linux-kernel - Re: [PATCH v2 13/13] perf tools: add feature header record to pipe-mode

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Date:   Mon, 5 Jun 2017 18:32:50 -0700
From:   David Carrillo-Cisneros <davidcc@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Simon Que <sque@...omium.org>,
        Wang Nan <wangnan0@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
        He Kuang <hekuang@...wei.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        David Ahern <dsa@...ulusnetworks.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH v2 13/13] perf tools: add feature header record to pipe-mode

On Thu, May 25, 2017 at 1:10 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> On Tue, May 23, 2017 at 12:48:53AM -0700, David Carrillo-Cisneros wrote:
>
> SNIP
>
>> +int perf_event__synthesize_features(struct perf_tool *tool,
>> +                                 struct perf_session *session,
>> +                                 struct perf_evlist *evlist,
>> +                                 perf_event__handler_t process)
>> +{
>> +     struct perf_header *header = &session->header;
>> +     struct feat_fd fdd;
>> +     struct feature_event *fe;
>> +     size_t sz, sz_hdr;
>> +     int feat, ret;
>> +
>> +     sz_hdr = sizeof(fe->header);
>> +     sz = sizeof(union perf_event);
>> +     /* get a nice alignment */
>> +     sz = PERF_ALIGN(sz, getpagesize());
>> +
>> +     memset(&fdd, 0, sizeof(fdd));
>> +
>> +     fdd.buf = malloc(sz);
>> +     if (!fdd.buf)
>> +             return -ENOMEM;
>> +
>> +     fdd.size = sz - sz_hdr;
>> +
>> +     for_each_set_bit(feat, header->adds_features, HEADER_FEAT_BITS) {
>> +             if (!feat_ops[feat].has_record) {
>> +                     pr_debug("No record header feature for header :%d\n", feat);
>> +                     continue;
>> +             }
>> +
>> +             fdd.offset = sizeof(*fe);
>> +
>> +             ret = feat_ops[feat].write(&fdd, evlist);
>> +             if (ret || fdd.offset <= (ssize_t)sizeof(*fe)) {
>> +                     pr_debug("Error writing feature\n");
>> +                     continue;
>> +             }
>> +
>> +             /* fdd.buf may have changed due to realloc in do_write() */
>
> right, so how's ensured the data never cross the maximum event size (0xffff) ?
>
> I think do_write should have some check on that

do_write reallocates ff->buff when it's not large enough.

>
> jirka