[libvirt] [PATCH v2 3/4] log: support logging using shell wildcard syntax

[Daniel P. Berrangé]

On Mon, Apr 30, 2018 at 11:05:48AM -0400, John Ferlan wrote:
> 
> 
> On 04/23/2018 08:28 AM, Daniel P. Berrangé wrote:
> > Rather than specialcasing handling of the '*' character, use fnmatch()
> > to get normal shell wildcard syntax, as described in 'man glob(7)'.
> > 
> > To get an indication of the performance impact of using globs instead
> > of plain string matches, a test program was written. The list of all
> > 260 log categories was extracted from the source. Then a typical log
> > filters setup was picked by creating an array of the strings "qemu",
> > "security", "util", "cgroup", "event", "object". Every filter string
> > was matched against every log category. Timing information showed that
> > using strstr() this took 8 microseconds, while fnmatch() took 114
> > microseconds.
> > 
> > IOW, fnmatch is 14 times slower than our existing strstr check. These
> > numbers show a worst case scenario that wil never be hit, because it
> 
> s/wil/will
> 
> > is rare that every log category would have data output. The log category
> > matches are cached, so each category is only checked once no matter how
> > many log statements are emitted. IOW despite being slower, this will
> > be lost in the noise and have no consequence on real world logging
> > performance.
> > 
> > Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
> > ---
> >  src/util/virlog.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> 
> Reviewed-by: John Ferlan <jferlan at redhat.com>
> 
> John
> 
> BTW: So whether this is available "everywhere" is a bit of an unknown to
> me - as in strstr would seemingly work on every arch, but fnmatch has
> this linux-ism wildcard thing going on which leaves a slight bit of
> doubt in my mind...

NB, we rely on gnulib to provide us fnmatch on all platforms

Regards,
Daniel
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