linux-kernel - Re: [PATCH] perf data: if a bad header size, retry in pipe mode

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Message-ID: <20200414125105.GC117177@krava>
Date:   Tue, 14 Apr 2020 14:51:05 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf data: if a bad header size, retry in pipe mode

On Thu, Apr 09, 2020 at 11:57:44AM -0700, Ian Rogers wrote:
> Currently pipe mode files fail like:
> $ perf record -o - sleep 1 > /tmp/perf.pipe.data
> $ perf report -i /tmp/perf.pipe.data
> incompatible file format (rerun with -v to learn more)
> 
> This change makes it so that if a perf.data file's header size is wrong
> it is re-checked in pipe mode, where if wrong it fails as it currently
> does.
> 

hi,
how about doing it the other way round like below,
read header and find out if it's pipe..

seems it's less changes

jirka


---
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index acbd046bf95c..20c34cec9a46 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -3469,7 +3469,7 @@ static int perf_header__read_pipe(struct perf_session *session)
 		return -EINVAL;
 	}
 
-	return 0;
+	return f_header.size == sizeof(f_header) ? 0 : -1;
 }
 
 static int read_attr(int fd, struct perf_header *ph,
@@ -3571,7 +3571,7 @@ int perf_session__read_header(struct perf_session *session)
 	struct perf_file_header	f_header;
 	struct perf_file_attr	f_attr;
 	u64			f_id;
-	int nr_attrs, nr_ids, i, j;
+	int nr_attrs, nr_ids, i, j, err;
 	int fd = perf_data__fd(data);
 
 	session->evlist = evlist__new();
@@ -3580,8 +3580,16 @@ int perf_session__read_header(struct perf_session *session)
 
 	session->evlist->env = &header->env;
 	session->machines.host.env = &header->env;
-	if (perf_data__is_pipe(data))
-		return perf_header__read_pipe(session);
+
+	/*
+	 * We could still read 'pipe' data from regular file,
+	 * check for the pipe header first.
+	 */
+	err = perf_header__read_pipe(session);
+	if (!err || (err && perf_data__is_pipe(data))) {
+		data->is_pipe = true;
+		return err;
+	}
 
 	if (perf_file_header__read(&f_header, header, fd) < 0)
 		return -EINVAL;