MNT(3) MNT(3)
NAME
mnt - attach to 9P servers
SYNOPSIS
#M
DESCRIPTION
The mount driver is used by the mount system call (but not
bind; see bind(2)) to connect the name space of a process to
the service provided by a 9P server over a communications
channel. After the mount, system calls involving files in
that portion of the name space will be converted by the
mount driver into the appropriate 9P messages to the server.
The mount system call issues an auth(5) message to the
server to validate the user and an attach(5) message to
identify the user of the connection. Each distinct user of
a connection must mount it separately; the mount driver mul-
tiplexes the access of the various users and their processes
to the service.
File-oriented system calls are converted by the kernel into
messages in the 9P protocol. Within the kernel, 9P is
implemented by procedure calls to the various kernel device
drivers. The mount driver translates these procedure calls
into remote procedure calls to be transmitted as messages
over the communication channel to the server. Each message
is implemented by a write of the corresponding protocol mes-
sage to the server channel followed by a read on the server
channel to get the reply. Errors in the reply message are
turned into system call error returns.
A read(2) or write system call on a file implemented by the
mount driver may be translated into more than one message,
since there is a maximum data size for a 9P message. The
system call will return when the specified number of bytes
have been transferred or a short reply is returned.
The string `#M' is an illegal file name, so this device can
only be accessed directly by the kernel.
BUGS
It is not possible to mount a service through the mount
driver across a network. As a result the window command
will not work from the CPU server since it cannot mount the
srv entry for 8½.
SEE ALSO
bind(2)
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