exec.c

   1 /*
   2  * Copyright (C) 2003-2008 Andre Noll <maan@systemlinux.org>
   3  *
   4  * Licensed under the GPL v2. For licencing details see COPYING.
   5  */
   6
   7 /** \file exec.c Helper functions for spawning new processes. */
   8 #include <dirent.h>
   9 #include "para.h"
  10 #include "close_on_fork.h"
  11 #include "error.h"
  12 #include "string.h"
  13 #include "fd.h"
  14
  15 /**
  16  * Spawn a new process and redirect fd 0, 1, and 2.
  17  *
  18  * \param pid Will hold the pid of the created process upon return.
  19  * \param file Path of the executable to execute.
  20  * \param args The argument array for the command.
  21  * \param fds a Pointer to a value-result array.
  22  *
  23  * \return Standard.
  24  *
  25  * \sa null(4), pipe(2), dup2(2), fork(2), exec(3).
  26  */
  27 static int para_exec(pid_t *pid, const char *file, char *const *const args, int *fds)
  28 {
  29         int ret, in[2] = {-1, -1}, out[2] = {-1, -1}, err[2] = {-1, -1},
  30                 null = -1; /* ;) */
  31
  32         ret = -E_DUP_PIPE;
  33         if (fds[0] > 0 && pipe(in) < 0)
  34                 goto err_out;
  35         if (fds[1] > 0 && pipe(out) < 0)
  36                 goto err_out;
  37         if (fds[2] > 0 && pipe(err) < 0)
  38                 goto err_out;
  39         if (!fds[0] || !fds[1] || !fds[2]) {
  40                 ret = para_open("/dev/null", O_RDONLY, 42);
  41                 if (ret < 0)
  42                         goto err_out;
  43                 null = ret;
  44         }
  45         ret = fork();
  46         if (ret < 0) {
  47                 ret = -ERRNO_TO_PARA_ERROR(errno);
  48                 goto err_out;
  49         }
  50         *pid = ret;
  51         if (!(*pid)) { /* child */
  52                 close_listed_fds(); /* close unneeded fds */
  53                 if (fds[0] >= 0) {
  54                         if (fds[0]) {
  55                                 close(in[1]);
  56                                 if (in[0] != STDIN_FILENO)
  57                                         dup2(in[0], STDIN_FILENO);
  58                         } else
  59                                 dup2(null, STDIN_FILENO);
  60                 }
  61                 if (fds[1] >= 0) {
  62                         if (fds[1]) {
  63                                 close(out[0]);
  64                                 if (out[1] != STDOUT_FILENO)
  65                                         dup2(out[1], STDOUT_FILENO);
  66                         } else
  67                                 dup2(null, STDOUT_FILENO);
  68                 }
  69                 if (fds[2] >= 0) {
  70                         if (fds[2]) {
  71                                 close(err[0]);
  72                                 if (err[1] != STDERR_FILENO)
  73                                         dup2(err[1], STDERR_FILENO);
  74                         } else
  75                                 dup2(null, STDERR_FILENO);
  76                 }
  77                 if (null >= 0)
  78                         close(null);
  79                 execvp(file, args);
  80                 _exit(EXIT_FAILURE);
  81         }
  82         if (fds[0] > 0) {
  83                 close(in[0]);
  84                 *fds = in[1];
  85         }
  86         if (fds[1] > 0) {
  87                 close(out[1]);
  88                 *(fds + 1) = out[0];
  89         }
  90         if (fds[2] > 0) {
  91                 close(err[1]);
  92                 *(fds + 2) = err[0];
  93         }
  94         if (null >= 0)
  95                 close(null);
  96         return 1;
  97 err_out:
  98         if (err[0] >= 0)
  99                 close(err[0]);
 100         if (err[1] >= 0)
 101                 close(err[1]);
 102         if (out[0] >= 0)
 103                 close(out[0]);
 104         if (out[1] >= 0)
 105                 close(out[1]);
 106         if (in[0] >= 0)
 107                 close(in[0]);
 108         if (in[1] >= 0)
 109                 close(in[1]);
 110         if (null >= 0)
 111                 close(null);
 112         PARA_ERROR_LOG("%s\n", para_strerror(-ret));
 113         return ret;
 114 }
 115
 116 /**
 117  * Exec the given command.
 118  *
 119  * \param pid Will hold the pid of the created process upon return.
 120  * \param cmdline Holds the command and its arguments, seperated by spaces.
 121  * \param fds A pointer to a value-result array.
 122  *
 123  * This function uses fork/exec to create a new process. \a fds must be a
 124  * pointer to three integers, corresponding to stdin, stdout and stderr
 125  * respectively. It specifies how to deal with fd 0, 1, 2 in the child. The
 126  * contents of \a fds are interpreted as follows:
 127  *
 128  *      - fd[i] < 0: leave fd \a i alone.
 129  *      - fd[i] = 0: dup fd \a i to \p /dev/null.
 130  *      - fd[i] > 0: create a pipe and dup i to one end of that pipe.
 131  *      Upon return, fd[i] contains the file descriptor of the pipe.
 132  *
 133  *      In any case, all unneeded filedescriptors are closed.
 134  *
 135  * \return Standard.
 136  */
 137 int para_exec_cmdline_pid(pid_t *pid, const char *cmdline, int *fds)
 138 {
 139         int argc, ret;
 140         char **argv;
 141         char *tmp = para_strdup(cmdline);
 142
 143         if (!tmp)
 144                 exit(EXIT_FAILURE);
 145         argc = split_args(tmp, &argv, " \t");
 146         ret = para_exec(pid, argv[0], argv, fds);
 147         free(argv);
 148         free(tmp);
 149         return ret;
 150 }