daemonize: clean up code

This was originally based on some other code but its mostly misleading
comments now. Massively clean this up and accept its now a total fork.
There are no funciton changes here, just cleanup.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 14 insertions, 134 deletions

diff --git a/lib/bb/daemonize.py b/lib/bb/daemonize.py
index a4664ad76..a5a9d868d 100644
--- a/lib/bb/daemonize.py
+++ b/lib/bb/daemonize.py
@@ -1,51 +1,15 @@
 """
 Python Daemonizing helper
 
-Configurable daemon behaviors:
-
-    1.) The current working directory set to the "/" directory.
-    2.) The current file creation mode mask set to 0.
-    3.) Close all open files (1024). 
-    4.) Redirect standard I/O streams to "/dev/null".
-
-A failed call to fork() now raises an exception.
-
-References:
-    1) Advanced Programming in the Unix Environment: W. Richard Stevens
-	http://www.apuebook.com/apue3e.html
-    2) The Linux Programming Interface: Michael Kerrisk
-	http://man7.org/tlpi/index.html
-    3) Unix Programming Frequently Asked Questions:
-	http://www.faqs.org/faqs/unix-faq/programmer/faq/
-
-Modified to allow a function to be daemonized and return for 
-bitbake use by Richard Purdie
+Originally based on code Copyright (C) 2005 Chad J. Schroeder but now heavily modified
+to allow a function to be daemonized and return for bitbake use by Richard Purdie
 """
 
-__author__ = "Chad J. Schroeder"
-__copyright__ = "Copyright (C) 2005 Chad J. Schroeder"
-__version__ = "0.2"
-
-# Standard Python modules.
-import os                    # Miscellaneous OS interfaces.
-import sys                   # System-specific parameters and functions.
+import os
+import sys
 import io
 import traceback
 
-# Default daemon parameters.
-# File mode creation mask of the daemon.
-# For BitBake's children, we do want to inherit the parent umask.
-UMASK = None
-
-# Default maximum for the number of available file descriptors.
-MAXFD = 1024
-
-# The standard I/O file descriptors are redirected to /dev/null by default.
-if (hasattr(os, "devnull")):
-    REDIRECT_TO = os.devnull
-else:
-    REDIRECT_TO = "/dev/null"
-
 def createDaemon(function, logfile):
     """
     Detach a process from the controlling terminal and run it in the
@@ -67,36 +31,6 @@ def createDaemon(function, logfile):
         # leader of the new process group, we call os.setsid().  The process is
         # also guaranteed not to have a controlling terminal.
         os.setsid()
-
-        # Is ignoring SIGHUP necessary?
-        #
-        # It's often suggested that the SIGHUP signal should be ignored before
-        # the second fork to avoid premature termination of the process.  The
-        # reason is that when the first child terminates, all processes, e.g.
-        # the second child, in the orphaned group will be sent a SIGHUP.
-        #
-        # "However, as part of the session management system, there are exactly
-        # two cases where SIGHUP is sent on the death of a process:
-        #
-        #    1) When the process that dies is the session leader of a session that
-        #        is attached to a terminal device, SIGHUP is sent to all processes
-        #        in the foreground process group of that terminal device.
-        #    2) When the death of a process causes a process group to become
-        #        orphaned, and one or more processes in the orphaned group are
-        #        stopped, then SIGHUP and SIGCONT are sent to all members of the
-        #        orphaned group." [2]
-        #
-        # The first case can be ignored since the child is guaranteed not to have
-        # a controlling terminal.  The second case isn't so easy to dismiss.
-        # The process group is orphaned when the first child terminates and
-        # POSIX.1 requires that every STOPPED process in an orphaned process
-        # group be sent a SIGHUP signal followed by a SIGCONT signal.  Since the
-        # second child is not STOPPED though, we can safely forego ignoring the
-        # SIGHUP signal.  In any case, there are no ill-effects if it is ignored.
-        #
-        # import signal              # Set handlers for asynchronous events.
-        # signal.signal(signal.SIGHUP, signal.SIG_IGN)
-
         try:
             # Fork a second child and exit immediately to prevent zombies.  This
             # causes the second child process to be orphaned, making the init
@@ -110,77 +44,23 @@ def createDaemon(function, logfile):
         except OSError as e:
             raise Exception("%s [%d]" % (e.strerror, e.errno))
 
-        if (pid == 0):  # The second child.
-            # We probably don't want the file mode creation mask inherited from
-            # the parent, so we give the child complete control over permissions.
-            if UMASK is not None:
-                os.umask(UMASK)
-        else:
+        if (pid != 0):
             # Parent (the first child) of the second child.
+            # exit() or _exit()?
+            # _exit is like exit(), but it doesn't call any functions registered
+            # with atexit (and on_exit) or any registered signal handlers.  It also
+            # closes any open file descriptors.  Using exit() may cause all stdio
+            # streams to be flushed twice and any temporary files may be unexpectedly
+            # removed.  It's therefore recommended that child branches of a fork()
+            # and the parent branch(es) of a daemon use _exit().
             os._exit(0)
     else:
-        # exit() or _exit()?
-        # _exit is like exit(), but it doesn't call any functions registered
-        # with atexit (and on_exit) or any registered signal handlers.  It also
-        # closes any open file descriptors.  Using exit() may cause all stdio
-        # streams to be flushed twice and any temporary files may be unexpectedly
-        # removed.  It's therefore recommended that child branches of a fork()
-        # and the parent branch(es) of a daemon use _exit().
         os.waitpid(pid, 0)
         return
 
-    # Close all open file descriptors.  This prevents the child from keeping
-    # open any file descriptors inherited from the parent.  There is a variety
-    # of methods to accomplish this task.  Three are listed below.
-    #
-    # Try the system configuration variable, SC_OPEN_MAX, to obtain the maximum
-    # number of open file descriptors to close.  If it doesn't exist, use
-    # the default value (configurable).
-    #
-    # try:
-    #     maxfd = os.sysconf("SC_OPEN_MAX")
-    # except (AttributeError, ValueError):
-    #     maxfd = MAXFD
-    #
-    # OR
-    #
-    # if (os.sysconf_names.has_key("SC_OPEN_MAX")):
-    #     maxfd = os.sysconf("SC_OPEN_MAX")
-    # else:
-    #     maxfd = MAXFD
-    #
-    # OR
-    #
-    # Use the getrlimit method to retrieve the maximum file descriptor number
-    # that can be opened by this process.  If there is no limit on the
-    # resource, use the default value.
-    #
-    import resource             # Resource usage information.
-    maxfd = resource.getrlimit(resource.RLIMIT_NOFILE)[1]
-    if (maxfd == resource.RLIM_INFINITY):
-        maxfd = MAXFD
-  
-    # Iterate through and close all file descriptors.
-#    for fd in range(0, maxfd):
-#        try:
-#            os.close(fd)
-#        except OSError:        # ERROR, fd wasn't open to begin with (ignored)
-#            pass
-
-    # Redirect the standard I/O file descriptors to the specified file.  Since
-    # the daemon has no controlling terminal, most daemons redirect stdin,
-    # stdout, and stderr to /dev/null.  This is done to prevent side-effects
-    # from reads and writes to the standard I/O file descriptors.
-
-    # This call to open is guaranteed to return the lowest file descriptor,
-    # which will be 0 (stdin), since it was closed above.
-#    os.open(REDIRECT_TO, os.O_RDWR)    # standard input (0)
-
-    # Duplicate standard input to standard output and standard error.
-#    os.dup2(0, 1)                      # standard output (1)
-#    os.dup2(0, 2)                      # standard error (2)
+    # The second child.
 
-    # Replace those fds with our own
+    # Replace standard fds with our own
     si = open('/dev/null', 'r')
     os.dup2(si.fileno(), sys.stdin.fileno())