Name resolution and lookup

When you run Qnet, the pathname space of all the nodes in your Qnet network is added to yours. Recall that a pathname is a symbolic name that tells a program where to find a file within the directory hierarchy based at root (/).

The pathname space of remote nodes will appear under the prefix /net (the directory created by the Qnet protocol manager, lsm-qnet.so, by default).

For example, remote node1 would appear as:

/net/node1/dev/socket
/net/node1/dev/ser1
/net/node1/home
/net/node1/bin
...

So with Qnet running, you can now open pathnames (files or managers) on other remote Qnet nodes, just as you open files locally on your own node. This means you can access regular files or manager processes on other Qnet nodes as if they were executing on your local node.

Recall our open() example above. If you wanted to open a serial device on node1 instead of on your local machine, you simply specify the path:

fd = open("/net/node1/dev/ser1", O_RDWR, ...); /* Open a serial device on node1 */

For client-server communications, how does the client know what node descriptor to use for the server?

The client uses the filesystem's pathname space to “look up” the server's address. In the single-machine case, the result of that lookup will be a node descriptor, a process ID, and a channel ID. In the networked case, the results are the same—the only difference will be the value of the node descriptor.