237 lines
4.6 KiB
Plaintext
237 lines
4.6 KiB
Plaintext
.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.
|