linux-kernel - [PATCH v2 1/2] tools subcmd: Add non-waitpid check_if_command

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Message-Id: <20240701044236.475098-2-irogers@google.com>
Date: Sun, 30 Jun 2024 21:42:35 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, James Clark <james.clark@....com>, 
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: [PATCH v2 1/2] tools subcmd: Add non-waitpid check_if_command_finished()

Using waitpid can cause stdout/stderr of the child process to be
lost. Use Linux's /prod/<pid>/status file to determine if the process
has reached the zombie state. Use the 'status' file rather than 'stat'
to avoid issues around skipping the process name.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/lib/subcmd/run-command.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/tools/lib/subcmd/run-command.c b/tools/lib/subcmd/run-command.c
index 4e3a557a2f37..ec06683e77a0 100644
--- a/tools/lib/subcmd/run-command.c
+++ b/tools/lib/subcmd/run-command.c
@@ -2,6 +2,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <ctype.h>
 #include <fcntl.h>
 #include <string.h>
 #include <linux/string.h>
@@ -217,8 +218,40 @@ static int wait_or_whine(struct child_process *cmd, bool block)
 
 int check_if_command_finished(struct child_process *cmd)
 {
+#ifdef __linux__
+	char filename[FILENAME_MAX + 12];
+	char status_line[256];
+	FILE *status_file;
+
+	/*
+	 * Check by reading /proc/<pid>/status as calling waitpid causes
+	 * stdout/stderr to be closed and data lost.
+	 */
+	sprintf(filename, "/proc/%d/status", cmd->pid);
+	status_file = fopen(filename, "r");
+	if (status_file == NULL) {
+		/* Open failed assume finish_command was called. */
+		return true;
+	}
+	while (fgets(status_line, sizeof(status_line), status_file) != NULL) {
+		char *p;
+
+		if (strncmp(status_line, "State:", 6))
+			continue;
+
+		fclose(status_file);
+		p = status_line + 6;
+		while (isspace(*p))
+			p++;
+		return *p == 'Z';
+	}
+	/* Read failed assume finish_command was called. */
+	fclose(status_file);
+	return true;
+#else
 	wait_or_whine(cmd, /*block=*/false);
 	return cmd->finished;
+#endif
 }
 
 int finish_command(struct child_process *cmd)
-- 
2.45.2.803.g4e1b14247a-goog