src/lighttpd-angel.c

   1 #include "first.h"
   2
   3 /**
   4  * angel process for lighttpd
   5  *
   6  * the purpose is the run as root all the time and handle:
   7  * - restart on crash
   8  * - spawn on HUP to allow graceful restart
   9  * - ...
  10  *
  11  * it has to stay safe and small to be trustable
  12  */
  13
  14 #include <sys/wait.h>
  15
  16 #include <stdlib.h>
  17 #include <stdio.h>
  18 #include <string.h>
  19 #include <errno.h>
  20 #include <unistd.h>
  21 #include <time.h>
  22 #include <signal.h>
  23
  24 #define BINPATH SBIN_DIR"/lighttpd"
  25
  26 static siginfo_t last_sigterm_info;
  27 static siginfo_t last_sighup_info;
  28
  29 static volatile sig_atomic_t start_process    = 1;
  30 static volatile pid_t pid = -1;
  31
  32 #define UNUSED(x) ( (void)(x) )
  33
  34 static void sigaction_handler(int sig, siginfo_t *si, void *context) {
  35         int exitcode;
  36
  37         UNUSED(context);
  38         switch (sig) {
  39         case SIGINT:
  40         case SIGTERM:
  41                 memcpy(&last_sigterm_info, si, sizeof(*si));
  42
  43                 /** forward the sig to the child */
  44                 kill(pid, sig);
  45                 break;
  46         case SIGHUP: /** do a graceful restart */
  47                 memcpy(&last_sighup_info, si, sizeof(*si));
  48
  49                 /** do a graceful shutdown on the main process and start a new child */
  50                 kill(pid, SIGINT);
  51
  52                 usleep(5 * 1000); /** wait 5 microsec */
  53
  54                 start_process = 1;
  55                 break;
  56         case SIGCHLD:
  57                 /** a child died, de-combie it */
  58                 wait(&exitcode);
  59                 break;
  60         }
  61 }
  62
  63 int main(int argc, char **argv) {
  64         int is_shutdown = 0;
  65         struct sigaction act;
  66
  67         UNUSED(argc);
  68
  69         /**
  70          * we are running as root BEWARE
  71          */
  72
  73         memset(&act, 0, sizeof(act));
  74         act.sa_handler = SIG_IGN;
  75         sigaction(SIGPIPE, &act, NULL);
  76         sigaction(SIGUSR1, &act, NULL);
  77
  78         act.sa_sigaction = sigaction_handler;
  79         sigemptyset(&act.sa_mask);
  80         act.sa_flags = SA_SIGINFO;
  81
  82         sigaction(SIGINT,  &act, NULL);
  83         sigaction(SIGTERM, &act, NULL);
  84         sigaction(SIGHUP,  &act, NULL);
  85         sigaction(SIGALRM, &act, NULL);
  86         sigaction(SIGCHLD, &act, NULL);
  87
  88         /* check that the compiled in path has the right user,
  89          *
  90          * BEWARE: there is a race between the check here and the exec later
  91          */
  92
  93         while (!is_shutdown) {
  94                 int exitcode = 0;
  95
  96                 if (start_process) {
  97                         pid = fork();
  98
  99                         if (0 == pid) {
 100                                 /* i'm the child */
 101
 102                                 argv[0] = BINPATH;
 103
 104                                 execvp(BINPATH, argv);
 105
 106                                 exit(1);
 107                         } else if (-1 == pid) {
 108                                 /** error */
 109
 110                                 return -1;
 111                         }
 112
 113                         /* I'm the angel */
 114                         start_process = 0;
 115                 }
 116
 117                 if ((pid_t)-1 == waitpid(pid, &exitcode, 0)) {
 118                         switch (errno) {
 119                         case EINTR:
 120                                 /* someone sent a signal ...
 121                                  * do we have to shutdown or restart the process */
 122                                 break;
 123                         case ECHILD:
 124                                 /**
 125                                  * make sure we are not in a race between the signal handler
 126                                  * and the process restart */
 127                                 if (!start_process) is_shutdown = 1;
 128                                 break;
 129                         default:
 130                                 break;
 131                         }
 132                 } else {
 133                         /** process went away */
 134
 135                         if (WIFEXITED(exitcode)) {
 136                                 /** normal exit */
 137
 138                                 is_shutdown = 1;
 139
 140                                 fprintf(stderr, "%s.%d: child (pid=%d) exited normally with exitcode: %d\n",
 141                                                 __FILE__, __LINE__,
 142                                                 pid,
 143                                                 WEXITSTATUS(exitcode));
 144
 145                         } else if (WIFSIGNALED(exitcode)) {
 146                                 /** got a signal */
 147
 148                                 fprintf(stderr, "%s.%d: child (pid=%d) exited unexpectedly with signal %d, restarting\n",
 149                                                 __FILE__, __LINE__,
 150                                                 pid,
 151                                                 WTERMSIG(exitcode));
 152
 153                                 start_process = 1;
 154                         }
 155                 }
 156         }
 157
 158         return 0;
 159 }
 160