cpu_lwp_fork(9) [netbsd man page]

CPU_LWP_FORK(9) 					   BSD Kernel Developer's Manual					   CPU_LWP_FORK(9)

NAME

     cpu_lwp_fork, child_return, proc_trampoline -- finish a fork operation

SYNOPSIS

     #include <sys/proc.h>

     void
     cpu_lwp_fork(struct lwp *l1, struct lwp *l2, void *stack, size_t stacksize, void (*func)(void *), void *arg);

     void
     child_return(void *arg);

DESCRIPTION

     cpu_lwp_fork() is the machine-dependent portion of fork1() which finishes a fork operation, with child lwp l2 nearly set up.  It copies and
     updates the PCB and trap frame from the parent l1, making the child ready to run.

     cpu_lwp_fork() rigs the child's kernel stack so that it will start in proc_trampoline().  proc_trampoline() does not have a normal calling
     sequence and is entered by cpu_switch().  If an alternate user-level stack is requested (with non-zero values in both the stack and stacksize
     arguments), the user stack pointer is set up accordingly.

     After being entered by cpu_switch() and while running in user context (within the kernel) proc_trampoline() will invoke the function func
     with the argument arg.  If a kernel thread is being created, the return path and argument are specified with func and arg.  If a user process
     is being created, fork1() will pass child_return() and l2 to cpu_lwp_fork() as func and arg respectively.	This causes the newly-created
     child process to go directly to user level with an apparent return value of 0 from fork(2), while the parent process returns normally.

SEE ALSO

     fork(2), cpu_switchto(9), fork1(9)

BSD
								  April 13, 2010							       BSD

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