Messages in this thread | | | Date | Mon, 12 Oct 2009 11:10:28 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] perf tools: Provide backward compatibility with previous perf.data version |
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> On Thu, Oct 08, 2009 at 10:07:29PM +0200, Frederic Weisbecker 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) || > > > > Few notes about this. > I can send a separate fix for .32 that would just consist in the above line, > or more likely I can replace it by: > > f_header.size < sizeof(f_header) || > > and then we'll get a minimal forward compatibility from the older > tools (can be Cc'ed to stable for .31).
Yep, would be nice.
> Another thing. We may feel the need to add yet another sections in the > future. > > So just a suggestion: we could turn this trace_info section into a > more generic one in which we could add as much subsections as we want > in the future while always ensuring backward compatibility. That could > be managed through a versioning of this generic section.
Definitely! (Since it's not upstream yet we can do it without supporting the interim version.)
Ingo
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