with one logger
> demuxing all messages, it's fairly easy to support both old log format
> and new ones. And the format we get in the callbacks from libxl is something
> like "%s%s%s%s%s", with things like file, line, function and message. Thus
> adding a domain in there doesn't make much sense. I'ld more in favor of the
> LOG*D family in libxl.
> 

Sure, fine by me.

Wei.

> --
> Cedric

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