[Libguestfs] [PATCH libnbd v2 0/3] copy: Use preferred block size for copying

This is not really an evolution of the previous patch set, I started almost from scratch, but for reference version 1 was here: https://listman.redhat.com/archives/libguestfs/2022-June/029301.html This version does appear to work, all tests pass, and I ran the nbdkit test suite as well (which uses nbdcopy in a bunch of places) and that passes also. Note that patch 3 is a generic fix of a test which was previously broken, but now that larger requests are being made by default, it breaks much more often. Rich.