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

Ingo Molnar
2009-10-08T20:13:13Z

* 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.
trace.info is not something we really want to be backwards compatible
about, if we can avoid it.

Ingo