varlink-util: add varlink_execute_directory() flavour that returns unconnectable sockets

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

@@ -21,6 +21,7 @@
 #include "rm-rf.h"
 #include "socket-util.h"
 #include "string-util.h"
+#include "strv.h"
 #include "tests.h"
 #include "time-util.h"
 #include "tmpfile-util.h"
@@ -1515,6 +1516,20 @@ static int execute_dir_client_fiber(void *arg) {
                                      a->reply_count), (ssize_t) a->n_servers);
         ASSERT_EQ(*a->reply_count, a->n_servers);
 
+        /* Sockets that have a live listener must be counted as contacted, not as offline. */
+        _cleanup_strv_free_ char **offline = NULL;
+        ASSERT_OK_EQ(varlink_execute_directory_full(
+                                     a->tmpdir,
+                                     "io.test.ExecDirPing",
+                                     /* parameters= */ NULL,
+                                     /* more= */ false,
+                                     /* timeout_usec= */ USEC_INFINITY,
+                                     execute_dir_reply,
+                                     a->reply_count,
+                                     &offline), (ssize_t) a->n_servers);
+        ASSERT_TRUE(strv_isempty(offline));
+        ASSERT_EQ(*a->reply_count, 2 * a->n_servers);
+
         /* Calling the helper against a non-existent directory must fail. */
         _cleanup_free_ char *nope = NULL;
         ASSERT_OK(asprintf(&nope, "%s/does-not-exist", a->tmpdir));
@@ -1542,6 +1557,33 @@ static int execute_dir_client_fiber(void *arg) {
                                        a->reply_count));
         ASSERT_EQ(*a->reply_count, count_before);
 
+        ASSERT_OK_ZERO(varlink_execute_directory_full(
+                                       empty,
+                                       "io.test.ExecDirPing",
+                                       /* parameters= */ NULL,
+                                       /* more= */ false,
+                                       /* timeout_usec= */ USEC_INFINITY,
+                                       execute_dir_reply,
+                                       a->reply_count,
+                                       &offline));
+        ASSERT_TRUE(strv_isempty(offline));
+
+        /* A socket inode nobody listens on must not be counted as contacted, but as offline. */
+        _cleanup_free_ char *dead = ASSERT_PTR(path_join(empty, "dead"));
+        ASSERT_OK_ERRNO(mknod(dead, S_IFSOCK|0600, 0));
+
+        ASSERT_OK_ZERO(varlink_execute_directory_full(
+                                       empty,
+                                       "io.test.ExecDirPing",
+                                       /* parameters= */ NULL,
+                                       /* more= */ false,
+                                       /* timeout_usec= */ USEC_INFINITY,
+                                       execute_dir_reply,
+                                       a->reply_count,
+                                       &offline));
+        ASSERT_TRUE(strv_equal(offline, STRV_MAKE("dead")));
+        ASSERT_EQ(*a->reply_count, count_before);
+
         ASSERT_OK(sd_event_exit(sd_fiber_get_event(), EXIT_SUCCESS));
         return 0;
 }

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

@@ -13,6 +13,7 @@
 #include "set.h"
 #include "socket-util.h"
 #include "string-util.h"
+#include "strv.h"
 #include "varlink-internal.h"
 #include "varlink-util.h"
 #include "version.h"
@@ -245,14 +246,15 @@ static int varlink_finish_idle(Set *s) {
 
 #define VARLINK_EXECUTE_SOCKETS_MAX 255
 
-ssize_t varlink_execute_directory(
+ssize_t varlink_execute_directory_full(
                 const char *path,
                 const char *method,
                 sd_json_variant *parameters,
                 bool more,
                 usec_t timeout_usec,
                 sd_varlink_reply_t reply,
-                void *userdata) {
+                void *userdata,
+                char ***ret_offline_sockets) {
 
         int r;
 
@@ -262,7 +264,10 @@ ssize_t varlink_execute_directory(
         /* Invokes the specified method on all Varlink sockets in the specified directory. Any reply
          * will be dispatched to the reply callback. Blocks until the last reply has come in.
          *
-         * Returns how many sockets were contacted.
+         * Returns how many sockets were contacted. If ret_offline_sockets is non-NULL it is set to the
+         * names of the sockets that exist in the directory but could not be contacted (because nobody
+         * listens on them, or because there are too many of them). This allows callers to distinguish
+         * "nobody there" from "somebody there, but not reachable".
          *
          * Usecase for all of this: hook directories, where components can link their sockets into to get
          * notified about certain system events. */
@@ -278,6 +283,7 @@ ssize_t varlink_execute_directory(
 
         _cleanup_(sd_event_unrefp) sd_event *event = NULL;
         _cleanup_(set_freep) Set *links = NULL;
+        _cleanup_strv_free_ char **offline = NULL;
         size_t t = 0;
         FOREACH_ARRAY(dp, dentries->entries, dentries->n_entries) {
                 struct dirent *de = *dp;
@@ -290,6 +296,8 @@ ssize_t varlink_execute_directory(
 
                 if (set_size(links) >= VARLINK_EXECUTE_SOCKETS_MAX) {
                         log_debug("Too many sockets (%zu) in directory, skipping '%s'.", t, j);
+                        if (ret_offline_sockets && strv_extend(&offline, de->d_name) < 0)
+                                return log_oom_debug();
                         continue;
                 }
 
@@ -300,6 +308,8 @@ ssize_t varlink_execute_directory(
                 r = connect_unix_path(socket_fd, fd, de->d_name);
                 if (r < 0) {
                         log_debug_errno(r, "Failed to connect to '%s', ignoring: %m", j);
+                        if (ret_offline_sockets && strv_extend(&offline, de->d_name) < 0)
+                                return log_oom_debug();
                         continue;
                 }
 
@@ -377,5 +387,8 @@ ssize_t varlink_execute_directory(
                         return r;
         }
 
+        if (ret_offline_sockets)
+                *ret_offline_sockets = TAKE_PTR(offline);
+
         return (ssize_t) c;
 }

src/libsystemd/sd-varlink/varlink-util.h

@@ -34,4 +34,7 @@ int varlink_check_privileged_peer(sd_varlink *vl);
 
 extern const struct hash_ops varlink_hash_ops;
 
-ssize_t varlink_execute_directory(const char *path, const char *method, sd_json_variant *parameters, bool more, usec_t timeout_usec, sd_varlink_reply_t reply, void *userdata);
+ssize_t varlink_execute_directory_full(const char *path, const char *method, sd_json_variant *parameters, bool more, usec_t timeout_usec, sd_varlink_reply_t reply, void *userdata, char ***ret_offline_sockets);
+static inline ssize_t varlink_execute_directory(const char *path, const char *method, sd_json_variant *parameters, bool more, usec_t timeout_usec, sd_varlink_reply_t reply, void *userdata) {
+        return varlink_execute_directory_full(path, method, parameters, more, timeout_usec, reply, userdata, /* ret_offline_sockets= */ NULL);
+}