| 2 |
- |
1 |
.TH MNT 3
|
|
|
2 |
.SH NAME
|
|
|
3 |
mnt \- attach to 9P servers
|
|
|
4 |
.SH SYNOPSIS
|
|
|
5 |
.nf
|
|
|
6 |
.B #M
|
|
|
7 |
.fi
|
|
|
8 |
.SH DESCRIPTION
|
|
|
9 |
The
|
|
|
10 |
.I mount driver
|
|
|
11 |
is used by the
|
|
|
12 |
.B mount
|
|
|
13 |
system call
|
|
|
14 |
(but not
|
|
|
15 |
.BR bind ;
|
|
|
16 |
see
|
|
|
17 |
.IR bind (2))
|
|
|
18 |
to connect the name space of a process to
|
|
|
19 |
the service provided by a 9P server over a communications channel.
|
|
|
20 |
After the
|
|
|
21 |
.BR mount ,
|
|
|
22 |
system calls involving files in that portion of the name space will
|
|
|
23 |
be converted by the mount driver into the appropriate
|
|
|
24 |
9P messages to the server.
|
|
|
25 |
.PP
|
|
|
26 |
The
|
|
|
27 |
.I mount
|
|
|
28 |
system call issues
|
|
|
29 |
.I session
|
|
|
30 |
and
|
|
|
31 |
.IR attach (5)
|
|
|
32 |
messages to the server to identify and validate the user of the connection.
|
|
|
33 |
Each distinct user of a connection must mount it separately;
|
|
|
34 |
the mount driver multiplexes the access of the various users and their
|
|
|
35 |
processes to the service.
|
|
|
36 |
.PP
|
|
|
37 |
File-oriented system calls are converted by the kernel into messages in the 9P protocol.
|
|
|
38 |
Within the kernel, 9P is implemented by procedure calls to the
|
|
|
39 |
various kernel device drivers.
|
|
|
40 |
The mount driver translates these procedure calls into remote procedure calls
|
|
|
41 |
to be transmitted as messages over the communication channel to the server.
|
|
|
42 |
Each message is implemented by a write
|
|
|
43 |
of the corresponding protocol message to the server channel
|
|
|
44 |
followed by a read on the server channel to get the reply.
|
|
|
45 |
Errors in the reply message are turned into system call error returns.
|
|
|
46 |
.PP
|
|
|
47 |
A
|
|
|
48 |
.IR read (2)
|
|
|
49 |
or
|
|
|
50 |
.IR write
|
|
|
51 |
system call on a file served by the mount driver
|
|
|
52 |
may be translated
|
|
|
53 |
into more than one
|
|
|
54 |
message,
|
|
|
55 |
since there is a maximum data size for a 9P message.
|
|
|
56 |
The system call
|
|
|
57 |
will return when the specified number of bytes have been transferred
|
|
|
58 |
or a short reply is returned.
|
|
|
59 |
.PP
|
|
|
60 |
The string
|
|
|
61 |
.L #M
|
|
|
62 |
is an illegal file name,
|
|
|
63 |
so this device can only be accessed directly by the kernel.
|
|
|
64 |
.SH "SEE ALSO"
|
|
|
65 |
.IR bind (2)
|
|
|
66 |
.SH SOURCE
|
|
|
67 |
.B /sys/src/9/port/devmnt.c
|
|
|
68 |
.SH BUGS
|
|
|
69 |
When mounting a service through the mount driver,
|
|
|
70 |
that is, when the channel being multiplexed is itself
|
|
|
71 |
a file being served by the mount driver,
|
|
|
72 |
large messages may be broken in two.
|