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__clone(2) [netbsd man page]

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

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VFORK(2)						      BSD System Calls Manual							  VFORK(2)

NAME
vfork -- create a new process without copying the address space LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <unistd.h> pid_t vfork(void); DESCRIPTION
The vfork() system call can be used to create new processes without fully copying the address space of the old process, which is horrendously inefficient in a paged environment. It is useful when the purpose of fork(2) would have been to create a new system context for an execve(2). The vfork() system call differs from fork(2) in that the child borrows the parent's memory and thread of control until a call to execve(2) or an exit (either by a call to _exit(2) or abnormally). The parent process is suspended while the child is using its resources. The vfork() system call returns 0 in the child's context and (later) the pid of the child in the parent's context. The vfork() system call can normally be used just like fork(2). It does not work, however, to return while running in the child's context from the procedure that called vfork() since the eventual return from vfork() would then return to a no longer existent stack frame. Be careful, also, to call _exit(2) rather than exit(3) if you cannot execve(2), since exit(3) will flush and close standard I/O channels, and thereby mess up the parent processes standard I/O data structures. (Even with fork(2) it is wrong to call exit(3) since buffered data would then be flushed twice.) RETURN VALUES
Same as for fork(2). SEE ALSO
_exit(2), execve(2), fork(2), rfork(2), sigaction(2), wait(2), exit(3) HISTORY
The vfork() system call appeared in 2.9BSD. BUGS
To avoid a possible deadlock situation, processes that are children in the middle of a vfork() are never sent SIGTTOU or SIGTTIN signals; rather, output or ioctl(2) calls are allowed and input attempts result in an end-of-file indication. BSD
November 13, 2009 BSD
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