On Fri, 2014-09-12 at 17:19 +0100, Arnaldo Carvalho de Melo wrote:
> Em Fri, Sep 12, 2014 at 02:58:55PM +0100, Pawel Moll escreveu:
> > On Fri, 2014-09-12 at 14:49 +0100, Arnaldo Carvalho de Melo wrote:
> > > Perhaps both? I.e. an u64 followed from a string, if the u64 is zero,
> > > then there is a string right after it?
>
> > How would this look like in userspace? Something like this?
>
> > 8<----
> > struct perf_event_marker {
> > uint64_t value;
> > char *string;
> > } arg;
>
> > arg.value = 0x1234;
>
> > /* or */
>
> > arg.value = 0;
> > arg.string = "abcd";
>
> > ioctl(fd, PERF_EVENT_IOC_MARKER, &arg)
> > 8<----
>
> > If so, maybe it would simpler just to go for classic size/data
> > structure?
>
> > 8<-----
> > struct perf_event_marker {
> > uint32_t size;
> > void *data;
> > }
> > 8<-----
>
> > This would directly map into struct perf_raw_record...
>
> I can see the usefulness of having it all, i.e. if we do just:
>
> perf trace --pid `pidof some-tool-in-debug-mode-using-this-interface`
Hm. I haven't thought about a situation when 3rd party wants to inject
something into "my" data stream... I guess it could be implemented (a
"pid" member of the struct perf_event_marker with default 0 meaning
"myself"?), but will definitely complicate the patch. Should I have a
look at it now or maybe leave it till we get a general agreement about
the marker ioctl existence?
> Then 'perf trace' doesn't know about any binary format a tool may have,
> getting strings there (hey, LD_PRELOADing some logging library to hook
> into this comes to mind) and having it merged with other events
> (syscalls, pagefaults, etc) looks useful.
But do you still mean a "magic" u64 before the rest? Injecting a string
would just mean:
marker.size = strlen(s) + 1;
marker.data = s;
> As well as some specialized version of 'perf trace' that knows about
> some binary protocol that would get app specific stats or lock status,
> etc, perhaps even plugins for 'perf trace' that would be selected by
> that first u64? Also seems useful.
>
> I.e. having a way to provide just strings and another that would allow
> passing perf_raw_record.
Sounds interesting. But then maybe this stuff shouldn't go into "raw"
then? It could be something like this in the sample:
{ u64 type; /* 0 means zero-terminated string in data */
u32 size;
char data[size]; } && PERF_SAMPLE_MARKER
Pawel
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