libs/libc/unistd/: Add a crippled version of daemon().

include/unistd.h

@@ -290,6 +290,7 @@ void    _exit(int status) noreturn_function;
 unsigned int sleep(unsigned int seconds);
 int     usleep(useconds_t usec);
 int     pause(void);
+int     daemon(int nochdir, int noclose);
 
 /* File descriptor operations */
 

libs/libc/unistd/Make.defs

@@ -35,7 +35,7 @@
 
 # Add the unistd C files to the build
 
-CSRCS += lib_access.c lib_swab.c lib_sysconf.c
+CSRCS += lib_access.c lib_daemon.c lib_swab.c lib_sysconf.c
 CSRCS += lib_getopt.c lib_getoptargp.c lib_getoptindp.c lib_getoptoptp.c
 
 ifneq ($(CONFIG_NFILE_DESCRIPTORS),0)

libs/libc/unistd/lib_daemon.c

@@ -0,0 +1,172 @@
+/****************************************************************************
+ * libs/libc/unistd/lib_daemon.c
+ *
+ *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+/* Not appropriate for use within the OS */
+
+#if defined(CONFIG_BUILD_FLAT) || !defined(__KERNEL__)
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: daemon
+ *
+ * Description:
+ *   The daemon() function is for programs wishing to detach themselves from
+ *   the controlling terminal and run in the background as system daemons.
+ *
+ *   NOTE: daemon() is a non-standard GNU C library interface (based on a
+ *   BSD interface of the same way which behaves slightly differently).
+ *   The interfaces defined at OpenGroup.org are the interfaces that govern
+ *   NuttX.  deamon() is only described in the Linux man pages like:\
+ *   http://man7.org/linux/man-pages/man3/daemon.3.html
+ *
+ * Limitations:
+ *   NuttX does not implement controlling terminals so the primary purpose
+ *   of this interface is not supported.  Additional operations controlled
+ *   by input parameters are supported, however.
+ *
+ *   It is not possible to support a true Linux daemon() helper function
+ *   because it is designed to work only in the Linux environment and cannot
+ *   be translated to NuttX.  The above mentioned web page states:
+ *
+ *     (This function forks, and if the fork(2) succeeds, the parent calls
+ *     _exit(2), so that further errors are seen by the child only.)  On
+ *
+ *   So the basic operation of the NuttX daemon() is different.  The GNU C
+ *   library daemon() begins will logic like:
+ *
+ *     switch (fork())
+ *       {
+ *         case -1:
+ *           return -1;
+ *         case 0:
+ *           break;
+ *         default:
+ *           exit(0);
+ *       }
+ *
+ *    This implementation begins essentially 'pretending' that we forked
+ *    and that the fork was successful and that we are the child of the
+ *    vim fork.
+ *
+ * Input Parameters:
+ *   nochdir - If nochdir is zero, daemon() changes the process's current
+ *     working directory to the root directory ("/"); otherwise, the current
+ *     working  directory is left unchanged.
+ *   noclose - If noclose is zero, daemon() redirects standard input,
+ *     standard output and standard error to /dev/null; otherwise, no changes
+ *     are made to these file descriptors.
+ *
+ * Returned Value:
+ *   0 is returned on success; otherwise, -1 is returned with errno set
+ *   appropriately.
+ *
+ ****************************************************************************/
+
+int daemon(int nochdir, int noclose)
+{
+#ifndef CONFIG_DISABLE_ENVIRON
+  if (nochdir == 0)
+    {
+      int ret = chdir("/");
+      if (ret < 0)
+        {
+          return -1;  /* chdir() will set the errno variable */
+        }
+    }
+#endif
+
+#if CONFIG_NFILE_DESCRIPTORS > 0
+  if (noclose == 0)
+    {
+      int fd = open("/dev/null", O_RDWR);
+      if (fd < 0)
+        {
+          return -1;
+        }
+
+      /* Make sure the stdin, stdout, and stderr are closed */
+
+      (void)fclose(stdin);
+      (void)fclose(stdout);
+      (void)fclose(stderr);
+
+      /* Dup the fd to create standard fd 0-2 */
+
+      (void)dup2(fd, 0);
+      (void)dup2(fd, 1);
+      (void)dup2(fd, 2);
+
+      /* fdopen to get the stdin, stdout and stderr streams. The
+       * following logic depends on the fact that the library layer
+       * will allocate FILEs in order.  And since we closed stdin,
+       * stdout, and stderr above, that is what we should get.
+       *
+       * fd = 0 is stdin  (read-only)
+       * fd = 1 is stdout (write-only, append)
+       * fd = 2 is stderr (write-only, append)
+       */
+
+      (void)fdopen(0, "r");
+      (void)fdopen(1, "a");
+      (void)fdopen(2, "a");
+
+      /* We can close the original file descriptor now (unless it was
+       * one of* 0-2)
+       */
+
+      if (fd > 2)
+       {
+         (void)close(fd);
+       }
+    }
+#endif
+
+  return OK;
+}
+
+#endif /* CONFIG_BUILD_FLAT=y || !__KERNEL__ */