MNT(3) MNT(3)
NAME
mnt - attach to 9P servers
SYNOPSIS
#M
DESCRIPTION
The mount driver is used by Sys->mount (but not Sys->bind;
see sys-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, file operations in that portion
of the name space will be converted by the mount driver into
the appropriate 9P messages to the server, and its 9P
replies returned as the status of the system calls.
Any authentication must precede mount, which does none
itself; see security-intro(2) for a discussion of the
authentication and security mechanisms provided `ready made'
by Inferno, but any other scheme can be agreed between
client and server. The mount system call does, however,
issue an attach(5) message to the server to identify the
user of the connection. 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 ser-
vice.
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, as described in intro(10) and dev(10.2). The mount
driver translates these procedure calls into remote proce-
dure calls to be transmitted as messages over the communica-
tion channel to the server. Each message is implemented by
a write of the corresponding protocol message 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 sys-read(2) or Sys->write system call on a file served by
the mount driver may be translated into more than one mes-
sage, 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
be accessed directly only by the kernel.
SEE ALSO
bind(1), sys-bind(2)
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MNT(3) MNT(3)
SOURCE
/emu/port/devmnt.c
/os/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
two.
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