[Sheepdog] Sheepdog client library

[Chris Webb]

In the spirit of merging dog and sheep, do you think it would also be worth
pulling the sheepdog client code into the sheepdog tree instead of putting
it directly into qemu/block/sheepdog.c?

If sd_open, sd_aio_readv, &c were in a small libsheepdog rather than being
part of qemu, other programs than qemu could easily link to them as well,
such as a simple 'block read/write' tool for testing and perhaps completely
different applications which could make use of a distributed drive image
store. The block/sheepdog.c distributed with qemu would then just be a
little shim linking against libsheepdog and behaving exactly as present.

This might make future sheepdog development a bit easier administratively in
the long term too. If the client and server code are developed together in
the same independent project, changes with client and server can be
committed together, whereas if the client is in qemu separate from sheepdog,
a particular version of the client ends up tied to a particular version of
qemu.

What do you think?

Cheers,

Chris.