SYS-BIND(2)SYS-BIND(2)NAME
bind, mount, unmount - change file name space
SYNOPSIS
include "sys.m";
sys := load Sys Sys->PATH;
bind: fn(name, old: string, flag: int): int;
mount: fn(fd: ref FD; afd: ref FD, old: string, flag: int, aname: string):
int;
unmount: fn(name, old: string): int;
DESCRIPTION
Bind and mount modify the file name space of the current process and
its name space group. For both calls, old is the name of an existing
file or directory in the current name space where the modification is
to be made. The name old is evaluated as described in sys-intro(2)
except that no translation of the final path element is done.
For bind, name is the name of another (or possibly the same) existing
file or directory in the current name space. After a successful bind
call, the file name old is an alias for the object originally named by
name; if the modification does not hide the original, name will also
still refer to its original file. The evaluation of name happens at
the time of the bind, not when the binding is later used.
The fd argument to mount is a file descriptor of an open pipe or net‐
work connection to a file server ready to receive 9P messages. The old
file must be a directory. After a successful mount, the file tree
served (see below) by fd will be visible with its root directory having
name old. If the requested service requires authentication, the file
descriptor afd must be open on an authentication file for the requested
service; otherwise it should be nil.
The flag controls details of the modification made to the name space.
In the following, new refers to the file as defined by name or the root
directory served by fd. Either both old and new files must be directo‐
ries, or both must not be directories. Flag can be one of:
Sys->MREPL
Replace the old file by the new one. Henceforth, an evaluation
of old will be translated to the new file. If they are directo‐
ries (for mount, this condition is true by definition), old
becomes a union directory consisting of one directory (the new
file).
Sys->MBEFORE
Both the old and new files must be directories. Add the con‐
stituent files of the new directory to the union directory at
old so its contents appear first in the union. After a
Sys->MBEFORE bind or mount, the new directory will be searched
first when evaluating file names in the union directory.
Sys->MAFTER
Like Sys->MBEFORE but the new directory goes at the end of the
union.
In addition, there is a Sys->MCREATE flag that can be OR'd with any of
the above. When a create call (see sys-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 Sys->MCREATE set.
The file is created in that directory; if that attempt fails, the cre‐
ate fails.
With mount, the file descriptor fd must be open for reading and writing
and connected to a file server. After the mount, the file tree start‐
ing at old is served by a kernel mnt(3) device. That device will turn
operations in the tree into messages to the server on fd. Aname
selects among different file trees on the server; the empty (or nil)
string chooses the default tree.
The effects of bind and mount can be undone by unmount. If name is
nil, everything bound to or mounted upon old is unbound or unmounted.
If name is not nil, it is evaluated as described above for bind, and
the effect of binding or mounting that particular result on old is
undone.
SEE ALSOsys-intro(2)DIAGNOSTICS
The return value is a positive integer (a unique sequence number) for
success, -1 for failure.
BUGS
Mount will not return until it has successfully attached to the file
server, so the thread doing a mount cannot be the one serving.
SYS-BIND(2)
