mdw@git.distorted.org.uk Git - distorted-chroot/blob - src/jobclient.c

   1 /* -*-c-*-
   2  *
   3  * Job client low-level magic
   4  *
   5  * (c) 2019 Mark Wooding
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the distorted.org.uk chroot maintenance tools.
  11  *
  12  * distorted-chroot is free software: you can redistribute it and/or
  13  * modify it under the terms of the GNU 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  * distorted-chroot 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 GNU
  20  * General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with distorted-chroot.  If not, write to the Free Software
  24  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  25  * USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include <assert.h>
  31 #include <errno.h>
  32 #include <signal.h>
  33
  34 #include <sys/types.h>
  35 #include <sys/wait.h>
  36 #include <unistd.h>
  37
  38 #define PY_SSIZE_T_CLEAN
  39 #include <Python.h>
  40
  41 /*----- Static variables --------------------------------------------------*/
  42
  43 static volatile int sigfd = -1;
  44
  45 /*----- Main code ---------------------------------------------------------*/
  46
  47 static void chld(int sig)
  48   { int fd = sigfd; if (fd != -1) { close(fd); sigfd = -1; } }
  49
  50 static PyObject *pymeth_jobclient(PyObject *me, PyObject *arg)
  51 {
  52   PyObject *rc = 0;
  53   struct sigaction sa, oldsa;
  54   sigset_t mask, oldmask;
  55   int rstrchld = 0;
  56   int fd, sfd;
  57   int kid, st;
  58   ssize_t n;
  59   char ch;
  60
  61   /* Parse the arguments. */
  62   if (!PyArg_ParseTuple(arg, "i", &fd)) goto end;
  63
  64   /* Prepare to be able to block `SIGCHLD'. */
  65   sigemptyset(&mask); sigaddset(&mask, SIGCHLD);
  66   if (sigprocmask(SIG_SETMASK, 0, &oldmask)) goto oserr;
  67
  68   /* Establish the signal handler. */
  69   sa.sa_handler = chld;
  70   sigemptyset(&sa.sa_mask); sigaddset(&sa.sa_mask, SIGCHLD);
  71   sa.sa_flags = SA_NOCLDSTOP;
  72   if (sigaction(SIGCHLD, &sa, &oldsa)) goto oserr;
  73   rstrchld = 1;
  74
  75   /* Establish a copy of the file descriptor.  If a signal occurs, we'll
  76    * clobber this descriptor: see below.  If we come back here, we'll
  77    * probably need to reinstate this, but check just in case: we don't want a
  78    * descriptor leak.
  79    */
  80 again:
  81   if (sigprocmask(SIG_BLOCK, &mask, 0)) goto oserr;
  82   sfd = sigfd;
  83   if (sfd == -1) {
  84     sfd = dup(fd); if (sfd == -1) goto oserr;
  85     sigfd = sfd;
  86   }
  87   if (sigprocmask(SIG_UNBLOCK, &mask, 0)) goto oserr;
  88
  89   /* Check for child processes.  If a child exit somehow failed to be
  90    * spotted earlier, this is our chance to notice and do something about it.
  91    */
  92   kid = waitpid(-1, &st, WNOHANG);
  93   if (kid == -1 && errno != ECHILD) goto oserr;
  94   else if (kid > 0)
  95     { rc = Py_BuildValue("(Oii)", Py_None, kid, st); goto end; }
  96
  97   /* Read from the pipe.  If a child exits between the `waitpid' above and
  98    * the `read' here, the signal handler will pop and close the descriptor,
  99    * so `read' will report `EBADF'.  If a child exits while we're waiting for
 100    * a byte on the descriptor, then `read' will report `EINTR'.  If anything
 101    * like this happens, then we go back and try reaping children again.
 102    */
 103   Py_BEGIN_ALLOW_THREADS
 104   n = read(sigfd, &ch, 1);
 105   Py_END_ALLOW_THREADS
 106   if (n == 1) rc = Py_BuildValue("(cOO)", ch, Py_None, Py_None);
 107   else if (!n) rc = Py_BuildValue("(sOO)", "", Py_None, Py_None);
 108   else if (n != -1) {
 109     PyErr_SetString(PyExc_SystemError, "impossible return from read");
 110     goto end;
 111   } else if (errno == EINTR || errno == EBADF) goto again;
 112   else goto oserr;
 113
 114   /* We're done. */
 115   goto end;
 116
 117 oserr:
 118   /* Report a system error. */
 119   PyErr_SetFromErrnoWithFilename(PyExc_OSError, 0); goto end;
 120
 121 end:
 122   /* Clean up and return. */
 123   if (rstrchld) {
 124     sigprocmask(SIG_SETMASK, &oldmask, 0);
 125     sigaction(SIGCHLD, &oldsa, 0);
 126   }
 127   sfd = sigfd; if (sfd != -1) { close(sfd); sigfd = -1; }
 128   return (rc);
 129 }
 130
 131 static PyMethodDef methods[] = {
 132   { "jobclient", pymeth_jobclient, METH_VARARGS,
 133     "jobclient(FD) -> (TOKEN, PID, STATUS)" },
 134   { 0 }
 135 };
 136
 137 PyMODINIT_FUNC initjobclient(void)
 138   { Py_InitModule("jobclient", methods); }
 139
 140 /*----- That's all, folks -------------------------------------------------*/