tools/virtiofsd/fuse_signals.c

   1 /*
   2  * FUSE: Filesystem in Userspace
   3  * Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>
   4  *
   5  * Utility functions for setting signal handlers.
   6  *
   7  * This program can be distributed under the terms of the GNU LGPLv2.
   8  * See the file COPYING.LIB
   9  */
  10
  11 #include "qemu/osdep.h"
  12 #include "fuse_i.h"
  13 #include "fuse_lowlevel.h"
  14
  15 #include <errno.h>
  16 #include <signal.h>
  17 #include <stdio.h>
  18 #include <stdlib.h>
  19 #include <string.h>
  20
  21 static struct fuse_session *fuse_instance;
  22
  23 static void exit_handler(int sig)
  24 {
  25     if (fuse_instance) {
  26         fuse_session_exit(fuse_instance);
  27         if (sig <= 0) {
  28             fuse_log(FUSE_LOG_ERR, "assertion error: signal value <= 0\n");
  29             abort();
  30         }
  31         fuse_instance->error = sig;
  32     }
  33 }
  34
  35 static void do_nothing(int sig)
  36 {
  37     (void)sig;
  38 }
  39
  40 static int set_one_signal_handler(int sig, void (*handler)(int), int remove)
  41 {
  42     struct sigaction sa;
  43     struct sigaction old_sa;
  44
  45     memset(&sa, 0, sizeof(struct sigaction));
  46     sa.sa_handler = remove ? SIG_DFL : handler;
  47     sigemptyset(&(sa.sa_mask));
  48     sa.sa_flags = 0;
  49
  50     if (sigaction(sig, NULL, &old_sa) == -1) {
  51         fuse_log(FUSE_LOG_ERR, "fuse: cannot get old signal handler: %s\n",
  52                  strerror(errno));
  53         return -1;
  54     }
  55
  56     if (old_sa.sa_handler == (remove ? handler : SIG_DFL) &&
  57         sigaction(sig, &sa, NULL) == -1) {
  58         fuse_log(FUSE_LOG_ERR, "fuse: cannot set signal handler: %s\n",
  59                  strerror(errno));
  60         return -1;
  61     }
  62     return 0;
  63 }
  64
  65 int fuse_set_signal_handlers(struct fuse_session *se)
  66 {
  67     /*
  68      * If we used SIG_IGN instead of the do_nothing function,
  69      * then we would be unable to tell if we set SIG_IGN (and
  70      * thus should reset to SIG_DFL in fuse_remove_signal_handlers)
  71      * or if it was already set to SIG_IGN (and should be left
  72      * untouched.
  73      */
  74     if (set_one_signal_handler(SIGHUP, exit_handler, 0) == -1 ||
  75         set_one_signal_handler(SIGINT, exit_handler, 0) == -1 ||
  76         set_one_signal_handler(SIGTERM, exit_handler, 0) == -1 ||
  77         set_one_signal_handler(SIGPIPE, do_nothing, 0) == -1) {
  78         return -1;
  79     }
  80
  81     fuse_instance = se;
  82     return 0;
  83 }
  84
  85 void fuse_remove_signal_handlers(struct fuse_session *se)
  86 {
  87     if (fuse_instance != se) {
  88         fuse_log(FUSE_LOG_ERR,
  89                  "fuse: fuse_remove_signal_handlers: unknown session\n");
  90     } else {
  91         fuse_instance = NULL;
  92     }
  93
  94     set_one_signal_handler(SIGHUP, exit_handler, 1);
  95     set_one_signal_handler(SIGINT, exit_handler, 1);
  96     set_one_signal_handler(SIGTERM, exit_handler, 1);
  97     set_one_signal_handler(SIGPIPE, do_nothing, 1);
  98 }