Re: [PULL 10/11] trace: document how to specify multiple --trace patterns

[Daniel P . Berrangé]

On Mon, Feb 01, 2021 at 06:25:33PM +0100, Paolo Bonzini wrote:
> On 01/02/21 17:54, Kevin Wolf wrote:
> > > How does this option parsing work? Would then multiple patterns separated 
> > > by
> > > comma as in -trace pattern1,pattern2 also work?
> > This would be interpreted as an implied "enable" option with a value of
> > "pattern1,pattern2". I don't think anything splits that string at the
> > comma, so it would look for a trace event matching that string.
> 
> Even worse, it would be interpreted as "-trace enable=pattern1,pattern2=on"
> (and raise a warning since recently).

Maybe we're trying to solve the problem at the wrong level.

The pattern is currently matched using the GLib glob matching APIs.

If we switched to use the GLib regex matching APIs, then we don't need
to repeat the args at all. We could just use regex syntax:

  -trace 'enable=(kvm|virtio)*'

It is a little tedious to have to quote the args to avoid shell
expansion, but as a tradeoff you get much stronger ability todo
complex matches to filter out irrelevant cruft.

If we want to maintain back compat for glob syntax, then we should
support both in parallel and accept a different parameter name
for the regex style.


Regards,
Daniel
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