linux-kernel - [PATCH] perf tools: Add --debug-file option to redirect debug output

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Date:   Tue, 31 Oct 2023 10:55:23 +0000
From:   Yang Jihong <yangjihong1@...wei.com>
To:     <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
        <jolsa@...nel.org>, <namhyung@...nel.org>, <irogers@...gle.com>,
        <adrian.hunter@...el.com>, <linux-perf-users@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <yangjihong1@...wei.com>
Subject: [PATCH] perf tools: Add --debug-file option to redirect debug output

Currently, debug messages is output to stderr, add --debug-file option to
support redirection to a specified file.

Some test scenarios:

  # perf --list-opts
  --help --version --exec-path --html-path --paginate --no-pager --debugfs-dir --buildid-dir --list-cmds --list-opts --debug --debug-file

  # perf --debug-file
  No path given for --debug-file.

   Usage: perf [--version] [--help] [OPTIONS] COMMAND [ARGS]

  # perf --debug-file /sys/perf.log record -v true
  Open debug file '/sys/perf.log' failed: Permission denied

   Usage: perf [--version] [--help] [OPTIONS] COMMAND [ARGS]

  # perf --debug-file /tmp/perf.log record -v true
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.013 MB perf.data (26 samples) ]
  # cat /tmp/perf.log
  DEBUGINFOD_URLS=
  Using CPUID GenuineIntel-6-3E-4
  nr_cblocks: 0
  affinity: SYS
  mmap flush: 1
  comp level: 0
  mmap size 528384B
  Control descriptor is not initialized
  mmap size 528384B
  Looking at the vmlinux_path (8 entries long)
  Using /proc/kcore for kernel data
  Using /proc/kallsyms for symbols
  symbol:unmap_start file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:unmap_complete file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:map_start file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:map_complete file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:reloc_start file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:reloc_complete file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:init_start file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:init_complete file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:lll_lock_wait_private file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:lll_lock_wait file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:setjmp file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:longjmp file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:longjmp_target file:(null) line:0 offset:0 return:0 lazy:(null)
  failed to write feature HYBRID_TOPOLOGY

Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
---
 tools/perf/Documentation/perf.txt |  3 +++
 tools/perf/perf.c                 | 30 ++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/tools/perf/Documentation/perf.txt b/tools/perf/Documentation/perf.txt
index ba3df49c169d..a7cf7bc2f968 100644
--- a/tools/perf/Documentation/perf.txt
+++ b/tools/perf/Documentation/perf.txt
@@ -64,6 +64,9 @@ OPTIONS
           perf-event-open  - Print perf_event_open() arguments and
                              return value
 
+--debug-file::
+	Write debug output to a specified file.
+
 DESCRIPTION
 -----------
 Performance counters for Linux are a new kernel-based subsystem
diff --git a/tools/perf/perf.c b/tools/perf/perf.c
index d3fc8090413c..921bee0a6437 100644
--- a/tools/perf/perf.c
+++ b/tools/perf/perf.c
@@ -39,6 +39,7 @@
 #include <linux/zalloc.h>
 
 static int use_pager = -1;
+static FILE *debug_fp = NULL;
 
 struct cmd_struct {
 	const char *cmd;
@@ -162,6 +163,19 @@ static void commit_pager_choice(void)
 	}
 }
 
+static int set_debug_file(const char *path)
+{
+	debug_fp = fopen(path, "w");
+	if (!debug_fp) {
+		fprintf(stderr, "Open debug file '%s' failed: %s\n",
+			path, strerror(errno));
+		return -1;
+	}
+
+	debug_set_file(debug_fp);
+	return 0;
+}
+
 struct option options[] = {
 	OPT_ARGUMENT("help", "help"),
 	OPT_ARGUMENT("version", "version"),
@@ -174,6 +188,7 @@ struct option options[] = {
 	OPT_ARGUMENT("list-cmds", "list-cmds"),
 	OPT_ARGUMENT("list-opts", "list-opts"),
 	OPT_ARGUMENT("debug", "debug"),
+	OPT_ARGUMENT("debug-file", "debug-file"),
 	OPT_END()
 };
 
@@ -287,6 +302,18 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 
 			(*argv)++;
 			(*argc)--;
+		} else if (!strcmp(cmd, "--debug-file")) {
+			if (*argc < 2) {
+				fprintf(stderr, "No path given for --debug-file.\n");
+				usage(perf_usage_string);
+			}
+
+			if (set_debug_file((*argv)[1]))
+				usage(perf_usage_string);
+
+			(*argv)++;
+			(*argc)--;
+
 		} else {
 			fprintf(stderr, "Unknown option: %s\n", cmd);
 			usage(perf_usage_string);
@@ -547,5 +574,8 @@ int main(int argc, const char **argv)
 	fprintf(stderr, "Failed to run command '%s': %s\n",
 		cmd, str_error_r(errno, sbuf, sizeof(sbuf)));
 out:
+	if (debug_fp)
+		fclose(debug_fp);
+
 	return 1;
 }
-- 
2.34.1