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, const struct timeval *tv_now,
 180                              uint64_t *now)
 181 {
 182     if (*nfds_io<1) {
 183         *nfds_io=1;
 184         return ERANGE;
 185     }
 186     *nfds_io=1;
 187     fds[0].fd=spr;
 188     fds[0].events=POLLIN;
 189     return 0;
 190 }
 191
 192 static afterpoll_fn signal_afterpoll;
 193 static void signal_afterpoll(void *st, struct pollfd *fds, int nfds,
 194                              const struct timeval *tv, uint64_t *now)
 195 {
 196     uint8_t buf[16];
 197     struct signotify *n;
 198     sigset_t todo,old;
 199
 200     if (nfds && (fds->revents & POLLIN)) {
 201         read(spr,buf,16); /* We don't actually care what we read; as
 202                              long as there was at least one byte
 203                              (which there was) we'll pick up the
 204                              signals in the pending set */
 205
 206         /* We reset 'pending' before processing any of the signals
 207            that were pending so that we don't miss any signals that
 208            are delivered partway-through processing (all we assume
 209            about signal notification routines is that they handle all
 210            the work available at their _start_ and only optionally any
 211            work that arrives part-way through their execution). */
 212         sigprocmask(SIG_SETMASK,&fullset,&old);
 213         todo=pending;
 214         sigemptyset(&pending);
 215         sigprocmask(SIG_SETMASK,&old,NULL);
 216
 217         for (n=sigs; n; n=n->next)
 218             if (sigismember(&todo,n->signum))
 219                 n->notify(n->cst,n->signum);
 220     }
 221 }
 222
 223 static void set_default_signals(void)
 224 {
 225     struct signotify *n;
 226     sigset_t done;
 227     struct sigaction sa;
 228
 229     sigemptyset(&done);
 230     for (n=sigs; n; n=n->next)
 231         if (!sigismember(&done,n->signum)) {
 232             sigaddset(&done,n->signum);
 233             sa.sa_handler=SIG_DFL;
 234             sa.sa_mask=emptyset;
 235             sa.sa_flags=0;
 236             sigaction(n->signum,&sa,NULL);
 237         }
 238 }
 239
 240 static void signal_handler(int signum)
 241 {
 242     int saved_errno;
 243     uint8_t thing=0;
 244     sigaddset(&pending,signum);
 245     /* XXX the write() may set errno, which can make the main program fail.
 246        However, signal handlers aren't allowed to modify anything which
 247        is not of type sig_atomic_t.  The world is broken. */
 248     /* I have decided to save and restore errno anyway; on most
 249        architectures on which secnet can run modifications to errno
 250        will be atomic, and it seems to be the lesser of the two
 251        evils. */
 252     saved_errno=errno;
 253     write(spw,&thing,1); /* We don't care if this fails (i.e. the pipe
 254                             is full) because the service routine will
 255                             spot the pending signal anyway */
 256     errno=saved_errno;
 257 }
 258
 259 static void register_signal_handler(struct signotify *s)
 260 {
 261     struct sigaction sa;
 262     int rv;
 263
 264     if (!signal_handling) return;
 265
 266     if (sigismember(&registered,s->signum)) return;
 267     sigaddset(&registered,s->signum);
 268
 269     sa.sa_handler=signal_handler;
 270     sa.sa_mask=fullset;
 271     sa.sa_flags=0;
 272     rv=sigaction(s->signum,&sa,NULL);
 273     if (rv!=0) {
 274         fatal_perror("register_signal_handler: sigaction(%d)",s->signum);
 275     }
 276 }
 277
 278 void request_signal_notification(int signum, signal_notify_fn *notify,
 279                                  void *cst)
 280 {
 281     struct signotify *s;
 282     sigset_t old;
 283
 284     s=safe_malloc(sizeof(*s),"request_signal_notification");
 285     s->signum=signum;
 286     s->notify=notify;
 287     s->cst=cst;
 288     s->next=sigs;
 289     sigprocmask(SIG_SETMASK,&fullset,&old);
 290     sigs=s;
 291     register_signal_handler(s);
 292     sigprocmask(SIG_SETMASK,&old,NULL);
 293 }
 294
 295 void start_signal_handling(void)
 296 {
 297     int p[2];
 298     struct signotify *i;
 299
 300     sigemptyset(&emptyset);
 301     sigfillset(&fullset);
 302     sigemptyset(&registered);
 303     sigemptyset(&pending);
 304
 305     if (pipe(p)!=0) {
 306         fatal_perror("start_signal_handling: pipe");
 307     }
 308     spw=p[1];
 309     spr=p[0];
 310     if (fcntl(spw, F_SETFL, fcntl(spw, F_GETFL)|O_NONBLOCK)==-1) {
 311         fatal_perror("start_signal_handling: fcntl(O_NONBLOCK)");
 312     }
 313
 314     register_for_poll(NULL,signal_beforepoll,signal_afterpoll,1,"signal");
 315     signal_handling=True;
 316
 317     /* Register signal handlers for all the signals we're interested in */
 318     for (i=sigs; i; i=i->next) {
 319         register_signal_handler(i);
 320     }
 321
 322     request_signal_notification(SIGCHLD,sigchld_handler,NULL);
 323 }