Re: [Xen-devel] per-domain logging

[Cedric Bosdonnat <cbosdonnat@xxxxxxxx>]

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.

> 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.

--
Cedric

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