ref: a920c765f2b4130590fb5971a50690b21664957a
dir: /man/2/sys-export/
.TH SYS-EXPORT 2
.SH NAME
export \- export a name space
.SH SYNOPSIS
.EX
include "sys.m";
sys := load Sys Sys->PATH;
export: fn(fd: ref FD, dir: string, flag: int): int;
.EE
.SH DESCRIPTION
.B Export
receives and replies
to 9P requests from a client on a connection represented by
.IR fd ,
for file operations on the part of the current file name space
rooted at
.IR dir ,
which is thus exported.
This is the server end of the client's
.B mount
call.
Names presented by the client are interpreted relative to directory
.IR dir ,
which can be adjusted using
.IR sys-pctl (2)
and
.IR sys-bind (2)
before export.
The file descriptor
.I fd
must be open for reading and writing, and neither mounted elsewhere nor already exported.
.PP
Commonly,
.BR export 's
first argument is a file descriptor open on the data file in the
.B dir
of a
.B Connection
returned by
.B listen
(see
.IR dial (2)).
Before calling
.BR export ,
the connection on
.I fd
can optionally be authenticated and set for encryption or digesting using the
functions in
.IR security-auth (2).
.PP
The
.B export
function takes two mutually exclusive flags:
.TP
.B Sys->EXPWAIT
.B Export
blocks until all client requests are complete.
.TP
.B Sys->EXPASYNC
Client requests are handled by a background (kernel) process.
.B Export
returns immediately.
The serving process terminates when the client hangs up.
.SH EXAMPLES
.PP
Export a given directory on
.BR fd ,
protecting it from subsequent changes:
.IP
.EX
exportdir(fd: ref Sys->FD, dir: string, pid: chan of int)
{
pid <-= sys->pctl(Sys->FORKNS|Sys->FORKENV|Sys->NEWFD, fd.fd :: nil);
sys->export(fd, dir, Sys->EXPWAIT);
}
.EE
.PP
The
.B FORKNS
given to
.B pctl
forks the name space, and
prevents the
.B sys->export
from seeing the effects of subsequent mounts by the process
that calls or spawns
.BR exportdir .
The
.B exportdir
function above might be called using:
.IP
.EX
pid := chan of int;
spawn exportdir(fd, "/", pid);
expid := <-pid;
.EE
.PP
Service will stop automatically when the connection
.B fd
returns end-of-file (eg, when it hangs up),
but it can also be stopped locally by killing
.BR expid .
.EE
.SH SOURCE
.B /emu/port/inferno.c
.br
.B /emu/port/exportfs.c
.br
.B /os/port/inferno.c
.br
.B /os/port/exportfs.c
.SH DIAGNOSTICS
.B Export
returns a non-negative value on success and -1 on error;
the system error string is set.