When I took over maintenance of the nbd userland utilities, I decided not to do a full rewrite, even though that might have been a good idea. I've managed to keep things running, but the code isn't very pretty. Unfortunately I've also made a few mistakes. Yes, I know. No, I can't say it won't happen again.
Still, the "design", for lack of a better word, of the nbd-server code was problematic, to the extent that some needed performance improvements could not be done, or would require so much work that it would be better to just throw everything out and start over. The unfortunate result of this has been that those who did want to try to do something new with NBD did just that, rather than contributing back to the reference implementation.
Over the years, I've sometimes tried to come up with ways to improve the way in which things work. Most of these efforts haven't gone very far, either because they turned out to be dead ends, or because I just didn't have the time to finish it, and that by the time I could finally work on the branch again, the main branch had diverged so much that the branch was so outdated that I would almost have to start over if I was ever going to make it useful again.
The most recent of those efforts is the io_transaction branch. This
branch has two main goals:
- Make nbd-server somewhat more modular, so that it would be possible to a different backend per export, if necessary
- Improve upon the way we handle select() and friends, so that the server can deal with requests more efficiently.
Today, I've reached the (fairly significant) milestone with that branch that on my machine, it seems to pass the "read" part of the test suite. What's more, the second part of the above two means it actually did so at a much higher speed than it does, on average, on the main branch.
Of course, reading is only half of the story, and no, write doesn't seem to work yet. After that, there's also a lot of work still to be done if I want to get this branch "on par" with the main branch, feature-wise.
But there's a light at the end of the tunnel. Finally.