util: add functions getting proc cwd and root

/proc/[pid]/cwd and /proc/[pid]/root are symliks to corresponding
directories

The added functions returns values of that symlinks.

src/shared/util.c

@@ -797,19 +797,30 @@ int get_process_capeff(pid_t pid, char **capeff) {
         return get_status_field(p, "\nCapEff:", capeff);
 }
 
+static int get_process_link_contents(const char *proc_file, char **name) {
+        int r;
+
+        assert(proc_file);
+        assert(name);
+
+        r = readlink_malloc(proc_file, name);
+        if (r < 0)
+                return r == -ENOENT ? -ESRCH : r;
+
+        return 0;
+}
+
 int get_process_exe(pid_t pid, char **name) {
         const char *p;
         char *d;
         int r;
 
         assert(pid >= 0);
-        assert(name);
 
         p = procfs_file_alloca(pid, "exe");
-
-        r = readlink_malloc(p, name);
+        r = get_process_link_contents(p, name);
         if (r < 0)
-                return r == -ENOENT ? -ESRCH : r;
+                return r;
 
         d = endswith(*name, " (deleted)");
         if (d)
@@ -861,6 +872,26 @@ int get_process_gid(pid_t pid, gid_t *gid) {
         return get_process_id(pid, "Gid:", gid);
 }
 
+int get_process_cwd(pid_t pid, char **cwd) {
+        const char *p;
+
+        assert(pid >= 0);
+
+        p = procfs_file_alloca(pid, "cwd");
+
+        return get_process_link_contents(p, cwd);
+}
+
+int get_process_root(pid_t pid, char **root) {
+        const char *p;
+
+        assert(pid >= 0);
+
+        p = procfs_file_alloca(pid, "root");
+
+        return get_process_link_contents(p, root);
+}
+
 char *strnappend(const char *s, const char *suffix, size_t b) {
         size_t a;
         char *r;

src/shared/util.h

@@ -295,6 +295,8 @@ int get_process_exe(pid_t pid, char **name);
 int get_process_uid(pid_t pid, uid_t *uid);
 int get_process_gid(pid_t pid, gid_t *gid);
 int get_process_capeff(pid_t pid, char **capeff);
+int get_process_cwd(pid_t pid, char **cwd);
+int get_process_root(pid_t pid, char **root);
 
 char hexchar(int x) _const_;
 int unhexchar(char c) _const_;

src/test/test-util.c

@@ -490,13 +490,14 @@ static void test_u64log2(void) {
 
 static void test_get_process_comm(void) {
         struct stat st;
-        _cleanup_free_ char *a = NULL, *c = NULL, *d = NULL, *f = NULL, *i = NULL;
+        _cleanup_free_ char *a = NULL, *c = NULL, *d = NULL, *f = NULL, *i = NULL, *cwd = NULL, *root = NULL;
         unsigned long long b;
         pid_t e;
         uid_t u;
         gid_t g;
         dev_t h;
         int r;
+        pid_t me;
 
         if (stat("/proc/1/comm", &st) == 0) {
                 assert_se(get_process_comm(1, &a) >= 0);
@@ -532,6 +533,16 @@ static void test_get_process_comm(void) {
         log_info("pid1 gid: "GID_FMT, g);
         assert_se(g == 0);
 
+        me = getpid();
+
+        r = get_process_cwd(me, &cwd);
+        assert_se(r >= 0 || r == -EACCES);
+        log_info("pid1 cwd: '%s'", cwd);
+
+        r = get_process_root(me, &root);
+        assert_se(r >= 0 || r == -EACCES);
+        log_info("pid1 root: '%s'", root);
+
         assert_se(get_ctty_devnr(1, &h) == -ENOENT);
 
         getenv_for_pid(1, "PATH", &i);