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; 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 network connection to a file server ready to receive
Styx 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.
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 directories, or both must not
be directories. Flag can be one of:
Sys->MREPL Replace the old file by the new one. Hence-
forth, an evaluation of old will be translated
to the new file. If they are directories (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 directo-
ries. Add the constituent files of the new
directory to the union directory at old so its
contents appear first in the union. After a
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SYS-BIND(2) SYS-BIND(2)
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 cre-
ated in that directory; if that attempt fails, the create
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 starting 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 dif-
ferent 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 ALSO
sys-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.
If the target directory is not already a union, MBEFORE and
MAFTER are equivalent to MREPL; bind a directory to itself
to create a union if necessary.
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