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.TH BIND 2

.SH NAME

bind, mount, unmount \- change name space

.SH SYNOPSIS

.B #include <u.h>

.br

.B #include <libc.h>

.PP

.B

int bind(char *name, char *old, int flag)

.PP

.B

int mount(int fd, int afd, char *old, int flag, char *aname)

.PP

.B

int unmount(char *name, char *old)

.SH DESCRIPTION

.I Bind

and

.I mount

modify the file name space of the current process and other

processes in its name space group

(see

.IR fork (2)).

For both calls,

.I old

is the name of an existing file or directory in the

current name space where the modification is to be made.

The name

.I old

is

.I evaluated

as described in

.IR intro (2),

except that no translation of the final path element is done.

.PP

For

.IR bind ,

.I name

is the name of another (or possibly the same)

existing file or directory in

the current name space.

After a successful

.I bind

call, the file name

.I old

is an alias for the object originally named by

.IR name ;

if the modification doesn't hide it,

.I name

will also still refer to its original file.

The evaluation of

.I new

happens at the time of the

.IR bind ,

not when the binding is later used.

.PP

The

.I fd

argument to

.I mount

is a file descriptor of an open network connection

or pipe to a file server, while

.I afd

is a authentication file descriptor as created by

.IR fauth (2)

and subsequently authenticated.

If authentication is not required,

.I afd

should be -1.

The

.I old

file must be a directory.

After a successful

.I mount

the file tree

.I served

(see below) by

.I fd

will be visible with its root directory having name

.IR old .

.PP

The

.I flag

controls details of the modification made to the name space.

In the following,

.I new

refers to the file

as defined by

.I name

or the root directory served by

.IR fd .

Either both

.I old

and new files must be directories,

or both must not be directories.

.I Flag

can be one of:

.TF MBEFORE

.TP 

.B MREPL

Replace the

.I old

file by the new one.

Henceforth, an evaluation of

.I old

will be translated to the new file.

If they are directories (for

.IR mount ,

this condition is true by definition),

.I old

becomes a

.I "union directory"

consisting of one directory (the new file).

.TP

.B MBEFORE

Both the

.I old

and new files must be directories.

Add the constituent files of the new directory

to the union directory at

.I old

so its contents appear first in the union.

After an

.B MBEFORE

.I bind

or

.IR mount ,

the new directory will be searched first when evaluating file names

in the union directory.

.TP

.B MAFTER

Like

.B MBEFORE

but the new directory goes at the end of the union.

.PD

.PP

The flags are defined in

.BR <libc.h> .

In addition, there is an

.B MCREATE

flag that can be OR'd with any of the above.

When a

.I create

system call (see

.IR open (2))

attempts to create in a union directory, and the file does not exist,

the elements of the union are searched in order until one is found

with

.B MCREATE

set.

The file is created in that directory; if that attempt fails,

the

.I create

fails.

.PP

Finally, the

.B MCACHE

flag, valid for

.I mount

only, turns on caching for files made available by the mount.

By default, file contents are always retrieved from the server.

With caching enabled, the kernel may instead use a local cache to satisfy

.IR read (5)

requests for files accessible through this mount point.

The currency of cached data for a file is verified at each

.IR open (5)

of the file from this client machine.

.PP

With

.IR mount ,

the file descriptor

.I fd

must be open for reading and writing

and prepared to respond to 9P messages

(see Section 5).

After the

.IR mount ,

the file tree starting at

.I old

is served by a kernel

.IR mnt (3)

device.

That device will turn operations in the tree into messages on

.IR fd .

.I Aname

selects among different

file trees on the server; the null string chooses the default tree.

.PP

The file descriptor

.I fd

is automatically closed by a successful

.I mount

call.

.PP

The effects of

.I bind

and

.I mount

can be undone by

.IR unmount .

If

.I name

is zero, everything bound to or mounted upon

.I old

is unbound or unmounted.

If

.I name

is not zero, it is evaluated as described above for

.IR bind ,

and the effect of binding or mounting that particular result on

.I old

is undone.

.SH SOURCE

.B /sys/src/libc/9syscall

.SH SEE ALSO

.IR bind (1),

.IR intro (2),

.IR fcall (2),

.IR auth (2)

(particularly

.BR amount ),

.IR intro (5),

.IR mnt (3),

.IR srv (3)

.SH DIAGNOSTICS

The return value is a positive integer (a unique sequence number) for

success, -1 for failure.

These routines set

.IR errstr .

.SH BUGS

.I Mount

will not return until it has successfully attached

to the file server, so the process doing a

.I mount

cannot be the one serving.