I view uring passthru somewhat as a different thing than sending SG_IO
ioctls to dm-mpath. But it can be argued otherwise.
BTW, the only consumer of it that I'm aware of commented that he
expects dm-mpath to retry SG_IO when dm-mpath retry for SG_IO submission
was attempted (https://www.spinics.net/lists/dm-devel/msg46924.html).
Yeah. But the point is that if we have a path failure, the kernel
will pick a new path next time anyway, both in dm-mpath and nvme-mpath.
If such a path is available at all.
I still think that there is a problem with the existing semantics for
passthru requests over mpath device nodes.
Again, I think it will actually be cleaner not to expose passthru
devices for mpath at all if we are not going to support retry/failover.
I think they are very useful here. Users of passthrough interface
need to be able to retry anyway, even on non-multipath setups. And
a dumb retry will do the right thing.
I think you are painting a simple picture while this is not the case
necessarily. It is not a dumb retry, because the user needs to determine
if an available path for this particular namespace exists or wait for
one if it doesn't want to do a submit/fail constant loop.
A passthru interface does not mean that the user by definition needs to
understand multipathing, ana/ctrl/ns states/mappings, etc. The user may
just want to be able issue vendor-specific commands to the device.
If the user needs to understand multipathing by definition, he/she has
zero use of a mpath passthru device if it doesn't retry IMO.
