fork, rfork - manipulate process resources
int rfork(int flags)
Forking is the only way new processes are created. The flags argument to rfork selects
which resources of the invoking process (parent) are shared by the new process (child) or
initialized to their default values. The resources include the file name space, the open
file descriptor table (which, when shared, permits processes to open and close files for
other processes), the set of environment variables (see env(3)), the note group (the set
of processes that receive notes written to a member's notepg file; see proc(3)), and open
files. Flags is the logical OR of some subset of
RFPROC If set a new process is created; otherwise changes affect the current process.
If set, the child process will be dissociated from the parent. Upon exit the child
will leave no Waitmsg (see wait(2)) for the parent to collect.
If set, the new process inherits a copy of the parent's name space; otherwise the
new process shares the parent's name space. The tag space for rendezvous(2) is
considered part of the name space. Is mutually exclusive with RFCNAMEG.
If set, the new process starts with a clean name space. A new name space must be
built from a mount of an open file descriptor. Is mutually exclusive with RFNAMEG.
RFENVG If set, the environment variables are copied; otherwise the two processes share
environment variables. Is mutually exclusive with RFCENVG.
If set, the new process starts with an empty environment. Is mutually exclusive
Each process is a member of a group of processes that all receive notes when a note
is written to any of their notepg files (see proc(3)). The group of a new process
is by default the same as its parent, but if RFNOTEG is set (regardless of RFPROC),
the process becomes the first in a new group, isolated from previous processes.
RFFDG If set, the invoker's file descriptor table (see intro(2)) is copied; otherwise the
two processes share a single table.
RFCFDG If set, the new process starts with a clean file descriptor table. Is mutually
exclusive with RFFDG.
RFMEM If set, the kernel will mark segments of type data and bss as shared. The child
will then inherit all the shared segments the parent process owns. Other segment
types will be unaffected. Subsequent forks by the parent will then propagate the
shared data and bss between children. The stack segment is always split. May be
set only with RFPROC.
File descriptors in a shared file descriptor table are kept open until either they are
explicitly closed or all processes sharing the table exit.
If RFPROC is set, the value returned in the parent process is the process id of the child
process; the value returned in the child is zero. Without RFPROC, the return value is
zero. Process ids range from 1 to the maximum integer (int) value. Rfork will sleep, if
necessary, until required process resources are available.
Fork is just a call of rfork(RFFDG|RFPROC).
These functions set errstr.