srv – server registry

bind –c #s$srvspec /srv

The srv device provides a tree of directories holding already–open channels to services. In effect, srv is a bulletin board on which processes may post open file descriptors to make them available to other processes.

To install a channel, create a new file such as /srv/myserv and then write a text string (suitable for strtoul; see atof(2)) giving the file descriptor number of an open file. Any process may then open /srv/myserv to acquire another reference to the open file that was registered.

An entry in srv holds a reference to the associated file even if no process has the file open. Removing the file from /srv releases that reference.

It is an error to write more than one number into a server file, or to create a file with a name that is already being used.

Opening the clone file allocates a new service directory. Reading clone returns the id of the new directory. This new service directory can then be accessed at /srv/id. Directories are recursive; each new service directory contains its own clone file and sub–directories. Directories can be walked from the root such as #s/id1/id2/id3 which makes them globally addressable. As a convention, /lib/namespace accepts the path to the service directory from the environment variable $srvspec, making it possible to start a new namespace using a specific service directory as a starting point.

To drop one end of a pipe into /srv, that is, to create a named pipe:
int fd, p[2];
char buf[32];
fd = create("/srv/namedpipe", OWRITE, 0666);
fprint(fd, "%d", p[0]);
fprint(p[1], "hello");

At this point, any process may open and read /srv/namedpipe to receive the hello string. Data written to /srv/namedpipe can be received by executing
read(p[1], buf, sizeof buf);

in the above process.

Create a disposable /srv and start a factotum(4) and a rio(1) in it.
<[3=]@{ # close the clone fd
rfork n
bind –c /srv/$id /srv
auth/factotum –s factotum