Re: [PATCH 1/2] trace: document how to specify multiple --trace patterns

[Kevin Wolf <kwolf@redhat.com>]

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Am 13.01.2021 um 15:15 hat Stefan Hajnoczi geschrieben:
> On Wed, Jan 13, 2021 at 01:51:17PM +0100, BALATON Zoltan wrote:
> > On Wed, 13 Jan 2021, Stefan Hajnoczi wrote:
> > > On Tue, Jan 12, 2021 at 09:44:03PM +0100, BALATON Zoltan wrote:
> > > > On Tue, 12 Jan 2021, Stefan Hajnoczi wrote:
> > > > > It is possible to repeat the --trace option to specify multiple
> > > > > patterns. This may be preferrable to users who do not want to create a
> > > > > file with a list of patterns.
> > > > > 
> > > > > Suggested-by: BALATON Zoltan <balaton@eik.bme.hu>
> > > > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > ---
> > > > > docs/devel/tracing.rst | 9 +++++++--
> > > > > 1 file changed, 7 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/docs/devel/tracing.rst b/docs/devel/tracing.rst
> > > > > index 4ebf8e38ea..8777c19d14 100644
> > > > > --- a/docs/devel/tracing.rst
> > > > > +++ b/docs/devel/tracing.rst
> > > > > @@ -22,10 +22,15 @@ events::
> > > > > This output comes from the "log" trace backend that is enabled by default when
> > > > > ``./configure --enable-trace-backends=BACKENDS`` was not explicitly specified.
> > > > > 
> > > > > -More than one trace event pattern can be specified by providing a file
> > > > > -instead::
> > > > > +Multiple patterns can be specified by repeating the ``--trace`` option::
> > > > > +
> > > > > +    $ qemu --trace "kvm_*" --trace "virtio_*" ...
> > > > 
> > > > QEMU options are single dash with double dash accepted for compatibility but
> > > > help and other docs have single dash so these (and below) should be -trace.
> > > > (Also a bit less typing for otherwise already way too long command lines.)
> > > 
> > > Is this documented somewhere?
> > 
> > Maybe qemu-system-* -help ?
> 
> I mean developer documentation like CODING_STYLE.rst so we can point to
> that when someone submits a patch that does not use the preferred
> syntax.
> 
> > > I was under the impression that '-' is legacy syntax and '--' is the
> > > preferred syntax. There are examples of '--' on the QEMU man page.
> > 
> > -- is also accepted but they are the same as single dash options. Some tools
> > may have -- syntax preferred but not QEMU itself. If so that may be an
> > inconsistency.
> > 
> > > Let's reach agreement, document it, and then make the documentation
> > > consistent.
> > 
> > Since we don't have long and short arguments for the same options (like
> > -m,--memory) I think -- does not make much sense. Also single dash is less
> > typing and there are other programs using the same convention (e.g. whole X
> > Window System) so I think the current one dash options are fine and should
> > be kept consistent. As long as we can agree on this I can agree with that.
> > :-)
> 
> I'm fine with either (or even using both interchangeably) but want to
> make sure it's agreed for all of QEMU so we can really follow it and
> don't need to spend time on it in the future.
> 
> Kevin: You used '--' in qemu-storage-daemon --help. Does this mean you
> want QEMU to stop using '-'?

qemu-storage-daemon just follows the example of the other tools which
use getopt() instead of a hand-written parser, which means that in all
of the tools, long options require '--'.

I don't have a strong opinion about '-' in the system emulator, though
if I tried out dropping it, I guess I'd find my muscle memory does have
one.

Kevin

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