io-util: make flush_fd() return how many bytes where flushed

This is useful so that callers know whether anything at all and how much
was flushed.

This patches through users of this functions to ensure that the return
values > 0 which may be returned now are not propagated in public APIs.

Also, users that ignore the return value are changed to do so explicitly
now.

src/basic/io-util.c

@@ -33,6 +33,7 @@ int flush_fd(int fd) {
                 .fd = fd,
                 .events = POLLIN,
         };
+        int count = 0;
 
         /* Read from the specified file descriptor, until POLLIN is not set anymore, throwing away everything
          * read. Note that some file descriptors (notable IP sockets) will trigger POLLIN even when no data can be read
@@ -52,7 +53,7 @@ int flush_fd(int fd) {
                         return -errno;
 
                 } else if (r == 0)
-                        return 0;
+                        return count;
 
                 l = read(fd, buf, sizeof(buf));
                 if (l < 0) {
@@ -61,11 +62,13 @@ int flush_fd(int fd) {
                                 continue;
 
                         if (errno == EAGAIN)
-                                return 0;
+                                return count;
 
                         return -errno;
                 } else if (l == 0)
-                        return 0;
+                        return count;
+
+                count += (int) l;
         }
 }
 

src/core/manager.c

@@ -263,7 +263,7 @@ static int manager_dispatch_ask_password_fd(sd_event_source *source,
 
         assert(m);
 
-        flush_fd(fd);
+        (void) flush_fd(fd);
 
         m->have_ask_password = have_ask_password();
         if (m->have_ask_password < 0)

src/libsystemd/sd-login/sd-login.c

@@ -1061,10 +1061,15 @@ _public_ sd_login_monitor* sd_login_monitor_unref(sd_login_monitor *m) {
 }
 
 _public_ int sd_login_monitor_flush(sd_login_monitor *m) {
+        int r;
 
         assert_return(m, -EINVAL);
 
-        return flush_fd(MONITOR_TO_FD(m));
+        r = flush_fd(MONITOR_TO_FD(m));
+        if (r < 0)
+                return r;
+
+        return 0;
 }
 
 _public_ int sd_login_monitor_get_fd(sd_login_monitor *m) {

src/libudev/libudev-queue.c

@@ -268,8 +268,16 @@ _public_ int udev_queue_get_fd(struct udev_queue *udev_queue) {
  * Returns: the result of clearing the watch for queue changes.
  */
 _public_ int udev_queue_flush(struct udev_queue *udev_queue) {
+        int r;
+
+        assert(udev_queue);
+
         if (udev_queue->fd < 0)
                 return -EINVAL;
 
-        return flush_fd(udev_queue->fd);
+        r = flush_fd(udev_queue->fd);
+        if (r < 0)
+                return r;
+
+        return 0;
 }

src/shared/ask-password-api.c

@@ -316,7 +316,7 @@ int ask_password_tty(
                 }
 
                 if (notify >= 0 && pollfd[POLL_INOTIFY].revents != 0)
-                        flush_fd(notify);
+                        (void) flush_fd(notify);
 
                 if (pollfd[POLL_TTY].revents == 0)
                         continue;

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

@@ -159,7 +159,7 @@ static int ask_password_plymouth(
                 }
 
                 if (notify >= 0 && pollfd[POLL_INOTIFY].revents != 0)
-                        flush_fd(notify);
+                        (void) flush_fd(notify);
 
                 if (pollfd[POLL_SOCKET].revents == 0)
                         continue;