From: Stephane Eranian <eranian@google.com>
To: David Ahern <dsahern@gmail.com>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
mingo@elte.hu, acme@redhat.com, robert.richter@amd.com,
ming.m.lin@intel.com, andi@firstfloor.org, asharma@fb.com,
ravitillo@lbl.gov, vweaver1@eecs.utk.edu,
khandual@linux.vnet.ibm.com
Subject: Re: [PATCH v5 16/18] perf: enable reading of perf.data files from different ABI rev
Date: Tue, 7 Feb 2012 16:50:32 +0100 [thread overview]
Message-ID: <CABPqkBSYwwQpfxj3daHF_YHfJWLUT-Pfd03_7_jtrBkO4kM2ag@mail.gmail.com> (raw)
In-Reply-To: <4F3051E3.5050402@gmail.com>
On Mon, Feb 6, 2012 at 11:19 PM, David Ahern <dsahern@gmail.com> wrote:
>
>
> On 02/02/2012 05:54 AM, Stephane Eranian wrote:
>> 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 a perf.data file which is using a newer version of the ABI than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;
>
> As I recall the first bump in that structure happened in 2.6.32. Why add
> backward compatibility for it now? ie., why not just expect VER1
>
>> +
>> + /* 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;
>
> Shouldn't this be a failure? ie., problem with the file (or the
> swapping) since size can't be 0
>
size can be zero. In which case, it means ABI0 version.
See kernel/event/core.c:perf_copy_attr().
> And then for the following why not restrict sz to known, expected sizes
> -- using the PERF_ATTR_SIZE_VER defines introduced in patch 15?
>
Well, the current code solves the problem once and for all. Old tools
can still read new files and vice-versa. If you think that's a problem I
can simply bail out if sz > our_sz.
>> + } 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));
>
> Confused by the above? It is not done in the old code, so why read the
> ids here? I scanned the other patches, but don't see other code movement
> on this file.
>
Good catch. It is leftover code from debugging most likely. The ids are read
later on in perf_session__read_header().
> David
>
>> + 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)
next prev parent reply other threads:[~2012-02-07 15:50 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-02 12:54 [PATCH v5 00/18] perf: add support for sampling taken branches Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 01/18] perf: add generic taken branch sampling support Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 02/18] perf: add Intel LBR MSR definitions Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 03/18] perf: add Intel X86 LBR sharing logic Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 04/18] perf: sync branch stack sampling with X86 precise_sampling Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 05/18] perf: add Intel X86 LBR mappings for PERF_SAMPLE_BRANCH filters Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 06/18] perf: disable LBR support for older Intel Atom processors Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 07/18] perf: implement PERF_SAMPLE_BRANCH for Intel X86 Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 08/18] perf: add LBR software filter support " Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 09/18] perf: disable PERF_SAMPLE_BRANCH_* when not supported Stephane Eranian
2012-02-06 19:23 ` Peter Zijlstra
2012-02-06 19:59 ` Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 10/18] perf: add hook to flush branch_stack on context switch Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 11/18] perf: add code to support PERF_SAMPLE_BRANCH_STACK Stephane Eranian
2012-02-06 18:06 ` Arnaldo Carvalho de Melo
2012-02-07 14:11 ` Stephane Eranian
2012-02-07 15:21 ` Arnaldo Carvalho de Melo
2012-02-02 12:54 ` [PATCH v5 12/18] perf: add support for sampling taken branch to perf record Stephane Eranian
2012-02-06 18:08 ` Arnaldo Carvalho de Melo
2012-02-02 12:54 ` [PATCH v5 13/18] perf: add support for taken branch sampling to perf report Stephane Eranian
2012-02-06 18:14 ` Arnaldo Carvalho de Melo
2012-02-02 12:54 ` [PATCH v5 14/18] perf: fix endianness detection in perf.data Stephane Eranian
2012-02-06 18:17 ` Arnaldo Carvalho de Melo
2012-02-06 18:18 ` Stephane Eranian
2012-02-06 21:47 ` David Ahern
2012-02-06 22:06 ` Arnaldo Carvalho de Melo
2012-02-06 22:29 ` David Ahern
2012-02-07 14:13 ` Stephane Eranian
2012-02-07 14:38 ` Arnaldo Carvalho de Melo
2012-02-17 9:42 ` [tip:perf/core] perf tools: " tip-bot for Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 15/18] perf: add ABI reference sizes Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 16/18] perf: enable reading of perf.data files from different ABI rev Stephane Eranian
2012-02-06 18:19 ` Arnaldo Carvalho de Melo
2012-02-06 18:22 ` Arnaldo Carvalho de Melo
2012-02-07 7:03 ` Anshuman Khandual
2012-02-07 14:52 ` Arnaldo Carvalho de Melo
2012-02-06 22:19 ` David Ahern
2012-02-07 15:50 ` Stephane Eranian [this message]
2012-02-07 16:41 ` David Ahern
2012-02-07 17:42 ` Stephane Eranian
2012-02-07 17:57 ` David Ahern
2012-02-02 12:54 ` [PATCH v5 17/18] perf: fix bug print_event_desc() Stephane Eranian
2012-02-02 12:54 ` [PATCH v5 18/18] perf: make perf able to read file from older ABIs Stephane Eranian
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