ip vrf: Add command name next to pid

'ip vrf pids' is used to list processes bound to a vrf, but it only
shows the pid leaving a lot of work for the user. Add the command
name to the output. With this patch you get the more user friendly:

    $ ip vrf pids mgmt
     1121  ntpd
     1418  gdm-session-wor
     1488  gnome-session
     1491  dbus-launch
     1492  dbus-daemon
     1565  sshd
     ...

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>

include/utils.h

@@ -260,5 +260,6 @@ int get_real_family(int rtm_type, int rtm_family);
 int cmd_exec(const char *cmd, char **argv, bool do_fork);
 int make_path(const char *path, mode_t mode);
 char *find_cgroup2_mount(void);
+int get_command_name(const char *pid, char *comm, size_t len);
 
 #endif /* __UTILS_H__ */

ip/ipvrf.c

@@ -111,27 +111,31 @@ static void read_cgroup_pids(const char *base_path, char *name)
 {
 	char path[PATH_MAX];
 	char buf[4096];
-	ssize_t n;
-	int fd;
+	FILE *fp;
 
 	if (snprintf(path, sizeof(path), "%s/vrf/%s%s",
 		     base_path, name, CGRP_PROC_FILE) >= sizeof(path))
 		return;
 
-	fd = open(path, O_RDONLY);
-	if (fd < 0)
+	fp = fopen(path, "r");
+	if (!fp)
 		return; /* no cgroup file, nothing to show */
 
 	/* dump contents (pids) of cgroup.procs */
-	while (1) {
-		n = read(fd, buf, sizeof(buf) - 1);
-		if (n <= 0)
-			break;
+	while (fgets(buf, sizeof(buf), fp)) {
+		char *nl, comm[32];
 
-		printf("%s", buf);
+		nl = strchr(buf, '\n');
+		if (nl)
+			*nl = '\0';
+
+		if (get_command_name(buf, comm, sizeof(comm)))
+			strcpy(comm, "<terminated?>");
+
+		printf("%5s  %s\n", buf, comm);
 	}
 
-	close(fd);
+	fclose(fp);
 }
 
 /* recurse path looking for PATH[/NETNS]/vrf/NAME */

lib/fs.c

@@ -14,6 +14,7 @@
 #include <sys/stat.h>
 #include <sys/socket.h>
 #include <sys/mount.h>
+#include <ctype.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -149,3 +150,44 @@ out:
 
 	return rc;
 }
+
+int get_command_name(const char *pid, char *comm, size_t len)
+{
+	char path[PATH_MAX];
+	char line[128];
+	FILE *fp;
+
+	if (snprintf(path, sizeof(path),
+		     "/proc/%s/status", pid) >= sizeof(path)) {
+		return -1;
+	}
+
+	fp = fopen(path, "r");
+	if (!fp)
+		return -1;
+
+	comm[0] = '\0';
+	while (fgets(line, sizeof(line), fp)) {
+		char *nl, *name;
+
+		name = strstr(line, "Name:");
+		if (!name)
+			continue;
+
+		name += 5;
+		while (isspace(*name))
+			name++;
+
+		nl = strchr(name, '\n');
+		if (nl)
+			*nl = '\0';
+
+		strncpy(comm, name, len - 1);
+		comm[len - 1] = '\0';
+		break;
+	}
+
+	fclose(fp);
+
+	return 0;
+}