lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 6 May 2016 21:40:52 +0800 From: "Wangnan (F)" <wangnan0@...wei.com> To: Arnaldo Carvalho de Melo <acme@...nel.org> CC: <linux-kernel@...r.kernel.org>, Arnaldo Carvalho de Melo <acme@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Zefan Li <lizefan@...wei.com>, <pi3orama@....com> Subject: Re: [PATCH v2 3/4] perf tools: Support reading from backward ring buffer On 2016/5/6 4:07, Arnaldo Carvalho de Melo wrote: > Em Wed, Apr 27, 2016 at 02:19:22AM +0000, Wang Nan escreveu: >> perf_evlist__mmap_read_backward() is introduced for reading backward >> ring buffer. Different from reading forward, before reading, caller >> needs to call perf_evlist__mmap_read_catchup() first. >> >> Backward ring buffer should be read from 'head' pointer, not '0'. >> perf_evlist__mmap_read_catchup() saves 'head' to 'md->prev', then >> make it remember the start position after each reading. >> >> Signed-off-by: Wang Nan <wangnan0@...wei.com> >> Cc: Arnaldo Carvalho de Melo <acme@...hat.com> >> Cc: Peter Zijlstra <peterz@...radead.org> >> Cc: Zefan Li <lizefan@...wei.com> >> Cc: pi3orama@....com >> --- >> tools/perf/util/evlist.c | 39 +++++++++++++++++++++++++++++++++++++++ >> tools/perf/util/evlist.h | 4 ++++ >> 2 files changed, 43 insertions(+) >> >> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c >> index 17cd014..2e0b7b0 100644 >> --- a/tools/perf/util/evlist.c >> +++ b/tools/perf/util/evlist.c >> @@ -766,6 +766,45 @@ union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx) >> return perf_mmap__read(md, evlist->overwrite, old, head, &md->prev); >> } >> >> +union perf_event * >> +perf_evlist__mmap_read_backward(struct perf_evlist *evlist, int idx) >> +{ >> + struct perf_mmap *md = &evlist->mmap[idx]; >> + u64 head, end; >> + u64 start = md->prev; >> + >> + /* >> + * Check if event was unmapped due to a POLLHUP/POLLERR. >> + */ >> + if (!atomic_read(&md->refcnt)) >> + return NULL; >> + >> + /* NOTE: head is negative in this case */ > What is this comment for, can you ellaborate? Are you double sure this > arithmetic with u64, negative values, that -head below are all ok? Yes. In backward ring buffer, kernel write data from '0'. Each time it write a record, it minus sizeof(record) from 'head' pointer. So '-head' means number of bytes already written. > I've applied the first two patches in this series. > > I also need to check why we now need that catchup thing :-\ I think catchup is necessary. I tried to get rid of it by setting md->prev to -1 and initialize it to 0 when reading forwardly and to head when reading backwardly, but it require too much code adjustments. >> + head = perf_mmap__read_head(md); >> + >> + if (!head) >> + return NULL; >> + >> + end = head + md->mask + 1; >> + >> + if ((end - head) > -head) >> + end = 0; >> + This '-head' is used to detect wrapping. Never use positive pointer. >> + return perf_mmap__read(md, false, start, end, &md->prev); >> +} >> + >> +void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx) >> +{ >> + struct perf_mmap *md = &evlist->mmap[idx]; >> + u64 head; >> + >> + if (!atomic_read(&md->refcnt)) >> + return; >> + >> + head = perf_mmap__read_head(md); >> + md->prev = head; >> +} >> + >> static bool perf_mmap__empty(struct perf_mmap *md) >> { >> return perf_mmap__read_head(md) == md->prev && !md->auxtrace_mmap.base; >> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h >> index 208897a..85d1b59 100644 >> --- a/tools/perf/util/evlist.h >> +++ b/tools/perf/util/evlist.h >> @@ -129,6 +129,10 @@ struct perf_sample_id *perf_evlist__id2sid(struct perf_evlist *evlist, u64 id); >> >> union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx); >> >> +union perf_event *perf_evlist__mmap_read_backward(struct perf_evlist *evlist, >> + int idx); >> +void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx); >> + >> void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx); >> >> int perf_evlist__open(struct perf_evlist *evlist); >> -- >> 1.8.3.4
Powered by blists - more mailing lists