Andy's Portable NBD Server
July 13, 2004
adi@hexapodia.org

This is a POSIX implementation of a server for the Linux Network Block
Device (nbd).  It has been tested on OpenBSD/x86 3.4 with a Linux/x86
2.4.25 client using nbd 2.7.1 from nbd.sourceforge.net.  nbd-2.7.1
includes a client, but that client only compiles on Linux; this 'nbdsvr'
is designed to run on any POSIX system supporting 'long long'.

nbdsvr can be used to serve blocks from a regular file, in which case it
can autodetect the length; or blocks from a block device, in which case
the length must be specified on the command line.

Usage:
obsd% sudo disklabel wd1
...
  i: 68372577       63    ext2fs                        # (Cyl.    0*- 67829)
...
obsd% cd nbdsvr-0.1
obsd% make
obsd% sudo ./nbdsvr [-d] 4444 /dev/wd1i $((68372577 * 512))

linux# nbd-client pirx 4444 /dev/nd0
linux# mount /dev/nd0 /mnt/tmp
linux# ls /mnt/tmp
...
linux# umount /mnt/tmp
linux# nbd-client -d /dev/nd0

Pass multiple -d options to nbdsvr to get more verbose debugging output.


TODO:
1.  Test on a variety of client and server platforms (32be, 64le, 64be)
2.  Use mmap(2) rather than lseek(2)/read(2)/write(2) for I/O
3.  Use mincore(2) and I/O helper processes to do async I/O and service
    requests out of order
4.  Statistics including average request latency, bandwidth, etc.

BLUE SKY:
5.  Extend nbd protocol for authentication, privacy, and data integrity
    (Possibly leverage IPSec for privacy and integrity)
6.  Clients for non-Linux platforms