shutdownd: rework interface, allow subscribing to scheduled shutdowns

This extends the shutdownd interface to expose schedule shutdown
information in /run/systemd/shutdown/schedule.

This also cleans up the shutdownd protocol and documents it in a header
file sd-shutdown.h.

This is supposed to be used by client code that wants to control and
monitor scheduled shutdown.

1 files changed, 108 insertions, 0 deletions

diff --git a/src/systemd/sd-shutdown.h b/src/systemd/sd-shutdown.h
new file mode 100644
index 000000000..29fcf3417
--- /dev/null
+++ b/src/systemd/sd-shutdown.h
@@ -0,0 +1,108 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#ifndef foosdshutdownhfoo
+#define foosdshutdownhfoo
+
+/***
+  This file is part of systemd.
+
+  Copyright 2010 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+/* Interface for scheduling and cancelling timed shutdowns. */
+
+#include <inttypes.h>
+
+typedef enum sd_shutdown_mode {
+        SD_SHUTDOWN_NONE = 0,
+        SD_SHUTDOWN_REBOOT = 'r',
+        SD_SHUTDOWN_POWEROFF = 'P',
+        SD_SHUTDOWN_HALT = 'H',
+        SD_SHUTDOWN_KEXEC = 'K'
+} sd_shutdown_mode_t;
+
+/* Calculate the size of the message as "offsetof(struct
+ * sd_shutdown_command, wall_message) +
+ * strlen(command.wall_message)" */
+__attribute__((packed)) struct sd_shutdown_command {
+        /* Microseconds after the epoch 1970 UTC */
+        uint64_t usec;
+
+        /* H, P, r, i.e. the switches usually passed to
+         * /usr/bin/shutdown to select whether to halt, power-off or
+         * reboot the machine */
+        sd_shutdown_mode_t mode:8;
+
+        /* If non-zero, don't actually shut down, just pretend */
+        unsigned dry_run:1;
+
+        /* If non-zero, send our wall message */
+        unsigned warn_wall:1;
+
+        /* The wall message to send around. Leave empty for the
+         * default wall message */
+        char wall_message[];
+};
+
+/* The scheme is very simple:
+ *
+ * To schedule a shutdown, simply fill in and send a single
+ * AF_UNIX/SOCK_DGRAM datagram with the structure above suffixed with
+ * the wall message to the socket /run/systemd/shutdownd (leave an
+ * empty wall message for the default shutdown message). To calculate
+ * the size of the message use "offsetof(struct sd_shutdown_command,
+ * wall_message) + strlen(command.wall_message)".
+ *
+ * To cancel a shutdown, do the same, but send an fully zeroed out
+ * structure.
+ *
+ * To be notified about scheduled shutdowns, create an inotify watch
+ * on /run/shutdown/. Whenever a file called "scheduled" appears a
+ * shutdown is scheduled. If it is removed it is canceled. It is
+ * replaced the scheduled shutdown has been changed. The file contains
+ * a simple environment-like block, that contains information about
+ * the scheduled shutdown:
+ *
+ * USEC=
+ * encodes the time for the shutdown in usecs since the epoch UTC,
+ * formatted as numeric string.
+ *
+ * WARN_WALL=
+ * is 1 if a wall message shall be sent
+ *
+ * DRY_RUN=
+ * is 1 if a dry run shutdown is scheduled
+ *
+ * MODE=
+ * is the shutdown mode, one of "poweroff", "reboot", "halt", "kexec"
+ *
+ * WALL_MESSAGE=
+ * is the wall message to use, with all special characters escape in C style.
+ *
+ * Note that some fields might be missing if they do not apply.
+ *
+ * Note that the file is first written to a temporary file and then
+ * renamed, in order to provide atomic properties for readers: if the
+ * file exists under the name "scheduled" it is guaranteed to be fully
+ * written. A reader should ignore all files in that directory by any
+ * other name.
+ *
+ * Scheduled shutdowns are only accepted from privileged processes,
+ * but the directory may be watched and the file in it read by
+ * anybody.
+ */
+
+#endif