Move various files that don't need to be in basic/ to shared/

This doesn't have much effect on the final build, because we link libbasic.a
into libsystemd-shared.so, so in the end, all the object built from basic/
end up in libsystemd-shared. And when the static library is linked into binaries,
any objects that are included in it but are not used are trimmed. Hence, the
size of output artifacts doesn't change:

$ du -sb /var/tmp/inst*
54181861	/var/tmp/inst1    (old)
54207441	/var/tmp/inst1s   (old split-usr)
54182477	/var/tmp/inst2    (new)
54208041	/var/tmp/inst2s   (new split-usr)

(The negligible change in size is because libsystemd-shared.so is bigger
by a few hundred bytes. I guess it's because symbols are named differently
or something like that.)

The effect is on the build process, in particular partial builds. This change
effectively moves the requirements on some build steps toward the leaves of the
dependency tree. Two effects:
- when building items that do not depend on libsystemd-shared, we
  build less stuff for libbasic.a (which wouldn't be used anyway,
  so it's a net win).
- when building items that do depend on libshared, we reduce libbasic.a as a
  synchronization point, possibly allowing better parallelism.

Method:
1. copy list of .h files from src/basic/meson.build to /tmp/basic
2. $ for i in $(grep '.h$' /tmp/basic); do echo $i; git --no-pager grep "include \"$i\"" src/basic/ 'src/lib*' 'src/nss-*' 'src/journal/sd-journal.c' |grep -v "${i%.h}.c";echo ;done | less

1 files changed, 83 insertions, 0 deletions

diff --git a/src/shared/reboot-util.c b/src/shared/reboot-util.c
new file mode 100644
index 0000000000..ca40159b96
--- /dev/null
+++ b/src/shared/reboot-util.c
@@ -0,0 +1,83 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <errno.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "fileio.h"
+#include "log.h"
+#include "raw-reboot.h"
+#include "reboot-util.h"
+#include "string-util.h"
+#include "umask-util.h"
+#include "virt.h"
+
+int update_reboot_parameter_and_warn(const char *parameter) {
+        int r;
+
+        if (isempty(parameter)) {
+                if (unlink("/run/systemd/reboot-param") < 0) {
+                        if (errno == ENOENT)
+                                return 0;
+
+                        return log_warning_errno(errno, "Failed to unlink reboot parameter file: %m");
+                }
+
+                return 0;
+        }
+
+        RUN_WITH_UMASK(0022) {
+                r = write_string_file("/run/systemd/reboot-param", parameter,
+                                      WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_ATOMIC);
+                if (r < 0)
+                        return log_warning_errno(r, "Failed to write reboot parameter file: %m");
+        }
+
+        return 0;
+}
+
+int reboot_with_parameter(RebootFlags flags) {
+        int r;
+
+        /* Reboots the system with a parameter that is read from /run/systemd/reboot-param. Returns 0 if REBOOT_DRY_RUN
+         * was set and the actual reboot operation was hence skipped. If REBOOT_FALLBACK is set and the reboot with
+         * parameter doesn't work out a fallback to classic reboot() is attempted. If REBOOT_FALLBACK is not set, 0 is
+         * returned instead, which should be considered indication for the caller to fall back to reboot() on its own,
+         * or somehow else deal with this. If REBOOT_LOG is specified will log about what it is going to do, as well as
+         * all errors. */
+
+        if (detect_container() == 0) {
+                _cleanup_free_ char *parameter = NULL;
+
+                r = read_one_line_file("/run/systemd/reboot-param", &parameter);
+                if (r < 0 && r != -ENOENT)
+                        log_full_errno(flags & REBOOT_LOG ? LOG_WARNING : LOG_DEBUG, r,
+                                       "Failed to read reboot parameter file, ignoring: %m");
+
+                if (!isempty(parameter)) {
+
+                        log_full(flags & REBOOT_LOG ? LOG_INFO : LOG_DEBUG,
+                                 "Rebooting with argument '%s'.", parameter);
+
+                        if (flags & REBOOT_DRY_RUN)
+                                return 0;
+
+                        (void) raw_reboot(LINUX_REBOOT_CMD_RESTART2, parameter);
+
+                        log_full_errno(flags & REBOOT_LOG ? LOG_WARNING : LOG_DEBUG, errno,
+                                       "Failed to reboot with parameter, retrying without: %m");
+                }
+        }
+
+        if (!(flags & REBOOT_FALLBACK))
+                return 0;
+
+        log_full(flags & REBOOT_LOG ? LOG_INFO : LOG_DEBUG, "Rebooting.");
+
+        if (flags & REBOOT_DRY_RUN)
+                return 0;
+
+        (void) reboot(RB_AUTOBOOT);
+
+        return log_full_errno(flags & REBOOT_LOG ? LOG_ERR : LOG_DEBUG, errno, "Failed to reboot: %m");
+}