readme

openGFS , a kind of file system.

This is the OpenGFS version of GNBD, the G Network Block Device.

GNBD is a fork of the Linux kernel nbd device.  There are a number of
features that gnbd has over nbd:

Multiple clients per server
  We don't have to worry about two reads or writes overlapping on the server
  as the server opens the block file in syncronous mode, and network receives
  are keep apart with mutexes.  Everything else must be handled by higherlevel
  layers, e.g. the OpenGFS filesystem.

Transparent reconnection.
  The loss of a server does not mean that programs using the device file
  immediatily get errors.  Activity on the device pauses, and remains
  paused until gnbd gets reconnected to a server, and re-issuse any
  unfulfilled requests.

Other proccesses Suspending IO.
  Simply, some other process can come and state that the device should stop
  talking (or trying to talk) to the server.  Think `Entering cluster
  tansition'

Notification of change of server.
  Just change the ip and port of where the device looks for a server.

Resumption of service.
  Connect to the server again, and re-issue any requests that haven't
  gotten replies yet.


Currently gnbd has a kernel thread and a TCP socket for each opened block
device.  If either of these fail, the device is still opened.  This is to
allow modification of some parameters via ioctl.

There is a short and simple userland program to set the ip and port.  Done
with those ioctls.

Server ip and port can also be specified at module load.  This uses the
config option durring insmod. More details in the main.c file.

In case anyone asks.  I have no plans on any sort of block encryption.
Tunneling over ssh work just fine. (I jsut tested it.) So if you feel you
need a secure block server, install and use ssh.

The current server was written in less than an hour to get work on the
kernel module started.  It sucks. (but works)

For all sorts of gory details, scan the source, the comments can be
entertaining.  And possibly informative.