perf tools: Enable reading of perf.data files from different ABI rev

This patch allows perf to process perf.data files generated
using an ABI that has a different perf_event_attr struct size,
i.e., a different ABI version.

The perf_event_attr can be extended, yet perf needs to cope with
older perf.data files. Similarly, perf must be able to cope with
a perf.data file which is using a newer version of the ABI than
what it knows about.

This patch adds read_attr(), a routine that reads a
perf_event_attr struct from a file incrementally based on its
advertised size. If the on-file struct is smaller than what perf
knows, then the extra fields are zeroed. If the on-file struct
is bigger, then perf only uses what it knows about, the rest is
skipped.

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: peterz@infradead.org
Cc: acme@redhat.com
Cc: robert.richter@amd.com
Cc: ming.m.lin@intel.com
Cc: andi@firstfloor.org
Cc: asharma@fb.com
Cc: ravitillo@lbl.gov
Cc: vweaver1@eecs.utk.edu
Cc: khandual@linux.vnet.ibm.com
Cc: dsahern@gmail.com
Link: http://lkml.kernel.org/r/1328826068-11713-17-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 2 deletions

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index bec8a328b1b8..e650de8f4396 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -24,7 +24,7 @@ static int perf_session__open(struct perf_session *self, bool force)
 		self->fd = STDIN_FILENO;
 
 		if (perf_session__read_header(self, self->fd) < 0)
-			pr_err("incompatible file format");
+			pr_err("incompatible file format (rerun with -v to learn more)");
 
 		return 0;
 	}
@@ -56,7 +56,7 @@ static int perf_session__open(struct perf_session *self, bool force)
 	}
 
 	if (perf_session__read_header(self, self->fd) < 0) {
-		pr_err("incompatible file format");
+		pr_err("incompatible file format (rerun with -v to learn more)");
 		goto out_close;
 	}