MOUNT_PORTALFS(8)

NAME
mount_portalfs - mount the portal daemon

SYNOPSIS
mount_portalfs [-o options] /etc/portal.conf mount_point

DESCRIPTION
The mount_portalfs utility attaches an instance of the portal daemon to the global file system namespace. The conventional mount point is /p. This command is normally executed by mount(8) at boot time.

The options are as follows:

-o  Options are specified with a -o flag followed by a comma separated string of options. See the mount(8) man page for possible options and their meanings.

The portal daemon provides an open service. Objects opened under the portal mount point are dynamically created by the portal daemon according to rules specified in the named configuration file. Using this mechanism allows descriptors such as sockets to be made available in the file system namespace.

The portal daemon works by being passed the full pathname of the object being opened. The daemon creates an appropriate descriptor according to the rules in the configuration file, and then passes the descriptor back to the calling process as the result of the open system call.

NAMESPACE
By convention, the portal daemon divides the namespace into sub-namespaces, each of which handles objects of a particular type.

The following sub-namespaces are currently implemented: fs, pipe, tcp, and tcplisten.

The fs namespace opens the named file, starting back at the root directory. This can be used to provide a controlled escape path from a chrooted environment.

The pipe namespace executes the named command, starting back at the root directory. The command's arguments can be provided after the command's name, by separating them with spaces or tabs. Files opened for reading in the pipe namespace will receive their input from the command's standard output; files opened for writing will send the data of write operations to the command's standard input.

The tcp namespace takes a slash separated hostname and a port and creates an open TCP/IP connection.

The tcplisten namespace takes a slash separated hostname and port and creates a TCP/IP socket bound to the given hostname-port pair. The hostname may be specified as "ANY" to allow any other host to connect to the socket. A port number of 0 will dynamically allocate a port, this can be discovered by calling getsockname(2) with the returned file descriptor. Privileged ports can only be bound to by the super-user.

CONFIGURATION FILE
The configuration file contains a list of rules. Each rule takes one line and consists of two or more whitespace separated fields. A hash (``#'') character causes the remainder of a line to be ignored. Blank lines are ignored.

The first field is a pathname prefix to match against the requested pathname. If a match is found, the second field tells the daemon what type of object to create. Subsequent fields are passed to the creation function.

    # @(#)portal.conf	5.1 (Berkeley) 7/13/92
    tcplisten/	tcplisten tcplisten/
    tcp/		tcp tcp/
    fs/		file fs/
    pipe/		pipe pipe/

FILES
/p/*

EXAMPLES
Display the greeting of the FreeBSD SMTP server.

    head -1 /p/tcp/mx1.freebsd.org/smtp

Implement a (single-threaded) echo server:

    while :
    do
        (exec 3<>/p/tcplisten/ANY/echo && cat -u <&3 >&3)
    done

Gather data from two sources. Verify that two remote files are identical:

    diff -q '/p/pipe/usr/bin/fetch -o - \
            ftp://ftp1.freebsd.org/pub/FreeBSD/README.TXT' \
        '/p/pipe/usr/bin/fetch -o - \
            ftp://ftp2.freebsd.org/pub/FreeBSD/README.TXT'

Scatter data to two sinks. Record a remote CD ISO image and calculate its checksum:

    fetch -o - ftp://ftp5.freebsd.org/.../disc.iso |
    tee '/p/pipe/usr/local/bin/cdrecord -' |
    md5

Create an XML view of the password file:

    ln -s '/p/pipe/usr/local/bin/passwd2xml /etc/passwd' \
        /etc/passwd.xml"

SEE ALSO
mount(2), unmount(2), fstab(5), mount(8) W. Richard Stevens, Jan-Simon Pendry, Portals in 4.4BSD, USENIX 1995 Technical Conference Proceedings, Berkeley, CA, Peter Honeyman.

HISTORY
The mount_portalfs utility first appeared in 4.4BSD.

CAVEATS
This file system may not be NFS-exported.