freebsd-dev/share/man/man5/fdesc.5

.\" Copyright (c) 1996
.\"	Mike Pritchard <mpp@FreeBSD.org>.  All rights reserved.
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.\" Jan-Simon Pendry.
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.Dd December 14, 1996
.Dt FDESC 5
.Os BSD 4.4
.Sh NAME
.Nm fdesc
.Nd file-descriptor file system
.Sh SYNOPSIS
fdesc	/dev/fd	fdesc rw 0 0
.Sh DESCRIPTION
The file-descriptor file system, or
.Nm fdesc ,
provides access to the per-process file descriptor
namespace in the global filesystem namespace.
The conventional mount point is
.Pa /dev/fd .
.Pp
The file system's contents
appear as a list of numbered files
which correspond to the open files of the process reading the
directory.
The files
.Pa /dev/fd/0
through
.Pa /dev/fd/#
refer to file descriptors which can be accessed through the file
system.
If the file descriptor is open and the mode the file is being opened
with is a subset of the mode of the existing descriptor, the call:
.Bd -literal -offset indent
fd = open("/dev/fd/0", mode);
.Ed
.Pp
and the call:
.Bd -literal -offset indent
fd = fcntl(0, F_DUPFD, 0);
.Ed
.Pp
are equivalent.
.Pp
Flags to the
.Xr open 2
call other than
.Dv O_RDONLY , 
.Dv O_WRONLY
and
.Dv O_RDWR
are ignored.
.Sh FILES
.Bl -tag -width /dev/stderr -compact
.It Pa /dev/fd/#
.El
.Sh SEE ALSO
.Xr mount_devfs 8 ,
.Xr mount_fdesc 8
.Sh HISTORY
The
.Nm 
filesystem first appeared in
.Bx 4.4 .
The 
.Nm
manual page first appeared in 
.Fx 2.2 .
.Sh AUTHORS
The 
.Nm
manual page was written by
.An Mike Pritchard Aq mpp@FreeBSD.org ,
and was based on the 
.Xr mount_fdesc 8
manual page written by
.An Jan-Simon Pendry .