Re: [PATCH] perf record: Delete file if a failure occurs writing the perf data file

[David Ahern <dsahern@gmail.com>]

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On 11/12/13, 8:34 AM, Peter Zijlstra wrote:
> On Tue, Nov 12, 2013 at 08:25:02AM -0700, David Ahern wrote:
>> The patch in this thread deletes the file. Another option is to rewind the
>> file to the last known good write (ie., length after last successful call to
>> write_output).
>
> I'd report a warning and continue with all events that you could read
> upto that point.
>

Coming back to this: the answer to that statement is known. The attached 
patch attempt to rewind to the last good write. Subsequent reads to the 
file fail with:

WARNING: The /tmp/mnt/perf.data file's data size field is 0 which is 
unexpected.
Was the 'perf record' command properly terminated?
reading input file (size expected=3 received=-1)broken or missing trace data
incompatible file format (rerun with -v to learn more)


Given that it would seem deleting the file is the best option.

David

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diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 65615a8bc25e..309f590cf267 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -99,7 +99,22 @@ static int do_write_output(struct perf_record *rec, void *buf, size_t size)
 
 static int write_output(struct perf_record *rec, void *buf, size_t size)
 {
-	return do_write_output(rec, buf, size);
+	off_t len;
+	int rc;
+
+	/* save current length */
+	len = rec->session->header.data_offset + rec->bytes_written;
+
+	rc = do_write_output(rec, buf, size);
+
+	/* on failure reset file to last known good length */
+	if (rc < 0) {
+		pr_debug("truncating file to last known good write: len %ld\n", len);
+	   	if (ftruncate(rec->file.fd, len) != 0)
+			pr_err("Double failure -- write failed and then ftruncate\n");
+	}
+
+	return rc;
 }
 
 static int process_synthesized_event(struct perf_tool *tool,