utils/wvfork.cc

   1 /*
   2  * Worldvisions Weaver Software:
   3  *   Copyright (C) 1997-2002 Net Integration Technologies, Inc.
   4  *
   5  * wvfork() just runs fork(), but it closes all file descriptors that
   6  * are flagged close-on-exec, since we don't necessarily always run
   7  * exec() after we fork()...
   8  *
   9  * This fixes the year-old mystery bug where WvTapeBackup caused
  10  * watchdog reboots because the CHILD process wasn't touching it, and
  11  * it was already open before the fork()...
  12  *
  13  * If you want to explicitly leave a file descriptor OPEN, even if
  14  * it's marked close-on-exec, then add the fd number to dontclose, and
  15  * pass that to wvfork().  This is mainly useful for WvLoopbacks --
  16  * you may want certain ones open or closed depending on which call to
  17  * wvfork() you're making.  (for WvTapeBackup, you want the three
  18  * backup loopbacks open, and, say, any WvResolver loopbacks closed.)
  19  */
  20 #include <fcntl.h>
  21
  22 #include "wvfork.h"
  23 #include "wvlinklist.h"
  24
  25 #define MAX_FD sysconf(_SC_OPEN_MAX) + 1
  26
  27 DeclareWvList(WvForkCallback);
  28 static WvForkCallbackList *callbacks;
  29
  30 class StupidWvForkDeallocator
  31 {
  32 public:
  33     ~StupidWvForkDeallocator()
  34         { if (callbacks) delete callbacks; }
  35 };
  36
  37 static StupidWvForkDeallocator sfd;
  38
  39
  40 // note: this shouldn't really be needed (it would be better to use a simple
  41 // static list), but might be needed if your dynamic linker (ld.so) runs
  42 // global constructors in the wrong order.
  43 static WvForkCallbackList &get_callbacks()
  44 {
  45     if (!callbacks)
  46         callbacks = new WvForkCallbackList;
  47     return *callbacks;
  48 }
  49
  50
  51 void add_wvfork_callback(WvForkCallback cb)
  52 {
  53 #if 0
  54     // be sure we don't add this twice
  55     WvForkCallbackList::Iter i(get_callbacks());
  56     for (i.rewind(); i.next(); )
  57         if (*i == cb) return;
  58 #endif
  59     get_callbacks().append(new WvForkCallback(cb), true);
  60 }
  61
  62 #if 0
  63 void remove_wvfork_callback(WvForkCallback cb)
  64 {
  65     WvForkCallbackList::Iter i(get_callbacks());
  66     for (i.rewind(); i.next(); )
  67         if (*i == cb) i.xunlink();
  68 }
  69 #endif
  70
  71 pid_t wvfork(int dontclose1, int dontclose2)
  72 {
  73     intTable t(1);
  74     if (dontclose1 >= 0)
  75         t.add(&dontclose1, false);
  76     if (dontclose2 >= 0)
  77         t.add(&dontclose2, false);
  78     return (wvfork(t));
  79 }
  80
  81 pid_t wvfork_start(int *waitfd)
  82 {
  83     int waitpipe[2];
  84
  85     if (pipe(waitpipe) < 0)
  86         return -1;
  87
  88     pid_t pid = fork();
  89
  90     WvForkCallbackList::Iter i(get_callbacks());
  91     for (i.rewind(); i.next(); )
  92     {
  93         WvForkCallback *cb = i.ptr();
  94         (*cb)(pid);
  95     }
  96
  97     if (pid < 0)
  98         return pid;
  99     else if (pid > 0)
 100     {
 101         // parent process. close its writing end of the pipe and wait
 102         // for its reading end to close.
 103         char buf;
 104         close(waitpipe[1]);
 105         read(waitpipe[0], &buf, 1);
 106         close(waitpipe[0]);
 107     }
 108     else
 109     {
 110         // child process. close its reading end of the pipe.
 111         close(waitpipe[0]);
 112         *waitfd = waitpipe[1];
 113     }
 114
 115     return pid;
 116 }
 117
 118 pid_t wvfork(intTable &dontclose)
 119 {
 120     int waitfd = -1;
 121     pid_t pid = wvfork_start(&waitfd);
 122
 123     if (pid != 0)
 124     {
 125         // parent or error
 126         return pid;
 127     }
 128
 129     // child process
 130     // check the close-on-exec flag of all file descriptors
 131     for (int fd = 0; fd < MAX_FD; fd++)
 132     {
 133         if (!dontclose[fd] && fd != waitfd &&
 134             (fcntl(fd, F_GETFD) & FD_CLOEXEC) > 0)
 135             close(fd);
 136     }
 137
 138     close(waitfd);
 139
 140     return pid;
 141 }