[Libguestfs] Two multi-conn questions

Hi Eric, A couple of semi-related multi-conn questions. (1) nbdkit-curl-plugin does not currently advertise multi-conn. However forcing multi-conn makes it faster, eg: $ time nbdkit -r curl https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64... timeout=2000 --run ' nbdcopy --no-extents -p $uri jammy-server-cloudimg-amd64.img ' █ 100% [****************************************] real 1m15.438s user 0m2.513s sys 0m4.063s $ time nbdkit -r curl https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64... --filter=multi-conn multi-conn-mode=unsafe timeout=2000 --run ' nbdcopy --no-extents -p $uri jammy-server-cloudimg-amd64.img ' █ 100% [****************************************] real 0m59.635s user 0m3.010s sys 0m4.538s (Note that this is line speed - wget also takes 59 seconds) I believe that multi-conn should be safe to enable in the curl plugin, certainly if we're in read-only mode (which is the most common case for this plugin). It's probably not safe when operating in read-write mode, because HTTP doesn't have any concept of flushing, but almost no web server supports writing. (2) qemu's NBD client still doesn't seem to support multi-conn. This makes qemu-img convert very slow when reading from nbdkit, as in the example below. (Note the '.img' file on that website is actually a qcow2 file.) $ time nbdkit -r curl https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64... --filter=multi-conn multi-conn-mode=unsafe timeout=2000 --run ' qemu-img convert -W -m 16 -p -f qcow2 $uri -O raw jammy-server-cloudimg-amd64.img.raw ' (100.00/100%) real 3m29.412s user 0m17.856s sys 0m8.218s Since we know from (1) above that copying could go at line speed when multi-conn is enabled, and also that qemu-img convert from the same local file takes only about 2 seconds, it seems like qemu-img convert above could go a lot faster if we allowed multi-conn. Is there any work on adding multi-conn support to qemu's NBD client? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top