GNU Info

(am-utils.info)Operational Principles

---

Next: Mounting a Volume Prev: Volume Binding Up: Overview

---

Enter node , (file) or (file)node

Operational Principles
======================

   Amd operates by introducing new mount points into the namespace.
These are called "automount" points.  The kernel sees these automount
points as NFS filesystems being served by Amd.  Having attached itself
to the namespace, Amd is now able to control the view the rest of the
system has of those mount points.  RPC calls are received from the
kernel one at a time.

   When a "lookup" call is received Amd checks whether the name is
already known.  If it is not, the required volume is mounted.  A
symbolic link pointing to the volume root is then returned.  Once the
symbolic link is returned, the kernel will send all other requests
direct to the mounted filesystem.

   If a volume is not yet mounted, Amd consults a configuration
"mount-map" corresponding to the automount point.  Amd then makes a
runtime decision on what and where to mount a filesystem based on the
information obtained from the map.

   Amd does not implement all the NFS requests; only those relevant to
name binding such as "lookup", "readlink" and "readdir".  Some other
calls are also implemented but most simply return an error code; for
example "mkdir" always returns "read-only filesystem".