73 lines
1.9 KiB
Plaintext
73 lines
1.9 KiB
Plaintext
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.TH MNT 3
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.SH NAME
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mnt \- attach to 9P servers
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.SH SYNOPSIS
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.nf
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.B #M
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.fi
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.SH DESCRIPTION
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The
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.I mount driver
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is used by the
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.B mount
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system call
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(but not
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.BR bind ;
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see
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.IR bind (2))
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to connect the name space of a process to
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the service provided by a 9P server over a communications channel.
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After the
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.BR mount ,
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system calls involving files in that portion of the name space will
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be converted by the mount driver into the appropriate
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9P messages to the server.
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.PP
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The
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.I mount
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system call issues
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.I session
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and
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.IR attach (5)
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messages to the server to identify and validate the user of the connection.
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Each distinct user of a connection must mount it separately;
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the mount driver multiplexes the access of the various users and their
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processes to the service.
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.PP
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File-oriented system calls are converted by the kernel into messages in the 9P protocol.
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Within the kernel, 9P is implemented by procedure calls to the
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various kernel device drivers.
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The mount driver translates these procedure calls into remote procedure calls
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to be transmitted as messages over the communication channel to the server.
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Each message is implemented by a write
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of the corresponding protocol message to the server channel
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followed by a read on the server channel to get the reply.
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Errors in the reply message are turned into system call error returns.
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.PP
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A
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.IR read (2)
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or
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.IR write
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system call on a file served by the mount driver
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may be translated
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into more than one
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message,
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since there is a maximum data size for a 9P message.
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The system call
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will return when the specified number of bytes have been transferred
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or a short reply is returned.
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.PP
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The string
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.L #M
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is an illegal file name,
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so this device can only be accessed directly by the kernel.
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.SH "SEE ALSO"
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.IR bind (2)
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.SH SOURCE
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.B /sys/src/9/port/devmnt.c
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.SH BUGS
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When mounting a service through the mount driver,
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that is, when the channel being multiplexed is itself
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a file being served by the mount driver,
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large messages may be broken in two.
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