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Subject[PATCH v4 16/18] perf: enable reading of perf.data files from different ABI rev
Date
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a perf.data file which is using a newer version of the ABI than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>
---
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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