Several fixes and cleanups around sd_listen_fds() (#36788)

src/initctl/initctl.c

@@ -318,8 +318,7 @@ static int run(int argc, char *argv[]) {
 
         n = sd_listen_fds(true);
         if (n < 0)
-                return log_error_errno(errno,
-                                       "Failed to read listening file descriptors from environment: %m");
+                return log_error_errno(n, "Failed to read listening file descriptors from environment: %m");
 
         if (n <= 0 || n > SERVER_FD_MAX)
                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL),

src/libsystemd/sd-varlink/sd-varlink.c

@@ -3753,7 +3753,7 @@ _public_ int sd_varlink_server_add_connection_stdio(sd_varlink_server *s, sd_var
 
 _public_ int sd_varlink_server_listen_name(sd_varlink_server *s, const char *name) {
         _cleanup_strv_free_ char **names = NULL;
-        int r, n = 0;
+        int r, m, n = 0;
 
         assert_return(s, -EINVAL);
         assert_return(name, -EINVAL);
@@ -3764,11 +3764,11 @@ _public_ int sd_varlink_server_listen_name(sd_varlink_server *s, const char *nam
          * See https://varlink.org/#activation for the environment variables this is backed by and the
          * recommended "varlink" identifier in $LISTEN_FDNAMES. */
 
-        r = sd_listen_fds_with_names(/* unset_environment= */ false, &names);
-        if (r < 0)
-                return r;
+        m = sd_listen_fds_with_names(/* unset_environment= */ false, &names);
+        if (m < 0)
+                return m;
 
-        for (int i = 0; i < r; i++) {
+        for (int i = 0; i < m; i++) {
                 int b, fd;
                 socklen_t l = sizeof(b);
 

src/nspawn/nspawn.c

@@ -5970,7 +5970,7 @@ static int run(int argc, char *argv[]) {
         bool remove_directory = false, remove_image = false, veth_created = false;
         _cleanup_close_ int master = -EBADF, userns_fd = -EBADF, mount_fd = -EBADF;
         _cleanup_fdset_free_ FDSet *fds = NULL;
-        int r, n_fd_passed, ret = EXIT_SUCCESS;
+        int r, ret = EXIT_SUCCESS;
         char veth_name[IFNAMSIZ] = "";
         struct ExposeArgs expose_args = {};
         _cleanup_(release_lock_file) LockFile tree_global_lock = LOCK_FILE_INIT, tree_local_lock = LOCK_FILE_INIT;
@@ -6057,13 +6057,10 @@ static int run(int argc, char *argv[]) {
          * so just turning this off here means we only turn it off in nspawn itself, not any children. */
         (void) ignore_signals(SIGPIPE);
 
-        n_fd_passed = sd_listen_fds(false);
-        if (n_fd_passed > 0) {
-                r = fdset_new_listen_fds(&fds, false);
-                if (r < 0) {
-                        log_error_errno(r, "Failed to collect file descriptors: %m");
-                        goto finish;
-                }
+        r = fdset_new_listen_fds(&fds, /* unset = */ false);
+        if (r < 0) {
+                log_error_errno(r, "Failed to collect file descriptors: %m");
+                goto finish;
         }
 
         /* The "default" umask. This is appropriate for most file and directory

src/oom/oomd.c

@@ -115,10 +115,12 @@ static int run(int argc, char *argv[]) {
          * requirements do not have a reliable means to check for in code. */
 
         int n = sd_listen_fds(0);
+        if (n < 0)
+                return log_error_errno(n, "Failed to determine number of listening fds: %m");
         if (n > 1)
                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Received too many file descriptors");
 
-        int fd = n == 1 ? SD_LISTEN_FDS_START : -1;
+        int fd = n == 1 ? SD_LISTEN_FDS_START : -EBADF;
 
         /* SwapTotal is always available in /proc/meminfo and defaults to 0, even on swap-disabled kernels. */
         r = get_proc_field("/proc/meminfo", "SwapTotal", WHITESPACE, &swap);

src/shared/fdset.c

@@ -254,25 +254,32 @@ int fdset_cloexec(FDSet *fds, bool b) {
 
 int fdset_new_listen_fds(FDSet **ret, bool unset) {
         _cleanup_(fdset_shallow_freep) FDSet *s = NULL;
-        int n, fd, r;
+        int n, r;
 
         assert(ret);
 
         /* Creates an fdset and fills in all passed file descriptors */
 
+        n = sd_listen_fds(unset);
+        if (n < 0)
+                return n;
+        if (n == 0) {
+                *ret = NULL;
+                return 0;
+        }
+
         s = fdset_new();
         if (!s)
                 return -ENOMEM;
 
-        n = sd_listen_fds(unset);
-        for (fd = SD_LISTEN_FDS_START; fd < SD_LISTEN_FDS_START + n; fd++) {
+        for (int fd = SD_LISTEN_FDS_START; fd < SD_LISTEN_FDS_START + n; fd++) {
                 r = fdset_put(s, fd);
                 if (r < 0)
                         return r;
         }
 
         *ret = TAKE_PTR(s);
-        return 0;
+        return n;
 }
 
 int fdset_to_array(FDSet *fds, int **ret) {

src/vmspawn/vmspawn.c

@@ -2513,11 +2513,11 @@ static int run(int argc, char *argv[]) {
                                  glyph(GLYPH_LIGHT_SHADE), ansi_grey(), ansi_highlight(), ansi_grey(), ansi_normal());
         }
 
-        r = sd_listen_fds_with_names(true, &names);
-        if (r < 0)
-                return log_error_errno(r, "Failed to get passed file descriptors: %m");
+        int n = sd_listen_fds_with_names(true, &names);
+        if (n < 0)
+                return log_error_errno(n, "Failed to get passed file descriptors: %m");
 
-        for (int i = 0; i < r; i++) {
+        for (int i = 0; i < n; i++) {
                 int fd = SD_LISTEN_FDS_START + i;
                 if (streq(names[i], "kvm"))
                         kvm_device_fd = fd;