72 lines
1.9 KiB
Text
72 lines
1.9 KiB
Text
.TH MNT 3
|
|
.SH NAME
|
|
mnt \- attach to 9P servers
|
|
.SH SYNOPSIS
|
|
.nf
|
|
.B #M
|
|
.fi
|
|
.SH DESCRIPTION
|
|
The
|
|
.I mount driver
|
|
is used by the
|
|
.B mount
|
|
system call
|
|
(but not
|
|
.BR bind ;
|
|
see
|
|
.IR bind (2))
|
|
to connect the name space of a process to
|
|
the service provided by a 9P server over a communications channel.
|
|
After the
|
|
.BR 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.
|
|
.PP
|
|
The
|
|
.I mount
|
|
system call issues
|
|
.I session
|
|
and
|
|
.IR attach (5)
|
|
messages to the server to identify and validate 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 service.
|
|
.PP
|
|
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 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.
|
|
.PP
|
|
A
|
|
.IR read (2)
|
|
or
|
|
.IR 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.
|
|
.PP
|
|
The string
|
|
.L #M
|
|
is an illegal file name,
|
|
so this device can only be accessed directly by the kernel.
|
|
.SH "SEE ALSO"
|
|
.IR bind (2)
|
|
.SH SOURCE
|
|
.B /sys/src/9/port/devmnt.c
|
|
.SH 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.
|