add daemon

Signed-off-by: Mattias Andrée <maandree@member.fsf.org>

1 files changed, 99 insertions, 0 deletions

diff --git a/src/unistd/daemon.c b/src/unistd/daemon.c
new file mode 100644
index 0000000..5d7c34d
--- /dev/null
+++ b/src/unistd/daemon.c
@@ -0,0 +1,99 @@
+/**
+ * slibc — Yet another C library
+ * Copyright © 2015  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <unistd.h>
+#include <fcntl.h>
+
+
+
+/**
+ * Detach the process from the controlling terminal
+ * and run in the background.
+ * 
+ * The function shall change the working directory
+ * to '/' to avoid block a mountpoint from being
+ * unmounted. It shall also change direct stdin,
+ * stdout, and stderr to '/dev/null'. It shall
+ * then double-fork, and between the fork, become
+ * a session leader, temporarily, so that the
+ * it no longer has a controlling terminal.
+ * 
+ * Note well, this function does not implement a
+ * reliable or particularly correct mechanism for
+ * daemonising a process. It shall not be used!
+ * Note, the GNU implementation is slightly
+ * different because of a bug.
+ * 
+ * @param   nochdir  The not change working directory to '/'.
+ * @param   noclose  The not redirect stdin, stdout, and stderr to '/dev/null'.
+ * @return           Zero on success, -1 on error.
+ * 
+ * @throws  EACCES  If `nochdir` is zero, and the user is denied access to '/'.
+ * @throws          Any error specified for open(3).
+ * @throws          Any error specified for dup2(3).
+ * @throws          Any error specified for fork(3).
+ * @throws          Any error specified for setsid(3).
+ * 
+ * @since  Always.
+ */
+int daemon(int nochdir, int noclose)
+{
+  int fd = -1;
+  int saved_errno;
+  
+  if (nochdir ? 0 : chdir("/"))
+    return -1;
+  
+  if (noclose == 0)
+    {
+      if (fd = open("/dev/null", O_RDWR), fd < 0)
+	return -1;
+      
+      if (dup2(fd, 0) < 0)  goto fail;
+      if (dup2(fd, 1) < 0)  goto fail;
+      if (dup2(fd, 2) < 0)  goto fail;
+      
+      if (fd > 2)
+	close(fd);
+    }
+  
+  switch (fork())
+    {
+    case  0:  break;
+    case -1:  return -1;
+    default:  _exit(0);
+    }
+
+  if (setsid() < 0)
+    return -1;
+
+  switch (fork())
+    {
+    case  0:  break;
+    case -1:  return -1;
+    default:  _exit(0);
+    }
+  
+  return 0;
+ fail:
+  saved_errno = errno;
+  if (fd > 2)
+    close (fd);
+  errno = saved_errno;
+  return -1;
+}
+