> Blocking within one, with those locks acquired, and thunking back down to userspace, would mean that 1. a CPU core, and 2. the filesystem itself, would both be tied up indefinitely until that callback thunk returns. If it ever does!
In this theoretical design, you could just block all other administrative modifications. I don't think you need to tie up an entire CPU core, and I'm fairly sure that these zfs operations don't block regular reads and writes.
I think you had it right in your initial comment. There's no good way express branching with an implementation which incrementally submits operations to be committed as a batch. You'd have to take an admin lock on an entire zpool.
EDIT: talked to a zfs dev, said this would take the txg sync lock.
In this theoretical design, you could just block all other administrative modifications. I don't think you need to tie up an entire CPU core, and I'm fairly sure that these zfs operations don't block regular reads and writes.
I think you had it right in your initial comment. There's no good way express branching with an implementation which incrementally submits operations to be committed as a batch. You'd have to take an admin lock on an entire zpool.
EDIT: talked to a zfs dev, said this would take the txg sync lock.