Forking, vforking or rforking are the only ways new processes are created.
The
Fa 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 open file descriptor table (which, when shared, permits processes
to open and close files for other processes),
and open files.
The
Fa flags
argument
is the logical OR of some subset of:
RFPROC
If set a new process is created; otherwise changes affect the
current process.
RFNOWAIT
If set, the child process will be dissociated from the parent.
Upon
exit the child will not leave a status for the parent to collect.
See
wait(2).
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
RFTHREAD
If set, the new process shares file descriptor to process leaders table
with its parent.
Only applies when neither
RFFDG
nor
RFCFDG
are set.
RFMEM
If set, the kernel will force sharing of the entire address space,
typically by sharing the hardware page table directly.
The child
will thus inherit and share all the segments the parent process owns,
whether they are normally shareable or not.
The stack segment is
not split (both the parent and child return on the same stack) and thus
rfork ();
with the RFMEM flag may not generally be called directly from high level
languages including C.
May be set only with
RFPROC
A helper function is provided to assist with this problem and will cause
the new process to run on the provided stack.
See
rfork_thread3
for information.
RFSIGSHARE
If set, the kernel will force sharing the sigacts structure between the
child and the parent.
RFLINUXTHPN
If set, the kernel will return SIGUSR1 instead of SIGCHILD upon thread
exit for the child.
This is intended to mimic certain Linux clone behaviour.
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 id's range from 1 to the maximum integer
( int )
value.
The
rfork ();
system call
will sleep, if necessary, until required process resources are available.
The
fork ();
system call
can be implemented as a call to
rfork (RFFDG | RFPROC);
but is not for backwards compatibility.
RETURN VALUES
Upon successful completion,
rfork ();
returns a value
of 0 to the child process and returns the process ID of the child
process to the parent process.
Otherwise, a value of -1 is returned
to the parent process, no child process is created, and the global
variable
errno
is set to indicate the error.
ERRORS
The
rfork ();
system call
will fail and no child process will be created if:
Bq Er EAGAIN
The system-imposed limit on the total
number of processes under execution would be exceeded.
The limit is given by the
sysctl(3)
MIB variable
KERN_MAXPROC
(The limit is actually ten less than this
except for the super user).
Bq Er EAGAIN
The user is not the super user, and
the system-imposed limit
on the total number of
processes under execution by a single user would be exceeded.
The limit is given by the
sysctl(3)
MIB variable
KERN_MAXPROCPERUID
Bq Er EAGAIN
The user is not the super user, and
the soft resource limit corresponding to the
Fa resource
argument
RLIMIT_NOFILE
would be exceeded (see
getrlimit(2)).
Bq Er EINVAL
Both the RFFDG and the RFCFDG flags were specified.
Bq Er EINVAL
Any flags not listed above were specified.
Bq Er ENOMEM
There is insufficient swap space for the new process.
Fx does not yet implement a native
clone ();
library call, and the current pthreads implementation does not use
rfork ();
with RFMEM.
A native port of the linux threads library,
/usr/ports/devel/linuxthreads
contains a working
clone ();
call that utilizes RFMEM.
The
rfork_thread3
function can often be used instead of
clone (.);
