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Diffstat (limited to 'lib/libc/sys/rfork.2')
| -rw-r--r-- | lib/libc/sys/rfork.2 | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/lib/libc/sys/rfork.2 b/lib/libc/sys/rfork.2 new file mode 100644 index 0000000..c5825cb --- /dev/null +++ b/lib/libc/sys/rfork.2 @@ -0,0 +1,145 @@ +.\" +.\" This manual page is taken directly from Plan9, and modified to +.\" describe the actual BSD implementation. Permission for +.\" use of this page comes from Rob Pike <rob@plan9.att.com>. +.\" +.\" $FreeBSD$ +.\" +.Dd Jan 12, 1996 +.Dt RFORK 2 +.Os +.Sh NAME +.Nm rfork +.Nd manipulate process resources +.Sh SYNOPSIS +.Fd #include <unistd.h> +.Ft int +.Fn rfork "int flags" +.Sh DESCRIPTION +Forking, vforking or rforking are the only ways new processes are created. +The +.Fa flags +argument to +.Fn 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. +.Fa Flags +is the logical OR of some subset of: +.Bl -tag -width "RFCNAMEG" -compact -offset indent +.It RFPROC +If set a new process is created; otherwise changes affect the +current process. +The current implementation requires this flag to always be set. +.It 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 +.Xr wait 2 . +.It RFFDG +If set, the invoker's file descriptor table (see +.Xr intro 2 +) is copied; otherwise the two processes share a +single table. +.It RFCFDG +If set, the new process starts with a clean file descriptor table. +Is mutually exclusive with +.Dv RFFDG . +.It RFMEM +If set, the kernel will force sharing of the entire address space. +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 +.Dv RFPROC . +.It RFSIGSHARE +If set, the kernel will force sharing the sigacts structure between the +child and the parent. +.It 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. +.El +.Pp +File descriptors in a shared file descriptor table are kept +open until either they are explicitly closed +or all processes sharing the table exit. +.Pp +If +.Dv 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 +.Dv RFPROC , +the return value is zero. +Process id's range from 1 to the maximum integer +.Ft ( int ) +value. +.Fn Rfork +will sleep, if necessary, until required process resources are available. +.Pp +.Fn Fork +can be implemented as a call to +.Fn rfork "RFFDG | RFPROC" +but isn't for backwards compatibility. +.Sh RETURN VALUES +Upon successful completion, +.Fn 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 +.Va errno +is set to indicate the error. +.Sh ERRORS +.Fn Rfork +will fail and no child process will be created if: +.Bl -tag -width [EAGAIN] +.It Bq Er EAGAIN +The system-imposed limit on the total +number of processes under execution would be exceeded. +The limit is given by the +.Xr sysctl 3 +MIB variable +.Dv KERN_MAXPROC . +(The limit is actually one less than this +except for the super user). +.It 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 +.Xr sysctl 3 +MIB variable +.Dv KERN_MAXPROCPERUID . +.It Bq Er EAGAIN +The user is not the super user, and +the soft resource limit corresponding to the resource parameter +.Dv RLIMIT_NOFILE +would be exceeded (see +.Xr getrlimit 2 ) . +.It Bq Er EINVAL +The RFPROC flag was not specified. +.It Bq Er EINVAL +Both the RFFDG and the RFCFDG flags were specified. +.It Bq Er ENOMEM +There is insufficient swap space for the new process. +.El +.Sh SEE ALSO +.Xr fork 2 , +.Xr intro 2 , +.Xr minherit 2 , +.Xr vfork 2 +.Sh HISTORY +The +.Fn rfork +function call first appeared in Plan9. |
