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;

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. 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 directories, 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 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 directories. Add the constituent 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 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 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.