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 session and attach(5) messages
to the server to identify and validate the user of the con-
nection. Each distinct user of a connection must mount it
separately; the mount driver multiplexes 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 served 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.
SEE ALSO
bind(2)
SOURCE
/sys/src/9/port/devmnt.c
BUGS
When mounting a service through the mount driver, that is,
when the channel being multiplexed is itself a file being
served by the mount driver, large messages may be broken in
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two.
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