On 14/08/2019 13:27, Keith Busch wrote: > On Wed, Aug 14, 2019 at 09:18:22AM -0700, Guilherme G. Piccoli wrote: >> [...]If you can give a rough example I appreciate. > > Sure, start with nvme subsystem A, with host connected to to > controllers, X and Y. > > ctrl X gets instance 0, which you assign to the newly discovered > subsytem > > ctrl Y gets instance 1 > > disconnect ctrl X, which releases instance 0 back to the allocator > Thanks a lot for the example Keith! This is the point I missed, returning the id back to allocator. If we happen to have some IDA in kernel without this property, my idea could work! > connect to a new ctrl Z in new subsystem B: ctrl Z gets the first > available instance, which is now 0, and you assign that name to the new > susbystem, colliding with the sysfs nvme-subsys entries we've created > for subsys A, as well as any namespaces. > >> But given the above statement is a fact, what do you think of trying the >> ctrl->instance first and in case we have duplicity, fallback to >> subsystem ID allocator? > > At the point we assign the subsystem identifier, we're locked into using > that for the namespace names, which may be discovered long before we're > aware the host has multiple connections to the same subsystem. > > I think it'd be better to just completely disassociate any notion of > relationships based on names. The following patch enforces that way of > thinking: > > http://lists.infradead.org/pipermail/linux-nvme/2019-May/024142.html > Interesting thread, thanks for the pointer. I think no matter what we do in this front (to disassociate the relation of nvme numbering), it'll always be confusion, specially since we broke valid assumptions since nvme day-0. Would it be possible of instead reusing the numbering positions in the naming, add more fields? It is a suggestion from my colleague Dan (CCed here), something like: for non-multipath nvme, keep nvmeC and nvmeCnN (C=controller ida, N=namespace); for multipath nvme, use nvmeScCnN (S=subsystem ida). Let me know your thoughts, and thanks again for the prompt response! Cheers, Guilherme
