fs-util: introduce inotify_add_watch_and_warn() helper

The default message for ENOSPC is very misleading: it says that the disk is
filled, but in fact the inotify watch limit is the problem.

So let's introduce and use a wrapper that simply calls inotify_add_watch(2) and
which fixes the error message up in case ENOSPC is returned.

src/basic/fs-util.c

@@ -660,6 +660,21 @@ int inotify_add_watch_fd(int fd, int what, uint32_t mask) {
         return r;
 }
 
+int inotify_add_watch_and_warn(int fd, const char *pathname, uint32_t mask) {
+        if (inotify_add_watch(fd, pathname, mask) < 0) {
+                const char *reason;
+
+                if (errno == ENOSPC)
+                        reason = "inotify watch limit reached";
+                else
+                        reason = strerror_safe(errno);
+
+                return log_error_errno(errno, "Failed to add a watch for %s: %s", pathname, reason);
+        }
+
+        return 0;
+}
+
 static bool unsafe_transition(const struct stat *a, const struct stat *b) {
         /* Returns true if the transition from a to b is safe, i.e. that we never transition from unprivileged to
          * privileged files or directories. Why bother? So that unprivileged code can't symlink to privileged files

src/basic/fs-util.h

@@ -72,6 +72,7 @@ union inotify_event_buffer {
 };
 
 int inotify_add_watch_fd(int fd, int what, uint32_t mask);
+int inotify_add_watch_and_warn(int fd, const char *pathname, uint32_t mask);
 
 enum {
         CHASE_PREFIX_ROOT = 1 << 0, /* The specified path will be prefixed by the specified root before beginning the iteration */

src/core/manager.c

@@ -295,10 +295,12 @@ static int manager_check_ask_password(Manager *m) {
                 if (m->ask_password_inotify_fd < 0)
                         return log_error_errno(errno, "Failed to create inotify object: %m");
 
-                if (inotify_add_watch(m->ask_password_inotify_fd, "/run/systemd/ask-password", IN_CREATE|IN_DELETE|IN_MOVE) < 0) {
+                r = inotify_add_watch_and_warn(m->ask_password_inotify_fd,
-                        log_error_errno(errno, "Failed to watch \"/run/systemd/ask-password\": %m");
+                                               "/run/systemd/ask-password",
+                                               IN_CREATE|IN_DELETE|IN_MOVE);
+                if (r < 0) {
                         manager_close_ask_password(m);
-                        return -errno;
+                        return r;
                 }
 
                 r = sd_event_add_io(m->event, &m->ask_password_event_source,

src/core/path.c

@@ -89,24 +89,29 @@ int path_spec_watch(PathSpec *s, sd_event_io_handler_t handler) {
                                 break;
                         }
 
-                        r = log_warning_errno(errno, "Failed to add watch on %s: %s", s->path, errno == ENOSPC ? "too many watches" : strerror_safe(r));
+                        /* This second call to inotify_add_watch() should fail like the previous
-                        if (cut)
+                         * one and is done for logging the error in a comprehensive way. */
-                                *cut = tmp;
+                        r = inotify_add_watch_and_warn(s->inotify_fd, s->path, flags);
-                        goto fail;
+                        if (r < 0) {
-                } else {
+                                if (cut)
-                        exists = true;
+                                        *cut = tmp;
-
+                                goto fail;
-                        /* Path exists, we don't need to watch parent too closely. */
-                        if (oldslash) {
-                                char *cut2 = oldslash + (oldslash == s->path);
-                                char tmp2 = *cut2;
-                                *cut2 = '\0';
-
-                                (void) inotify_add_watch(s->inotify_fd, s->path, IN_MOVE_SELF);
-                                /* Error is ignored, the worst can happen is we get spurious events. */
-
-                                *cut2 = tmp2;
                         }
+
+                        /* Hmm, we succeeded in adding the watch this time... let's continue. */
+                }
+                exists = true;
+
+                /* Path exists, we don't need to watch parent too closely. */
+                if (oldslash) {
+                        char *cut2 = oldslash + (oldslash == s->path);
+                        char tmp2 = *cut2;
+                        *cut2 = '\0';
+
+                        (void) inotify_add_watch(s->inotify_fd, s->path, IN_MOVE_SELF);
+                        /* Error is ignored, the worst can happen is we get spurious events. */
+
+                        *cut2 = tmp2;
                 }
 
                 if (cut)

src/time-wait-sync/time-wait-sync.c

@@ -225,9 +225,9 @@ static int run(int argc, char * argv[]) {
         if (r < 0)
                 return log_error_errno(r, "Failed to create notify event source: %m");
 
-        r = inotify_add_watch(state.inotify_fd, "/run/systemd/", IN_CREATE);
+        r = inotify_add_watch_and_warn(state.inotify_fd, "/run/systemd/", IN_CREATE);
         if (r < 0)
-                return log_error_errno(errno, "Failed to watch /run/systemd/: %m");
+                return r;
 
         state.run_systemd_wd = r;
 

src/tty-ask-password-agent/tty-ask-password-agent.c

@@ -11,7 +11,6 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <string.h>
-#include <sys/inotify.h>
 #include <sys/prctl.h>
 #include <sys/signalfd.h>
 #include <sys/socket.h>
@@ -29,6 +28,7 @@
 #include "exit-status.h"
 #include "fd-util.h"
 #include "fileio.h"
+#include "fs-util.h"
 #include "hashmap.h"
 #include "io-util.h"
 #include "macro.h"
@@ -510,12 +510,9 @@ static int process_and_watch_password_files(void) {
         if (notify < 0)
                 return log_error_errno(errno, "Failed to allocate directory watch: %m");
 
-        if (inotify_add_watch(notify, "/run/systemd/ask-password", IN_CLOSE_WRITE|IN_MOVED_TO) < 0) {
+        r = inotify_add_watch_and_warn(notify, "/run/systemd/ask-password", IN_CLOSE_WRITE|IN_MOVED_TO);
-                if (errno == ENOSPC)
+        if (r < 0)
-                        return log_error_errno(errno, "Failed to add /run/systemd/ask-password to directory watch: inotify watch limit reached");
+                return r;
-                else
-                        return log_error_errno(errno, "Failed to add /run/systemd/ask-password to directory watch: %m");
-        }
 
         assert_se(sigemptyset(&mask) >= 0);
         assert_se(sigset_add_many(&mask, SIGINT, SIGTERM, -1) >= 0);