On 12/9/20 10:38 PM, Bart Van Assche wrote:
On 12/7/20 10:55 AM, Palmer Dabbelt wrote:
All in all, I've found it a bit hard to figure out what sort of interest
people
have in dm-user: when I bring this up I seem to run into people who've done
similar things before and are vaguely interested, but certainly nobody is
chomping at the bit. I'm sending it out in this early state to try and
figure
out if it's interesting enough to keep going.
Cc-ing Josef and Mike since their nbd contributions make me wonder
whether this new driver could be useful to their use cases?
Sorry gmail+imap sucks and I can't get my email client to get at the original
thread. However here is my take.
1) The advantages of using dm-user of NBD that you listed aren't actually
problems for NBD. We have NBD working in production where you can hand off the
sockets for the server without ending in timeouts, it was actually the main
reason we wrote our own server so we could use the FD transfer stuff to restart
the server without impacting any clients that had the device in use.
2) The extra copy is a big deal, in fact we already have too many copies in our
existing NBD setup and are actively looking for ways to avoid those.
Don't take this as I don't think dm-user is a good idea, but I think at the very
least it should start with the very best we have to offer, starting with as few
copies as possible.
If you are using it currently in production then cool, there's clearly a usecase
for it. Personally as I get older and grouchier I want less things in the
kernel, so if this enables us to eventually do everything NBD related in
userspace with no performance drop then I'd be down. I don't think you need to
make that your primary goal, but at least polishing this up so it could
potentially be abused in the future would make it more compelling for merging.
Thanks,
Josef
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