From: Karel Zak <kzak@redhat.com>
Date: Thu, 11 Aug 2022 10:56:02 +0200
Subject: [PATCH 06/24] lib/procfs: add function to parse /proc/#/stat

Signed-off-by: Karel Zak <kzak@redhat.com>
---
 include/procfs.h |  1 +
 lib/procfs.c     | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/include/procfs.h b/include/procfs.h
index 5a730c9..825689b 100644
--- a/include/procfs.h
+++ b/include/procfs.h
@@ -30,6 +30,7 @@ extern ssize_t procfs_process_get_cmdline(struct path_cxt *pc, char *buf, size_t
 extern ssize_t procfs_process_get_cmdname(struct path_cxt *pc, char *buf, size_t bufsz);
 extern ssize_t procfs_process_get_stat(struct path_cxt *pc, char *buf, size_t bufsz);
 
+extern int procfs_process_get_stat_nth(struct path_cxt *pc, int n, uintmax_t *re);
 
 static inline ssize_t procfs_process_get_exe(struct path_cxt *pc, char *buf, size_t bufsz)
 {
diff --git a/lib/procfs.c b/lib/procfs.c
index 4d6d25b..16a8c04 100644
--- a/lib/procfs.c
+++ b/lib/procfs.c
@@ -166,6 +166,35 @@ ssize_t procfs_process_get_stat(struct path_cxt *pc, char *buf, size_t bufsz)
 	return procfs_process_get_line_for(pc, buf, bufsz, "stat");
 }
 
+int procfs_process_get_stat_nth(struct path_cxt *pc, int n, uintmax_t *re)
+{
+	ssize_t rc;
+	char *key = NULL, *tok, *p;
+	char buf[BUFSIZ];
+	int i;
+
+	if (n == 2 || n == 3)		/* process name and status (strings) */
+		return -EINVAL;
+
+	rc = procfs_process_get_line_for(pc, buf, sizeof(buf), "stat");
+	if (rc < 0)
+		return rc;
+
+	for (i = 0, tok = strtok_r(buf, " ", &key); tok;
+	     tok = strtok_r(NULL, " ", &key)) {
+
+		i++;
+		if (i == n)
+			return ul_strtou64(tok, re, 10);
+
+		/* skip rest of the process name */
+		if (i == 2 && (p = strchr(key, ')')))
+			key = p + 2;
+	}
+
+	return -EINVAL;
+}
+
 int procfs_process_get_uid(struct path_cxt *pc, uid_t *uid)
 {
 	struct stat sb;
@@ -536,6 +565,30 @@ static int test_isprocfs(int argc, char *argv[])
 	return is ? EXIT_SUCCESS : EXIT_FAILURE;
 }
 
+static int test_process_stat_nth(int argc, char *argv[])
+{
+	pid_t pid;
+	struct path_cxt *pc;
+	uintmax_t num = 0;
+	int n;
+
+	if (argc != 3)
+		return EXIT_FAILURE;
+	pid = strtol(argv[1], (char **) NULL, 10);
+	n = strtol(argv[2], (char **) NULL, 10);
+
+	pc = ul_new_procfs_path(pid, NULL);
+	if (!pc)
+		err(EXIT_FAILURE, "cannot alloc procfs handler");
+
+	if (procfs_process_get_stat_nth(pc, n, &num) != 0)
+		err(EXIT_FAILURE, "read %dth number failed", n);
+
+	printf("%d: %dth %ju\n", (int) pid, n, num);
+	ul_unref_path(pc);
+	return EXIT_SUCCESS;
+}
+
 int main(int argc, char *argv[])
 {
 	if (argc < 2) {
@@ -543,7 +596,8 @@ int main(int argc, char *argv[])
 				"       %1$s --fds <pid>\n"
 				"       %1$s --is-procfs [<dir>]\n"
 				"       %1$s --processes [---name <name>] [--uid <uid>]\n"
-				"       %1$s --one <pid>\n",
+				"       %1$s --one <pid>\n"
+				"       %1$s --stat-nth <pid> <n>\n",
 				program_invocation_short_name);
 		return EXIT_FAILURE;
 	}
@@ -558,6 +612,8 @@ int main(int argc, char *argv[])
 		return test_isprocfs(argc - 1, argv + 1);
 	if (strcmp(argv[1], "--one") == 0)
 		return test_one_process(argc - 1, argv + 1);
+	if (strcmp(argv[1], "--stat-nth") == 0)
+		return test_process_stat_nth(argc - 1, argv + 1);
 
 	return EXIT_FAILURE;
 }