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SubjectRe: [PATCH v6 16/18] perf: enable reading of perf.data files from different ABI rev


On 02/09/2012 03:41 PM, Stephane Eranian wrote:
>>> + /* read perf_file_section, ids are read in caller */
>>> + ret = readn(fd, &f_attr->ids, sizeof(f_attr->ids));
>>
>> I thought the above 2 lines were to be removed.
>>
>
> No, They are needed to get the offsets of the ids[] table.
> The field name are confusing. This is not reading the ids[],
> but just the offset of where the table is. Without that you
> get bogus offsets. I ran into that bug during testing...

Hmm.... ok, so the perf_file_attr is now read in back to back reads --
attr then ids -- versus today where it gets both in one readn.

>
>
>> David
>>
>>
>>> +
>>> + return ret <= 0 ? -1 : 0;
>>> +}
>>> +
>>> int perf_session__read_header(struct perf_session *session, int fd)
>>> {
>>> struct perf_header *header = &session->header;
>>> @@ -1974,19 +2019,17 @@ int perf_session__read_header(struct perf_session *session, int fd)
>>> if (session->fd_pipe)
>>> return perf_header__read_pipe(session, fd);
>>>
>>> - if (perf_file_header__read(&f_header, header, fd) < 0) {
>>> - pr_debug("incompatible file format\n");
>>> + if (perf_file_header__read(&f_header, header, fd) < 0)
>>> 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)
>>> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
>>> index 3f3afed..5476320 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;
>>> }
>>>


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