nbdkit now supports cURL — HTTP, FTP, and SSH connections

nbdkit is a liberally licensed NBD (Network Block Device) server designed to let you connect all sorts of crazy disk images sources (like Amazon, Glance, VMware VDDK) to the universal network protocol for sharing disk images: NBD.

New in nbdkit 1.1.8: cURL support. This lets you turn any HTTP, FTP, TFTP or SSH server that hosts a disk image into an NBD server.

For example:

$ nbdkit -r curl url=http://onuma/scratch/boot.iso

and then you can read the disk image using guestfish, qemu or any other nbd client:

$ guestfish --ro -a nbd://localhost -i

Welcome to guestfish, the guest filesystem shell for
editing virtual machine filesystems and disk images.

Type: 'help' for help on commands
      'man' to read the manual
      'quit' to quit the shell

/dev/sda mounted on /

><fs> _

If you are using a normal SSH server like OpenSSH which supports the SSH File Transfer Protocol (aka SFTP), then you can use SFTP to access images:

$ nbdkit -r curl url=sftp://rjones@localhost/~/fedora-20.img

I’m hoping to enable write support in a future version.

It doesn’t work at the moment because I haven’t worked out how to switch between read (GET) and write (POST) requests in a single cURL handle. Perhaps I need to use two handles? The documentation is confusing.

libguestfs and qemu ssh driver

The qemu ssh block device is now up to version 7 … although sadly not upstream yet.

Nevertheless by applying this patch to libguestfs you can use libguestfs to access remote disks over ssh:

$ export LIBGUESTFS_QEMU=~/d/qemu/qemu.wrapper
$ export LIBGUESTFS_BACKEND=direct
$ ./run ./fish/guestfish

Welcome to guestfish, the libguestfs filesystem interactive shell for
editing virtual machine filesystems.

Type: 'help' for help on commands
      'man' to read the manual
      'quit' to quit the shell

><fs> add /tmp/f17x64.img readonly:true format:raw \
        protocol:ssh server:onuma
><fs> run
 100% ⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧ 00:00
><fs> inspect-os
/dev/vg_f17x64/lv_root
><fs> inspect-get-product-name /dev/vg_f17x64/lv_root
Fedora release 17 (Beefy Miracle)
><fs> list-filesystems
/dev/sda1: ext4
/dev/vg_f17x64/lv_root: ext4
/dev/vg_f17x64/lv_swap: swap
><fs> mount /dev/vg_f17x64/lv_root /
><fs> cat /etc/redhat-release
Fedora release 17 (Beefy Miracle)

Everything just works as if this were a local disk.

There are a couple of minor caveats (the major caveat being none of this is upstream): Firstly you have to have ssh-agent set up. Secondly the remote host must be in your known_hosts file (if not, do ssh remotehost first to add it).