Re: [PATCH] perf tools: Provide backward compatibility with previous perf.data version

Ingo Molnar
2009-10-08T20:32:27Z

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> On Thu, Oct 08, 2009 at 10:12:22PM +0200, Ingo Molnar wrote:
> >
> > * Frederic Weisbecker <fweisbec@gmail.com> wrote:
> >
> > > We have merged the trace.info file into perf.data by adding one
> > > section in the perf headers. This makes it incompatible with previous
> > > version: the new perf tools can't read the older perf.data.
> > >
> > > To support the previous format, we check the headers size. If they
> > > have the same size than in the previous format, then ignore the trace
> > > info section that doesn't exist.
> > >
> > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> > > Cc: Peter Zijlstra <peterz@infradead.org>
> > > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > > Cc: Mike Galbraith <efault@gmx.de>
> > > Cc: Paul Mackerras <paulus@samba.org>
> > > ---
> > > tools/perf/util/header.c | 8 +++++++-
> > > 1 files changed, 7 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> > > index 212fade..9aae360 100644
> > > --- a/tools/perf/util/header.c
> > > +++ b/tools/perf/util/header.c
> > > @@ -287,10 +287,16 @@ struct perf_header *perf_header__read(int fd)
> > > do_read(fd, &f_header, sizeof(f_header));
> > >
> > > if (f_header.magic != PERF_MAGIC ||
> > > - f_header.size != sizeof(f_header) ||
> > > f_header.attr_size != sizeof(f_attr))
> > > die("incompatible file format");
> > >
> > > + if (f_header.size != sizeof(f_header)) {
> > > + /* Support the previous format */
> > > + if (f_header.size == offsetof(typeof(f_header), trace_info))
> > > + f_header.trace_info.size = 0;
> > > + else
> > > + die("incompatible file format");
> > > + }
> > > nr_attrs = f_header.attrs.size / sizeof(f_attr);
> > > lseek(fd, f_header.attrs.offset, SEEK_SET);
> >
> > Perfect - thanks Frederic!
> >
> > This should handle most of the (non-trace) perf.data's out there.
>
>
> Yeah, hopefully. I've only tested in a simple old perf.data but that
> should do the trick for all of the non-trace files.

yeah, i tested it on an old perf.data too, and it worked.

> > trace.info is not something we really want to be backwards compatible
> > about, if we can avoid it.
> >
> > Ingo
>
>
> Yeah, that said, it's still possible and wouldn't require too much
> changes. May be let's wait for complaints and, if any, I can provide
> this backward support too.

ok.

Ingo