swap: listen for POLLPRI events on /proc/swaps if available

TODO

@@ -48,8 +48,6 @@
 
 * system.conf/session.conf man page
 
-* exec /sbin/poweroff as PID 1 and do the shutdown
-
 * suspend, resume
 
 * passphrase agent https://bugs.freedesktop.org/show_bug.cgi?id=30038
@@ -84,14 +82,14 @@ External:
 
 * patch kernel for cpu feature modalias for autoloading aes/kvm/...
 
+* patch fsck to support --lock
+
 * place /etc/inittab with explaining blurb.
 
 * pam_securetty should honour console=
 
 * procps, psmisc, sysvinit-tools, hostname → util-linux-ng
 
-* nologin nach /var/run https://bugzilla.redhat.com/show_bug.cgi?id=624489
-
 * make sysinit honour forcefsck/fastboot from the kernel command line fsck.mode=auto|force|skip
 
 * pam: fix double sudo session cleanup:

src/manager.c

@@ -216,7 +216,7 @@ int manager_new(ManagerRunningAs running_as, Manager **_m) {
         m->audit_fd = -1;
 #endif
 
-        m->signal_watch.fd = m->mount_watch.fd = m->udev_watch.fd = m->epoll_fd = m->dev_autofs_fd = -1;
+        m->signal_watch.fd = m->mount_watch.fd = m->udev_watch.fd = m->epoll_fd = m->dev_autofs_fd = m->swap_watch.fd = -1;
         m->current_job_id = 1; /* start as id #1, so that we can leave #0 around as "null-like" value */
 
         if (!(m->environment = strv_copy(environ)))
@@ -2171,6 +2171,11 @@ static int process_event(Manager *m, struct epoll_event *ev) {
                 mount_fd_event(m, ev->events);
                 break;
 
+        case WATCH_SWAP:
+                /* Some swap table change, intended for the swap subsystem */
+                swap_fd_event(m, ev->events);
+                break;
+
         case WATCH_UDEV:
                 /* Some notification from udev, intended for the device subsystem */
                 device_fd_event(m, ev->events);

src/manager.h

@@ -64,6 +64,7 @@ enum WatchType {
         WATCH_UNIT_TIMER,
         WATCH_JOB_TIMER,
         WATCH_MOUNT,
+        WATCH_SWAP,
         WATCH_UDEV,
         WATCH_DBUS_WATCH,
         WATCH_DBUS_TIMEOUT
@@ -161,6 +162,7 @@ struct Manager {
         FILE *proc_swaps;
         Hashmap *swaps_by_proc_swaps;
         bool request_reload;
+        Watch swap_watch;
 
         /* Data specific to the D-Bus subsystem */
         DBusConnection *api_bus, *system_bus;

src/mount.c

@@ -1526,7 +1526,7 @@ static int mount_enumerate(Manager *m) {
                 m->mount_watch.fd = fileno(m->proc_self_mountinfo);
 
                 zero(ev);
-                ev.events = EPOLLERR;
+                ev.events = EPOLLPRI;
                 ev.data.ptr = &m->mount_watch;
 
                 if (epoll_ctl(m->epoll_fd, EPOLL_CTL_ADD, m->mount_watch.fd, &ev) < 0)
@@ -1551,7 +1551,7 @@ void mount_fd_event(Manager *m, int events) {
         int r;
 
         assert(m);
-        assert(events == EPOLLERR);
+        assert(events & EPOLLPRI);
 
         /* The manager calls this for every fd event happening on the
          * /proc/self/mountinfo file, which informs us about mounting

src/swap.c

@@ -1056,16 +1056,23 @@ static int swap_load_proc_swaps(Manager *m, bool set_flags) {
 }
 
 int swap_dispatch_reload(Manager *m) {
-        Meta *meta;
-        int r;
-
-        assert(m);
+        /* This function should go as soon as the kernel properly notifies us */
 
         if (_likely_(!m->request_reload))
                 return 0;
 
         m->request_reload = false;
 
+        return swap_fd_event(m, EPOLLPRI);
+}
+
+int swap_fd_event(Manager *m, int events) {
+        Meta *meta;
+        int r;
+
+        assert(m);
+        assert(events & EPOLLPRI);
+
         if ((r == swap_load_proc_swaps(m, true)) < 0) {
                 log_error("Failed to reread /proc/swaps: %s", strerror(-r));
 
@@ -1169,12 +1176,24 @@ static void swap_shutdown(Manager *m) {
 
 static int swap_enumerate(Manager *m) {
         int r;
+        struct epoll_event ev;
         assert(m);
 
-        if (!m->proc_swaps)
+        if (!m->proc_swaps) {
                 if (!(m->proc_swaps = fopen("/proc/swaps", "re")))
                         return -errno;
 
+                m->swap_watch.type = WATCH_SWAP;
+                m->swap_watch.fd = fileno(m->proc_swaps);
+
+                zero(ev);
+                ev.events = EPOLLPRI;
+                ev.data.ptr = &m->swap_watch;
+
+                if (epoll_ctl(m->epoll_fd, EPOLL_CTL_ADD, m->swap_watch.fd, &ev) < 0)
+                        return -errno;
+        }
+
         /* We rely on mount.c to load /etc/fstab for us */
 
         if ((r = swap_load_proc_swaps(m, false)) < 0)

src/swap.h

@@ -103,6 +103,7 @@ int swap_add_one(Manager *m, const char *what, const char *what_proc_swaps, int
 int swap_add_one_mount_link(Swap *s, Mount *m);
 
 int swap_dispatch_reload(Manager *m);
+int swap_fd_event(Manager *m, int events);
 
 const char* swap_state_to_string(SwapState i);
 SwapState swap_state_from_string(const char *s);