child_return(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

FORK1(9)						   BSD Kernel Developer's Manual						  FORK1(9)

NAME

     fork1 -- create a new process

SYNOPSIS

     #include <sys/types.h>
     #include <sys/proc.h>

     int
     fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize, void (*func)(void *), void *arg, register_t *retval,
	 struct proc **rnewprocp);

DESCRIPTION

     fork1() creates a new process out of the process behind l1, which is assumed to be the current lwp.  This function is used primarily to
     implement the fork(2) and vfork(2) system calls, but is versatile enough to be used as a backend for e.g. the __clone(2) call.

     The flags argument controls the semantics of the fork operation, and is made up of the bitwise-OR of the following values:

     FORK_PPWAIT      The parent process will sleep until the child process successfully calls execve(2) or exits (either by a call to _exit(2) or
		      abnormally).

     FORK_SHAREVM     The child process will share the parent's virtual address space.	If this flag is not specified, the child will get a copy-
		      on-write snapshot of the parent's address space.

     FORK_SHARECWD    The child process will share the parent's current directory, root directory, and file creation mask.

     FORK_SHAREFILES  The child process will share the parent's file descriptors.

     FORK_SHARESIGS   The child process will share the parent's signal actions.

     FORK_NOWAIT      The child process will at creation time be inherited by the init process.

     FORK_CLEANFILES  The child process will not copy or share the parent's descriptors, but rather will start out with a clean set.

     A flags value of 0 indicates a standard fork operation.

     The exitsig argument controls the signal sent to the parent on child death.  If normal operation desired, SIGCHLD should be supplied.

     It is possible to specify the child userspace stack location and size by using the stack and stacksize arguments, respectively.  Values NULL
     and 0, respectively, will give the child the default values for the machine architecture in question.

     The arguments func and arg can be used to specify a kernel function to be called when the child process returns instead of child_return().
     These are used for example in starting the init process and creating kernel threads.

     The retval argument is provided for the use of system call stubs.	If retval is not NULL, it will hold the following values after successful
     completion of the fork operation:

     retval[0]	This will contain the pid of the child process.

     retval[1]	In the parent process, this will contain the value 0.  In the child process, this will contain 1.

     User level system call stubs typically subtract 1 from retval[1] and bitwise-AND it with retval[0], thus returning the pid to the parent
     process and 0 to the child.

     If rnewprocp is not NULL, *rnewprocp will point to the newly created process upon successful completion of the fork operation.

RETURN VALUES

     Upon successful completion of the fork operation, fork1() returns 0.  Otherwise, the following error values are returned:

     [EAGAIN]  The limit on the total number of system processes would be exceeded.

     [EAGAIN]  The limit RLIMIT_NPROC on the total number of processes under execution by this user id would be exceeded.

SEE ALSO

     execve(2), fork(2), vfork(2)

BSD
								  January 4, 2008							       BSD