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         case SIGUSR1:
  42                 if (pid <= 0) break;
  43                 memcpy(&last_sigterm_info, si, sizeof(*si));
  44
  45                 /** forward the sig to the child */
  46                 kill(pid, sig);
  47                 break;
  48         case SIGHUP: /** do a graceful restart */
  49                 if (pid <= 0) break;
  50                 memcpy(&last_sighup_info, si, sizeof(*si));
  51
  52                 /** do a graceful shutdown on the main process and start a new child */
  53                 kill(pid, SIGINT);
  54
  55                 usleep(5 * 1000); /** wait 5 microsec */
  56
  57                 start_process = 1;
  58                 break;
  59         case SIGCHLD:
  60                 /** a child died, de-combie it */
  61                 wait(&exitcode);
  62                 break;
  63         }
  64 }
  65
  66 int main(int argc, char **argv) {
  67         int is_shutdown = 0;
  68         struct sigaction act;
  69
  70         UNUSED(argc);
  71
  72         /**
  73          * we are running as root BEWARE
  74          */
  75
  76         memset(&act, 0, sizeof(act));
  77         act.sa_handler = SIG_IGN;
  78         sigaction(SIGPIPE, &act, NULL);
  79         sigaction(SIGUSR1, &act, NULL);
  80
  81         act.sa_sigaction = sigaction_handler;
  82         sigemptyset(&act.sa_mask);
  83         act.sa_flags = SA_SIGINFO;
  84
  85         sigaction(SIGINT,  &act, NULL);
  86         sigaction(SIGTERM, &act, NULL);
  87         sigaction(SIGUSR1, &act, NULL);
  88         sigaction(SIGHUP,  &act, NULL);
  89         sigaction(SIGALRM, &act, NULL);
  90         sigaction(SIGCHLD, &act, NULL);
  91
  92         /* check that the compiled in path has the right user,
  93          *
  94          * BEWARE: there is a race between the check here and the exec later
  95          */
  96
  97         while (!is_shutdown) {
  98                 int exitcode = 0;
  99
 100                 if (start_process) {
 101                         pid = fork();
 102
 103                         if (0 == pid) {
 104                                 /* i'm the child */
 105
 106                                 argv[0] = BINPATH;
 107
 108                                 execvp(BINPATH, argv);
 109
 110                                 exit(1);
 111                         } else if (-1 == pid) {
 112                                 /** error */
 113
 114                                 return -1;
 115                         }
 116
 117                         /* I'm the angel */
 118                         start_process = 0;
 119                 }
 120
 121                 if ((pid_t)-1 == waitpid(pid, &exitcode, 0)) {
 122                         switch (errno) {
 123                         case EINTR:
 124                                 /* someone sent a signal ...
 125                                  * do we have to shutdown or restart the process */
 126                                 break;
 127                         case ECHILD:
 128                                 /**
 129                                  * make sure we are not in a race between the signal handler
 130                                  * and the process restart */
 131                                 if (!start_process) is_shutdown = 1;
 132                                 break;
 133                         default:
 134                                 break;
 135                         }
 136                 } else {
 137                         /** process went away */
 138
 139                         if (WIFEXITED(exitcode)) {
 140                                 /** normal exit */
 141
 142                                 is_shutdown = 1;
 143
 144                                 fprintf(stderr, "%s.%d: child (pid=%d) exited normally with exitcode: %d\n",
 145                                                 __FILE__, __LINE__,
 146                                                 pid,
 147                                                 WEXITSTATUS(exitcode));
 148
 149                         } else if (WIFSIGNALED(exitcode)) {
 150                                 /** got a signal */
 151
 152                                 fprintf(stderr, "%s.%d: child (pid=%d) exited unexpectedly with signal %d, restarting\n",
 153                                                 __FILE__, __LINE__,
 154                                                 pid,
 155                                                 WTERMSIG(exitcode));
 156
 157                                 start_process = 1;
 158                         }
 159                 }
 160         }
 161
 162         return 0;
 163 }
 164