mdw@git.distorted.org.uk Git - mLib/blob - sel/sig.c

   1 /* -*-c-*-
   2  *
   3  * Signal handling
   4  *
   5  * (c) 1999 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the mLib utilities library.
  11  *
  12  * mLib is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * mLib is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with mLib; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include <errno.h>
  31 #include <signal.h>
  32 #include <stdio.h>
  33 #include <stdlib.h>
  34 #include <string.h>
  35
  36 #include <fcntl.h>
  37
  38 #include "alloc.h"
  39 #include "fdflags.h"
  40 #include "macros.h"
  41 #include "report.h"
  42 #include "sel.h"
  43 #include "sig.h"
  44
  45 /*----- Data structures ---------------------------------------------------*/
  46
  47 typedef struct sigstate {
  48   struct sigaction sa;
  49   sig *list;
  50 } sigstate;
  51
  52 /*----- Static variables --------------------------------------------------*/
  53
  54 static sel_file sigsel;
  55 static int sigfd;
  56 static sigstate *sigs;
  57 static sigset_t ss_all, ss_caught;
  58 static unsigned nsig;
  59
  60 /*----- Main code ---------------------------------------------------------*/
  61
  62 /* --- @sig_handler@ --- *
  63  *
  64  * Arguments:   @int n@ = signal number
  65  *
  66  * Returns:     ---
  67  *
  68  * Use:         Generic signal handler.  Writes a single byte to the
  69  *              signal pipe.  The byte contains the signal number.  Also
  70  *              sets the appropriate bit in @ss_caught@ to indicate which
  71  *              signals are pending.
  72  */
  73
  74 static void sig_handler(int n)
  75 {
  76   int e = errno;
  77   unsigned char sch = (unsigned char)n;
  78   sigprocmask(SIG_BLOCK, &ss_all, 0);
  79   sigaddset(&ss_caught, n);
  80   DISCARD(write(sigfd, &sch, 1));
  81   /* The system should reset the signal mask here. */
  82   errno = e;
  83 }
  84
  85 /* --- @sig_read@ --- *
  86  *
  87  * Arguments:   @int fd@ = file descriptor to read
  88  *              @unsigned mode@ = thing to do with descriptor
  89  *              @void *p@ = uninteresting argument
  90  *
  91  * Returns:     ---
  92  *
  93  * Use:         Dispatches signals to their handlers safely.
  94  */
  95
  96 static void sig_read(int fd, unsigned mode, void *p)
  97 {
  98   sigset_t ss;
  99
 100   /* --- Read the currently caught signals --- *
 101    *
 102    * Block signals while the mask is being copied.
 103    */
 104
 105   {
 106     sigset_t oss;
 107     unsigned char buf[256];
 108
 109     sigprocmask(SIG_BLOCK, &ss_all, &oss);
 110     ss = ss_caught;
 111     sigemptyset(&ss_caught);
 112     while (read(fd, buf, sizeof(buf)) > 0)
 113       /* Do nothing */;
 114     sigprocmask(SIG_SETMASK, &oss, 0);
 115   }
 116
 117   /* --- Process the caught signals --- */
 118
 119   {
 120     int i;
 121     for (i = 0; i < nsig; i++) {
 122       sig *s;
 123       if (!sigismember(&ss, i))
 124         continue;
 125       s = sigs[i].list;
 126       while (s) {
 127         sig *ss = s;
 128         s = s->next;
 129         ss->proc(i, ss->p);
 130       }
 131     }
 132   }
 133 }
 134
 135 /* --- @sig_add@ --- *
 136  *
 137  * Arguments:   @sig *s@ = pointer to signal handler block
 138  *              @int n@ = number of the signal
 139  *              @void (*proc)(int n, void *p)@ = signal handler function
 140  *              @void *p@ = argument to pass to handler
 141  *
 142  * Returns:     ---
 143  *
 144  * Use:         Adds a signal handler.
 145  */
 146
 147 void sig_add(sig *s, int n, void (*proc)(int /*n*/, void */*p*/), void *p)
 148 {
 149   sigstate *ss = &sigs[n];
 150
 151   /* --- Initialize the block --- */
 152
 153   s->proc = proc;
 154   s->p = p;
 155   s->sig = n;
 156   s->next = ss->list;
 157   s->prev = 0;
 158
 159   /* --- Engage a signal handler, maybe --- */
 160
 161   if (!ss->list) {
 162     struct sigaction sa;
 163     sa.sa_handler = sig_handler;
 164     sa.sa_flags = SA_NOCLDSTOP;
 165 #ifdef SA_RESTART
 166     sa.sa_flags |= SA_RESTART;
 167 #endif
 168     sigemptyset(&sa.sa_mask);
 169     sigaddset(&ss_all, n);
 170     sigaction(n, &sa, &ss->sa);
 171   }
 172
 173   /* --- Link the block into the list --- */
 174
 175   if (ss->list)
 176     ss->list->prev = s;
 177   ss->list = s;
 178 }
 179
 180 /* --- @sig_remove@ --- *
 181  *
 182  * Arguments:   @sig *s@ = pointer to signal handler block
 183  *
 184  * Returns:     ---
 185  *
 186  * Use:         Removes the signal handler from the list.
 187  */
 188
 189 void sig_remove(sig *s)
 190 {
 191   sigstate *ss = &sigs[s->sig];
 192
 193   /* --- Unlink the handler block --- */
 194
 195   if (s->next)
 196     s->next->prev = s->prev;
 197   if (s->prev)
 198     s->prev->next = s->next;
 199   else
 200     ss->list = s->next;
 201
 202   /* --- Maybe remove the handler --- */
 203
 204   if (!ss->list) {
 205     sigaction(s->sig, &ss->sa, 0);
 206     sigdelset(&ss_all, s->sig);
 207   }
 208 }
 209
 210 /* --- @sig_init@ --- *
 211  *
 212  * Arguments:   @sel_state *s@ = pointer to select state
 213  *
 214  * Returns:     ---
 215  *
 216  * Use:         Initializes the signal handling system ready for use.
 217  */
 218
 219 void sig_init(sel_state *s)
 220 {
 221   int fd[2];
 222
 223   /* --- Work out how many signals there are --- */
 224
 225   {
 226     sigset_t ss;
 227     unsigned min = 0, max = 0;
 228
 229     sigemptyset(&ss);
 230
 231     /* --- Get a good upper bound --- *
 232      *
 233      * Cap the search at 256.  I'll be sending signal numbers as bytes.
 234      */
 235
 236     nsig = 1;
 237     while (sigaddset(&ss, nsig) == 0) {
 238       if (nsig == 256)
 239         goto counted;
 240       nsig <<= 1;
 241     }
 242
 243     /* --- Now binary search until I find the actual limit --- */
 244
 245     min = nsig >> 1;
 246     max = nsig;
 247     for (;;) {
 248       nsig = (min + max) >> 1;
 249       if (nsig == min)
 250         break;
 251       if (sigaddset(&ss, nsig))
 252         max = nsig;
 253       else
 254         min = nsig;
 255     }
 256   counted:;
 257   }
 258
 259   /* --- Initialize the signal state table --- */
 260
 261   {
 262     unsigned i;
 263
 264     sigs = xmalloc(nsig * sizeof(*sigs));
 265     for (i = 0; i < nsig; i++)
 266       sigs[i].list = 0;
 267   }
 268
 269   /* --- Create the signal pipe --- */
 270
 271   if (pipe(fd))
 272     die(1, "couldn't create pipe for signal handling");
 273
 274   /* --- Set both ends to nonblocking and close-on-exec --- */
 275
 276   fdflags(fd[0], O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC);
 277   fdflags(fd[1], O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC);
 278
 279   /* --- Set everything up for the future --- */
 280
 281   sigfd = fd[1];
 282   sel_initfile(s, &sigsel, fd[0], SEL_READ, sig_read, 0);
 283   sel_addfile(&sigsel);
 284   sigemptyset(&ss_all);
 285   sigemptyset(&ss_caught);
 286 }
 287
 288 /*----- That's all, folks -------------------------------------------------*/