[Libguestfs] [libnbd PATCH 6/7] states: Give up on oversized reply length

[Eric Blake]

On 6/14/19 4:54 PM, Eric Blake wrote:
> Any server that sends a reply to NBD_OPT_* or NBD_CMD_* longer than
> the maximum length we are willing to use for NBD_CMD_{READ,WRITE} is
> probably broken; it is not worth waiting for read() to wait for that
> many bytes to arrive from the server to bring the connection back into
> sync for the next operation, so just declare it dead.
> 
> It may be possible to provoke nbdkit into being such a server when
> replying to NBD_CMD_BLOCK_STATUS on a disk that reports alternating
> extents, but if so, we should patch nbdkit to truncate before sending
> that large of a chunk.

In fact, after an hour of fiddling around, I proved it was possible, and
have since posted/pushed the corresponding nbdkit fix.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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