mdw@git.distorted.org.uk Git - secnet/blob - process.c

   1 #include "secnet.h"
   2 #include <unistd.h>
   3 #include <fcntl.h>
   4 #include <errno.h>
   5 #include <sys/wait.h>
   6 #include "process.h"
   7
   8 /* Advice about children from Peter:
   9 Better way: before the fork, make a pipe. In the child close the
  10 +reading end. Make the writing end close-on-exec. If the dup2 or exec fails,
  11 +write the errno value. In the parent, close the writing end. Now you can read
  12 +from it. If you get an errno value from the pipe, the process failed and you
  13 +know why. If you get EOF, the exec succeeded.
  14
  15 <Senji> So, close on exec only closes if exec isn't going to return then?
  16 <Diziet> qu: I wouldn't bother with all that with pipes.  Remember that the
  17 +runtime system can still make exec fail when it's `too late'.
  18 <Senji> Diz - I would rather have a coherant error message than 'child failed'
  19 <Diziet> The child, if it fails to exec, should print a message to stderr
  20 +(giving errno and what it was trying to execute, most likely), and exit
  21 +nonzero.
  22 <Diziet> It should exit calling _exit.
  23 */
  24
  25 /* Process handling - subprocesses, signals, etc. */
  26
  27 static bool_t signal_handling=False;
  28 static sigset_t emptyset, fullset;
  29 static sigset_t registered,pending;
  30
  31 struct child {
  32     pid_t pid;
  33     cstring_t desc;
  34     process_callback_fn *cb;
  35     void *cst;
  36     bool_t finished;
  37     struct child *next;
  38 };
  39
  40 static struct child *children=NULL;
  41
  42 struct signotify {
  43     int signum;
  44     signal_notify_fn *notify;
  45     void *cst;
  46     struct signotify *next;
  47 };
  48
  49 static struct signotify *sigs=NULL;
  50
  51 static int spw,spr; /* file descriptors for signal notification pipe */
  52
  53 static void set_default_signals(void);
  54
  55 /* Long-lived subprocesses can only be started once we've started
  56    signal processing so that we can catch SIGCHLD for them and report
  57    their exit status using the callback function.  We block SIGCHLD
  58    until signal processing has begun. */
  59 pid_t makesubproc(process_entry_fn *entry, process_callback_fn *cb,
  60                  void *est, void *cst, cstring_t desc)
  61 {
  62     struct child *c;
  63     pid_t p;
  64
  65     c=safe_malloc(sizeof(*c),"makesubproc");
  66     c->desc=desc;
  67     c->cb=cb;
  68     c->cst=cst;
  69
  70     if (!signal_handling) {
  71         fatal("makesubproc called before signal handling started");
  72     }
  73     p=fork();
  74     if (p==0) {
  75         /* Child process */
  76         set_default_signals();
  77         sigprocmask(SIG_SETMASK,&emptyset,NULL);
  78         entry(est);
  79         abort();
  80     } else if (p==-1) {
  81         fatal_perror("makesubproc (%s): fork",desc);
  82     }
  83     c->pid=p;
  84     c->finished=False;
  85     c->next=children;
  86     children=c;
  87     return p;
  88 }
  89
  90 static signal_notify_fn sigchld_handler;
  91 static void sigchld_handler(void *st, int signum)
  92 {
  93     struct child *i,*n,**p;
  94     struct work {
  95         pid_t pid;
  96         process_callback_fn *cb;
  97         void *cst;
  98         int status;
  99         struct work *next;
 100     };
 101     struct work *w=NULL, *nw;
 102     pid_t rv;
 103     int status;
 104
 105     for (i=children; i; i=i->next) {
 106         rv=waitpid(i->pid,&status,WNOHANG);
 107         if (rv==-1) {
 108             fatal_perror("sigchld_handler: waitpid");
 109         }
 110         if (rv==i->pid) {
 111             i->finished=True;
 112
 113             nw=safe_malloc(sizeof(*nw),"sigchld_handler");
 114             nw->pid=i->pid;
 115             nw->cb=i->cb;
 116             nw->cst=i->cst;
 117             nw->status=status;
 118             nw->next=w;
 119             w=nw;
 120         }
 121     }
 122
 123     /* Remove all the finished tasks from the list of children */
 124     for (i=children, p=&children; i; i=n) {
 125         n=i->next;
 126         if (i->finished) {
 127             free(i);
 128             *p=n;
 129         } else {
 130             p=&i->next;
 131         }
 132     }
 133
 134     /* Notify as appropriate, then free the list */
 135     while (w) {
 136         w->cb(w->cst,w->pid,w->status);
 137         nw=w;
 138         w=w->next;
 139         free(nw);
 140     }
 141 }
 142
 143 int sys_cmd(const char *path, const char *arg, ...)
 144 {
 145     va_list ap;
 146     int rv;
 147     pid_t c;
 148
 149     va_start(ap,arg);
 150     c=fork();
 151     if (c) {
 152         /* Parent -> wait for child */
 153         waitpid(c,&rv,0);
 154     } else if (c==0) {
 155         char *args[100];
 156         int i;
 157         /* Child -> exec command */
 158         /* Really we ought to strcpy() the arguments into the args array,
 159            since the arguments are const char *.  Since we'll exit anyway
 160            if the execvp() fails this seems somewhat pointless, and
 161            increases the chance of the child process failing before it
 162            gets to exec(). */
 163         args[0]=(char *)arg;
 164         i=1;
 165         while ((args[i++]=va_arg(ap,char *)));
 166         execvp(path,args);
 167         exit(1);
 168     } else {
 169         /* Error */
 170         fatal_perror("sys_cmd(%s,%s,...)");
 171     }
 172
 173     va_end(ap);
 174     return rv;
 175 }
 176
 177 static beforepoll_fn signal_beforepoll;
 178 static int signal_beforepoll(void *st, struct pollfd *fds, int *nfds_io,
 179                              int *timeout_io)
 180 {
 181     if (*nfds_io<1) {
 182         *nfds_io=1;
 183         return ERANGE;
 184     }
 185     *nfds_io=1;
 186     fds[0].fd=spr;
 187     fds[0].events=POLLIN;
 188     return 0;
 189 }
 190
 191 static afterpoll_fn signal_afterpoll;
 192 static void signal_afterpoll(void *st, struct pollfd *fds, int nfds)
 193 {
 194     uint8_t buf[16];
 195     struct signotify *n;
 196     sigset_t todo,old;
 197
 198     if (nfds && (fds->revents & POLLIN)) {
 199         read(spr,buf,16); /* We don't actually care what we read; as
 200                              long as there was at least one byte
 201                              (which there was) we'll pick up the
 202                              signals in the pending set */
 203
 204         /* We reset 'pending' before processing any of the signals
 205            that were pending so that we don't miss any signals that
 206            are delivered partway-through processing (all we assume
 207            about signal notification routines is that they handle all
 208            the work available at their _start_ and only optionally any
 209            work that arrives part-way through their execution). */
 210         sigprocmask(SIG_SETMASK,&fullset,&old);
 211         todo=pending;
 212         sigemptyset(&pending);
 213         sigprocmask(SIG_SETMASK,&old,NULL);
 214
 215         for (n=sigs; n; n=n->next)
 216             if (sigismember(&todo,n->signum))
 217                 n->notify(n->cst,n->signum);
 218     }
 219 }
 220
 221 static void set_default_signals(void)
 222 {
 223     struct signotify *n;
 224     sigset_t done;
 225     struct sigaction sa;
 226
 227     sigemptyset(&done);
 228     for (n=sigs; n; n=n->next)
 229         if (!sigismember(&done,n->signum)) {
 230             sigaddset(&done,n->signum);
 231             sa.sa_handler=SIG_DFL;
 232             sa.sa_mask=emptyset;
 233             sa.sa_flags=0;
 234             sigaction(n->signum,&sa,NULL);
 235         }
 236 }
 237
 238 static void signal_handler(int signum)
 239 {
 240     int saved_errno;
 241     uint8_t thing=0;
 242     sigaddset(&pending,signum);
 243     /* XXX the write() may set errno, which can make the main program fail.
 244        However, signal handlers aren't allowed to modify anything which
 245        is not of type sig_atomic_t.  The world is broken. */
 246     /* I have decided to save and restore errno anyway; on most
 247        architectures on which secnet can run modifications to errno
 248        will be atomic, and it seems to be the lesser of the two
 249        evils. */
 250     saved_errno=errno;
 251     write(spw,&thing,1); /* We don't care if this fails (i.e. the pipe
 252                             is full) because the service routine will
 253                             spot the pending signal anyway */
 254     errno=saved_errno;
 255 }
 256
 257 static void register_signal_handler(struct signotify *s)
 258 {
 259     struct sigaction sa;
 260     int rv;
 261
 262     if (!signal_handling) return;
 263
 264     if (sigismember(&registered,s->signum)) return;
 265     sigaddset(&registered,s->signum);
 266
 267     sa.sa_handler=signal_handler;
 268     sa.sa_mask=fullset;
 269     sa.sa_flags=0;
 270     rv=sigaction(s->signum,&sa,NULL);
 271     if (rv!=0) {
 272         fatal_perror("register_signal_handler: sigaction(%d)",s->signum);
 273     }
 274 }
 275
 276 void request_signal_notification(int signum, signal_notify_fn *notify,
 277                                  void *cst)
 278 {
 279     struct signotify *s;
 280     sigset_t old;
 281
 282     s=safe_malloc(sizeof(*s),"request_signal_notification");
 283     s->signum=signum;
 284     s->notify=notify;
 285     s->cst=cst;
 286     s->next=sigs;
 287     sigprocmask(SIG_SETMASK,&fullset,&old);
 288     sigs=s;
 289     register_signal_handler(s);
 290     sigprocmask(SIG_SETMASK,&old,NULL);
 291 }
 292
 293 void start_signal_handling(void)
 294 {
 295     int p[2];
 296     struct signotify *i;
 297
 298     sigemptyset(&emptyset);
 299     sigfillset(&fullset);
 300     sigemptyset(&registered);
 301     sigemptyset(&pending);
 302
 303     if (pipe(p)!=0) {
 304         fatal_perror("start_signal_handling: pipe");
 305     }
 306     spw=p[1];
 307     spr=p[0];
 308     if (fcntl(spw, F_SETFL, fcntl(spw, F_GETFL)|O_NONBLOCK)==-1) {
 309         fatal_perror("start_signal_handling: fcntl(O_NONBLOCK)");
 310     }
 311
 312     register_for_poll(NULL,signal_beforepoll,signal_afterpoll,1,"signal");
 313     signal_handling=True;
 314
 315     /* Register signal handlers for all the signals we're interested in */
 316     for (i=sigs; i; i=i->next) {
 317         register_signal_handler(i);
 318     }
 319
 320     request_signal_notification(SIGCHLD,sigchld_handler,NULL);
 321 }