MFC: r207608, r207614, r212651, r212665

MFC: r207608, r207614, r212651, r212665

Go ahead and merge the work edwin@ on tftpd into the tree.  It is a
lot better than what's in the tree now.  Edwin tested it at a prior
employer, but can't test it today.  I've found that it works a lot
better with the various uboot versions that I've used in my embedded
work.  Here's the pkg-descr from the port that describes the changes:

It all started when we got some new routers, which told me the
following when trying to upload configuration or download images
from it: The TFTP server doesn't support the blocksize option.

My curiousity was triggered, it took me some reading of RFCs and
other documentation to find out what was possible and what could
be done. Was plain TFTP very simple in its handshake, TFTP with
options was kind of messy because of its backwards capability: The
first packet returned could either be an acknowledgement of options,
or the first data packet.

Going through the source code of src/libexec/tftpd and going through
the code of src/usr.bin/tftp showed that there was a lot of duplicate
code, and the addition of options would only increase the amount
of duplicate code. After all, both the client and the server can
act as a sender and receiver.

At the end, it ended up with a nearly complete rewrite of the tftp
client and server. It has been tested against the following TFTP
clients and servers:

- Itself (yay!)
- The standard FreeBSD tftp client and server
- The Fedora Core 6 tftp client and server
- Cisco router tftp client
- Extreme Networks tftp client

It supports the following RFCs:

RFC1350 - THE TFTP PROTOCOL (REVISION 2)
RFC2347 - TFTP Option Extension
RFC2348 - TFTP Blocksize Option
RFC2349 - TFTP Timeout Interval and Transfer Size Options
RFC3617 - Uniform Resource Identifier (URI) Scheme and Applicability
          Statement for the Trivial File Transfer Protocol (TFTP)

It supports the following unofficial TFTP Options as described at
http://www.compuphase.com/tftp.htm:

blksize2 - Block size restricted to powers of 2, excluding protocol headers
rollover - Block counter roll-over (roll back to zero or to one)

From the tftp program point of view the following things are changed:

- New commands: "blocksize", "blocksize2", "rollover" and "options"
- Development features: "debug" and "packetdrop"

If you try this tftp/tftpd implementation, please let me know if
it works (or doesn't work) and against which implementaion so I can
get a list of confirmed working systems.

Author: Edwin Groothuis <edwin@FreeBSD.org>

git-svn-id: svn://svn.freebsd.org/base/stable/8@213038 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f