Re: [Qemu-devel] RFC: QMP event notification for disk media eject

[Markus Armbruster <armbru@redhat.com>]

Luiz Capitulino <lcapitulino@redhat.com> writes:

> Hi there,
>
> I need feedback on a new QMP event.
>
> Problem
> =======
>
> There's no way for a management tool to detect that a guest OS has ejected the
> media in a CDROM or Floppy disk drive (I'm discarding polling, because it's
> undesirable at best).
>
> The end result is that the management tool can get confused, this is happening
> with libvirt when migration is involved: if the guest is saved/restored or
> migrated, then libvirt will start the guest again with media still present.
>
> NOTE: Most of the analysis here was done by Daniel Berrange.
>
> Solution
> ========
>
> We need a new QMP event to solve that. There are two possible events, a
> general one and a very specific one.
>
> There are 3 scenarios in which both events should be emitted:
>
>  1. When guest OS ejects media
>  2. When 'eject' monitor command is run
>  3. When 'change' monitor command is run
>
> BLOCK_MEDIA_CHANGE
> ------------------
>
> This is the general event, it's emitted when any removable block device
> is changed.
>
> Ideally, the event should contain two pieces of info:
>
>  - qdev device name
>  - new file path (to allow distinguishing eject from change)
>
> Example:
>
>   { "event": "BLOCK_MEDIA_CHANGE", "data": { "qdev-id": "myid",
>                                              "new-path": "/foo/bar/dir/distro.iso" },
>                                              ... }

What if a host block device that isn't currently connected to a qdev
goes through a media change?

What if the connected qdev doesn't have an ID?

> BLOCK_MEDIA_EJECT
> -----------------
>
> This event is only emitted when a CDROM or a floppy disk is ejected.
>
> The event contains one info one:
>
>  - device name
>
> Example:
>
>   { "event": "BLOCK_MEDIA_EJECT", "data": { "device-name": "ide1-cd0" }, ... }

What makes CD-ROM and floppy special?