main: introduce /etc/machine-id

This is supposed to play the same roles /var/lib/dbus/machine-id,
however fixes a couple of problems:

- It is available during early boot since it is stored in /etc

- Removes the ID from the D-Bus context and moves it into a system
  context, thus hopefully lowering hesitation by people to use it.

- It is generated at installation time. If the file is empty at boot
  time it will be mounted over with a randomly generated ID, which is
  not saved to disk. This is useful to support state-less machines with
  no transient or writable /etc configuration.

1 files changed, 166 insertions, 0 deletions

diff --git a/src/machine-id-setup.c b/src/machine-id-setup.c
new file mode 100644
index 0000000000..940670b339
--- /dev/null
+++ b/src/machine-id-setup.c
@@ -0,0 +1,166 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  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/>.
+***/
+
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <sys/mount.h>
+
+#include "machine-id-setup.h"
+#include "macro.h"
+#include "util.h"
+#include "log.h"
+
+static int generate(char id[34]) {
+        int fd;
+        char buf[16];
+        char *p, *q;
+        ssize_t k;
+
+        assert(id);
+
+        /* First, try reading the D-Bus machine id, unless it is a symlink */
+        if ((fd = open("/var/lib/dbus/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW)) >= 0) {
+
+                k = loop_read(fd, id, 33, false);
+                close_nointr_nofail(fd);
+
+                if (k >= 32) {
+                        id[32] = '\n';
+                        id[33] = 0;
+
+                        log_info("Initializing machine ID from D-Bus machine ID.");
+                        return 0;
+                }
+        }
+
+        /* If that didn't work, generate a random machine id */
+        if ((fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY)) < 0) {
+                log_error("Failed to open /dev/urandom: %m");
+                return -errno;
+        }
+
+        k = loop_read(fd, buf, sizeof(buf), false);
+        close_nointr_nofail(fd);
+
+        if (k != sizeof(buf)) {
+                log_error("Failed to read /dev/urandom: %s", strerror(k < 0 ? -k : EIO));
+                return k < 0 ? (int) k : -EIO;
+        }
+
+        for (p = buf, q = id; p < buf + sizeof(buf); p++, q += 2) {
+                q[0] = hexchar(*p >> 4);
+                q[1] = hexchar(*p & 15);
+        }
+
+        id[32] = '\n';
+        id[33] = 0;
+
+        log_info("Initializing machine ID from random generator.");
+
+        return 0;
+}
+
+int machine_id_setup(void) {
+        int fd, r;
+        bool writable;
+        struct stat st;
+        char id[34]; /* 32 + \n + \0 */
+        mode_t m;
+
+        m = umask(0000);
+
+        if ((fd = open("/etc/machine-id", O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0644)) >= 0)
+                writable = true;
+        else {
+                if ((fd = open("/etc/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY)) < 0) {
+                        umask(m);
+                        log_error("Cannot open /etc/machine-id: %m");
+                        return -errno;
+                }
+
+                writable = false;
+        }
+
+        umask(m);
+
+        if (fstat(fd, &st) < 0) {
+                log_error("fstat() failed: %m");
+                r = -errno;
+                goto finish;
+        }
+
+        if (S_ISREG(st.st_mode)) {
+                if (loop_read(fd, id, 32, false) >= 32) {
+                        r = 0;
+                        goto finish;
+                }
+        }
+
+        /* Hmm, so, the id currently stored is not useful, then let's
+         * generate one */
+
+        if ((r = generate(id)) < 0)
+                goto finish;
+
+        if (S_ISREG(st.st_mode) && writable) {
+                lseek(fd, 0, SEEK_SET);
+
+                if (loop_write(fd, id, 33, false) == 33) {
+                        r = 0;
+                        goto finish;
+                }
+        }
+
+        close_nointr_nofail(fd);
+        fd = -1;
+
+        /* Hmm, we couldn't write it? So let's write it to
+         * /dev/.systemd/machine-id as a replacement */
+
+        mkdir_p("/dev/.systemd", 0755);
+
+        if ((r = write_one_line_file("/dev/.systemd/machine-id", id)) < 0) {
+                log_error("Cannot write /dev/.systemd/machine-id: %s", strerror(-r));
+
+                unlink("/dev/.systemd/machine-id");
+                goto finish;
+        }
+
+        /* And now, let's mount it over */
+        r = mount("/dev/.systemd/machine-id", "/etc/machine-id", "bind", MS_BIND|MS_RDONLY, NULL) < 0 ? -errno : 0;
+        unlink("/dev/.systemd/machine-id");
+
+        if (r < 0)
+                log_error("Failed to mount /etc/machine-id: %s", strerror(-r));
+        else
+                log_info("Installed non-transient /etc/machine-id file.");
+
+finish:
+
+        if (fd >= 0)
+                close_nointr_nofail(fd);
+
+        return r;
+}