Re: [Qemu-devel] What's the intended use of log.h logging?

[Kevin Wolf <kwolf@redhat.com>]

Am 19.10.2015 um 16:29 hat Markus Armbruster geschrieben:
> Points I'd like to make:
> 
> 1. Logging is not tracing.  Logging logs events interesting for the
> user.  Tracing logs code execution.  It's a debugging aid.  The two
> overlap to a degree, but they're not the same.

It's hard to draw a line here because qemu is a tool for debugging
guests. So yes, we're logging code execution, which you call tracing.
It's still output meant for the user. I've been using -d often enough,
and you can easily check that I'm not a regular TCG developer. My goal
was debugging the guest, not qemu.

(By the way, it's a shame that -d int doesn't work with KVM.)

> 2. The current use of log.h seems closer to tracing than to logging.
> 
> 3. I figure our tracing needs could be served by the tracing subsystem
> with a few improvements.  The few things log.h can do that tracing can't
> yet do should be easy enough to add.  Why have two separate subsystems
> then?

I'm not objecting to this as long as the currently supported logging
doesn't get worse.

One important point for me is that our logging gives me nicely formatted
messages, for example register dumps. I'm trying to imagine this being
printed through our existing tracing functions - the horror. It would be
like using QMP query-* commands instead of HMP info, simply not made for
human readers.

Kevin