linux-kernel - Re: [PATCH v2 2/5] perf tools: fix piped mode read code

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Date:	Tue, 15 May 2012 20:24:42 -0600
From:	David Ahern <dsahern@...il.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	acme@...hat.com
Subject: Re: [PATCH v2 2/5] perf tools: fix piped mode read code

On 5/15/12 5:28 AM, Stephane Eranian wrote:
> In __perf_session__process_pipe_events(), there was a risk
> we would read more than what a union perf_event struct can
> hold. this could happen in case, perf is reading a file which
> contains new record types it does not know about and which are
> larger than anything it knows about.
>
> In general, perf is supposed to skip records it does not
> understand, but in pipe mode, those have to be read and ignored.
> The fixed size header contains the size of the record, but that
> size may be larger than union perf_event, yet it was used as
> the backing to the read in:
>
>    union perf_event event;
>    void *p;
>
>    size = event->header.size;
>
>    p =&event;
>    p += sizeof(struct perf_event_header);
>    if (size - sizeof(struct perf_event_header)) {
>      err = readn(self->fd, p, size - sizeof(struct perf_event_header));
>
> We fix this by allocating a buffer based on the size reported in
> the header. We reuse the buffer as much as we can. We realloc in
> case it becomes too small. In the  common case, the performance
> impact is negligible.
>
> Signed-off-by: Stephane Eranian<eranian@...gle.com>
> ---
>   tools/perf/util/session.c |   34 ++++++++++++++++++++++++++--------
>   1 files changed, 26 insertions(+), 8 deletions(-)
>

I don't have a file/perf with different sized events, but the change 
makes sense.

Reviewed-and-tested-by: David Ahern <dsahern@...il.com>

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