Re: Some comments on using qemu-storage-daemon

[Daniel P . Berrangé]

On Wed, Sep 30, 2020 at 09:40:59AM +0100, Richard W.M. Jones wrote:
> I understand that QSD is at an early stage of development and I'm sure
> you have plans to fix these things.  Nevertheless here are my comments
> after trying to add an interop test with libnbd.
> 
> (1) Documentation!  (Or complete lack of it ...)  I had to ask Kevin
> how to construct the command line because several things were not
> obvious.  In particular the --blockdev parameters only make sense if
> you're already used to constructing blockdev parameters (and these
> are, separately, not well-documented).  And you have to supply the
> parameters in a particular order on the command line, else it doesn't
> work.
> 
> (2) There seems to be no --pid-file option, so there's no way of
> knowing when the server is ready to accept connections, except to
> start QSD and then "sleep for a bit".

It supports QMP via the normal chardev framework, so you can pre-create
a UNIX listener socket and pass in the pre-opened FD. The parent just
sends the QMP handshake, and waits until it gets EOF (exited during
startup) or gets the QMP response (successfully running).

> 
> (3) Seems to be no support for either serving requests over
> stdin/stdout (qemu-nbd also lacks this, but it's common for other NBD
> servers); or for systemd socket activation (qemu-nbd supports this).
> 
> (4) Some parameter names changed between 5.1 and upstream.  I
> understand that you're still finalizing the command line, so this
> isn't a problem in itself, but others who try to use QSD will need to
> be aware of it.


Regards,
Daniel
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