linux-kernel - [PATCH 3/4] perf session: Avoid calling lseek(2) for pipe

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Date:   Mon, 30 Jan 2023 18:33:49 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users@...r.kernel.org,
        James Clark <james.clark@....com>,
        Leo Yan <leo.yan@...aro.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: [PATCH 3/4] perf session: Avoid calling lseek(2) for pipe

We should not call lseek(2) for pipes as it won't work.  And we already
in the proper place to read the data for AUXTRACE.  Add the comment like
in the PERF_RECORD_HEADER_TRACING_DATA.

Reviewed-by: James Clark <james.clark@....com>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/util/session.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 7c021c6cedb9..fdfe772f2699 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1699,8 +1699,13 @@ static s64 perf_session__process_user_event(struct perf_session *session,
 	case PERF_RECORD_AUXTRACE_INFO:
 		return tool->auxtrace_info(session, event);
 	case PERF_RECORD_AUXTRACE:
-		/* setup for reading amidst mmap */
-		lseek(fd, file_offset + event->header.size, SEEK_SET);
+		/*
+		 * Setup for reading amidst mmap, but only when we
+		 * are in 'file' mode.  The 'pipe' fd is in proper
+		 * place already.
+		 */
+		if (!perf_data__is_pipe(session->data))
+			lseek(fd, file_offset + event->header.size, SEEK_SET);
 		return tool->auxtrace(session, event);
 	case PERF_RECORD_AUXTRACE_ERROR:
 		perf_session__auxtrace_error_inc(session, event);
-- 
2.39.1.456.gfc5497dd1b-goog