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

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Date:   Tue, 6 Jun 2017 13:04:54 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     David Carrillo-Cisneros <davidcc@...gle.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 Mon, Jun 05, 2017 at 06:32:50PM -0700, David Carrillo-Cisneros wrote:
> 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.

and what if it's bigger than 0xffff?

jirka