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authorRichard Purdie <richard.purdie@linuxfoundation.org>2017-07-31 12:12:45 +0100
committerRichard Purdie <richard.purdie@linuxfoundation.org>2017-07-31 13:04:26 +0100
commit3daa9001269e5b9156d0eb3299d2628d2d219fff (patch)
tree5b1ba2bbb41377b84c01add1c044d1f0091560be
parentdec1d2c26f6cb3ffeb44beaab0129cd531a6d08b (diff)
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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>
-rw-r--r--lib/bb/daemonize.py148
1 files changed, 14 insertions, 134 deletions
diff --git a/lib/bb/daemonize.py b/lib/bb/daemonize.py
index a4664ad76b..a5a9d868d0 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())