[ENBD] ENBD with 2.4.2-kernel

[Peter T. Breuer]

"A month of sundays ago Adrian Turcu wrote:"
> > > Interesting. Let me know of problems. If you write up the
> > > configuration, please let me have a pointer.
> Well, I have some interesting results about my new config :-)
> In a word it's working, but...
> 
> If the client is started before the ENBD server starts, 
> well... my client will never connect to the server which says me in logs :
>  
>  nbd-server: Read returned 0 after select predicted read!

Yes, i know. there have been several complaints. In my current code
I've limited the message to one and sent the loop round again with a
delay.

I need to test it more however.

> and after a while from one server started I can saw a lot (10-12) started
> which will cause the machine to hang-up finally.
> 
> I have a silly question: What I've missed ?
> 
> The server (node2) is started this way:
> 
>  nbd-server 4017 /dev/sdb

Needs a signature, I think.

> and the client (node1):
> 
>  insmod -f $PATH_TO_NBD_DRIVER/nbd.o rahead=20 merge_requests=0 sync_intvl=10
>  nbd-client node2 4017 node2 -b 1024 -t 5 /dev/nda

Looks OK, though I have lately been using the syntax node2:4017 .

> If I'll wait those 15 secs before starting the client (the time need for server start-up)
> everything will goes fine.
> 
> The partition /dev/sdb is 3240376320 Bytes in size (~3GBy) 
> Is it to huge for ENBD ? (Another silly question...)

I think not. I have been exporting a 4GB partition
(an LVM one) on 2.4.0 without noticable problems.

Well, until you get hold of my code with the corrected startup loop in
the C code itself, I think I'd do it with a shell script ... launch a
process that starts the client only when it gets the go ahead from the
server, and loop in a while loop until then. Can you think of a
reliable way? I can think of several, but I don't know which is easiest
or best for you ....

1) client mounts node2:/var/run/subsys/nbd/ by nfs, and stops blocking
 the client launch when a file nbd-server.pid appears there

2) client has an inetd entry for some port that launches nbd-client
  when it gets a ping theer. Limit access to that port to the server.
  Get the server to briefly telnet to that port when it has finished
  launching nbd-server.

3) etc.




Peter