src/system-update-generator/system-update-generator.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <unistd.h>
   5
   6 #include "fs-util.h"
   7 #include "log.h"
   8 #include "proc-cmdline.h"
   9 #include "special.h"
  10 #include "string-util.h"
  11 #include "util.h"
  12
  13 /*
  14  * Implements the logic described in systemd.offline-updates(7).
  15  */
  16
  17 static const char *arg_dest = "/tmp";
  18
  19 static int generate_symlink(void) {
  20         const char *p = NULL;
  21
  22         if (laccess("/system-update", F_OK) < 0) {
  23                 if (errno == ENOENT)
  24                         return 0;
  25
  26                 log_error_errno(errno, "Failed to check for system update: %m");
  27                 return -EINVAL;
  28         }
  29
  30         p = strjoina(arg_dest, "/" SPECIAL_DEFAULT_TARGET);
  31         if (symlink(SYSTEM_DATA_UNIT_PATH "/system-update.target", p) < 0)
  32                 return log_error_errno(errno, "Failed to create symlink %s: %m", p);
  33
  34         return 1;
  35 }
  36
  37 static int parse_proc_cmdline_item(const char *key, const char *value, void *data) {
  38         assert(key);
  39
  40         /* Check if a run level is specified on the kernel command line. The
  41          * command line has higher priority than any on-disk configuration, so
  42          * it'll make any symlink we create moot.
  43          */
  44
  45         if (streq(key, "systemd.unit") && !proc_cmdline_value_missing(key, value))
  46                 log_warning("Offline system update overridden by kernel command line systemd.unit= setting");
  47         else if (!value && runlevel_to_target(key))
  48                 log_warning("Offline system update overridden by runlevel \"%s\" on the kernel command line", key);
  49
  50         return 0;
  51 }
  52
  53 int main(int argc, char *argv[]) {
  54         int r, k;
  55
  56         if (argc > 1 && argc != 4) {
  57                 log_error("This program takes three or no arguments.");
  58                 return EXIT_FAILURE;
  59         }
  60
  61         if (argc > 1)
  62                 arg_dest = argv[2];
  63
  64         log_set_prohibit_ipc(true);
  65         log_set_target(LOG_TARGET_AUTO);
  66         log_parse_environment();
  67         log_open();
  68
  69         umask(0022);
  70
  71         r = generate_symlink();
  72
  73         if (r > 0) {
  74                 k = proc_cmdline_parse(parse_proc_cmdline_item, NULL, 0);
  75                 if (k < 0)
  76                         log_warning_errno(k, "Failed to parse kernel command line, ignoring: %m");
  77         }
  78
  79         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
  80 }