linux-kernel - [PATCH v4 16/18] perf: enable reading of perf.data files from different ABI rev

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Message-Id: <1327697778-18515-17-git-send-email-eranian@google.com>
Date:	Fri, 27 Jan 2012 21:56:16 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, mingo@...e.hu, acme@...hat.com,
	robert.richter@....com, ming.m.lin@...el.com, andi@...stfloor.org,
	asharma@...com, ravitillo@....gov, vweaver1@...s.utk.edu,
	khandual@...ux.vnet.ibm.com, dsahern@...il.com
Subject: [PATCH v4 16/18] perf: 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a perf.data file which is using a newer version of the ABI than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@...gle.com>
---
 tools/perf/util/header.c |   49 ++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 6f4187d..8d6c18d 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1959,6 +1959,51 @@ static int perf_header__read_pipe(struct perf_session *session, int fd)
 	return 0;
 }
 
+static int read_attr(int fd, struct perf_header *ph,
+		     struct perf_file_attr *f_attr)
+{
+	struct perf_event_attr *attr = &f_attr->attr;
+	size_t sz, left;
+	size_t our_sz = sizeof(f_attr->attr);
+	int ret;
+
+	memset(f_attr, 0, sizeof(*f_attr));
+
+	/* read minimal guaranteed structure */
+	ret = readn(fd, attr, PERF_ATTR_SIZE_VER0);
+	if (ret <= 0)
+		return -1;
+
+	/* on file perf_event_attr size */
+	sz = attr->size;
+	if (ph->needs_swap)
+		sz = bswap_32(sz);
+
+	if (sz == 0) {
+		/* assume ABI0 */
+		sz =  PERF_ATTR_SIZE_VER0;
+	} else if (sz > our_sz) {
+		/* bigger than what we know about */
+		sz = our_sz;
+
+		/* skip what we do not know about */
+		lseek(fd, SEEK_CUR, attr->size - our_sz);
+	}
+	/* what we have not yet read and that we know about */
+	left = sz - PERF_ATTR_SIZE_VER0;
+	if (left) {
+		void *ptr = attr;
+		ptr += PERF_ATTR_SIZE_VER0;
+
+		ret = readn(fd, ptr, left);
+		if (ret <= 0)
+			return -1;
+	}
+	/* read the ids */
+	ret = readn(fd, &f_attr->ids, sizeof(struct perf_file_section));
+	return ret <= 0 ? -1 : 0;
+}
+
 int perf_session__read_header(struct perf_session *session, int fd)
 {
 	struct perf_header *header = &session->header;
@@ -1979,14 +2024,14 @@ int perf_session__read_header(struct perf_session *session, int fd)
 		return -EINVAL;
 	}
 
-	nr_attrs = f_header.attrs.size / sizeof(f_attr);
+	nr_attrs = f_header.attrs.size / f_header.attr_size;
 	lseek(fd, f_header.attrs.offset, SEEK_SET);
 
 	for (i = 0; i < nr_attrs; i++) {
 		struct perf_evsel *evsel;
 		off_t tmp;
 
-		if (readn(fd, &f_attr, sizeof(f_attr)) <= 0)
+		if (read_attr(fd, header, &f_attr) < 0)
 			goto out_errno;
 
 		if (header->needs_swap)
-- 
1.7.1

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