Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755937Ab2BGPuo (ORCPT ); Tue, 7 Feb 2012 10:50:44 -0500 Received: from mail-we0-f174.google.com ([74.125.82.174]:64922 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755585Ab2BGPue convert rfc822-to-8bit (ORCPT ); Tue, 7 Feb 2012 10:50:34 -0500 MIME-Version: 1.0 In-Reply-To: <4F3051E3.5050402@gmail.com> References: <1328187288-24395-1-git-send-email-eranian@google.com> <1328187288-24395-17-git-send-email-eranian@google.com> <4F3051E3.5050402@gmail.com> Date: Tue, 7 Feb 2012 16:50:32 +0100 Message-ID: Subject: Re: [PATCH v5 16/18] perf: enable reading of perf.data files from different ABI rev From: Stephane Eranian To: David Ahern 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 X-System-Of-Record: true Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4997 Lines: 131 On Mon, Feb 6, 2012 at 11:19 PM, David Ahern 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 a perf.data file which is using a newer version of the ABI than 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 >> --- >>  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) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/