netbsd man page for __clone

CLONE(2)						      BSD System Calls Manual							  CLONE(2)

NAME
     clone, __clone -- spawn new process with options

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sched.h>

     pid_t
     clone(int (*func)(void *arg), void *stack, int flags, void *arg);

     pid_t
     __clone(int (*func)(void *arg), void *stack, int flags, void *arg);

DESCRIPTION
     The clone system call (and associated library support code) creates a new process in a way that allows the caller to specify several options
     for the new process creation.

     Unlike fork(2) or vfork(2), in which the child process returns to the call site, clone causes the child process to begin execution at the
     function specified by func.  The argument arg is passed to the entry point, as a means for the parent to provide context to the child.  The
     stack pointer for the child process will be set to stack.	Note that the clone interface requires that the application know the stack direc-
     tion for the architecture, and that the caller initialize the stack argument as appropriate for the stack direction.

     The flags argument specifies several options that control how the child process is created.  The lower 8 bits of flags specify the signal
     that is to be sent to the parent when the child exits.  The following flags may also be specified by bitwise-or'ing them with the signal
     value:

       CLONE_VM       Share the virtual address space with the parent.	The address space is shared in the same way as vfork(2).

       CLONE_FS       Share the ``file system information'' with the parent.  This include the current working directory and file creation mask.

       CLONE_FILES    Share the file descriptor table with the parent.

       CLONE_SIGHAND  Share the signal handler set with the parent.  Note that the signal mask is never shared between the parent and the child,
		      even if CLONE_SIGHAND is set.

       CLONE_VFORK    Preserve the synchronization semantics of vfork(2); the parent blocks until the child exits.

     The clone call returns the pid of the child in the parent's context.  The child is provided no return value, since it begins execution at a
     different address.

     If the child process's entry point returns, the value it returns is passed to _exit(2), and the child process exits.  Note that if the child
     process wants to exit directly, it should use _exit(2), and not exit(3), since exit(3) will flush and close standard I/O channels, and
     thereby corrupt the parent process's standard I/O data structures (even with fork(2) it is wrong to call exit(3) since buffered data would
     then be flushed twice).

     Note that clone is not intended to be used for new native NetBSD applications.  It is provided as a means to port software originally written
     for the Linux operating system to NetBSD.

RETURN VALUES
     Same as for fork(2).

ERRORS
     Same as for fork(2).

SEE ALSO
     chdir(2), chroot(2), fork(2), sigaction(2), sigprocmask(2), umask(2), vfork(2), wait(2)

HISTORY
     The clone() function call appeared in NetBSD 1.6.	It is compatible with the Linux function call of the same name with respect to the
     described options.

BUGS
     The NetBSD implementation of clone() does not implement the following flags that are present in the Linux implementation:

	   o   CLONE_CHILD_CLEARTID
	   o   CLONE_CHILD_SETTID
	   o   CLONE_IO
	   o   CLONE_NEWIPC
	   o   CLONE_NEWNET
	   o   CLONE_NEWNS
	   o   CLONE_NEWPID
	   o   CLONE_NEWUTS
	   o   CLONE_PARENT
	   o   CLONE_PARENT_SETTID
	   o   CLONE_PID
	   o   CLONE_PTRACE
	   o   CLONE_SETTLS
	   o   CLONE_STOPPED
	   o   CLONE_SYSVSEM
	   o   CLONE_THREAD
	   o   CLONE_UNTRACED

BSD
								    May 4, 2010 							       BSD