Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal

[Markus Armbruster]

Ryan Harper <address@hidden> writes:

> * Markus Armbruster <address@hidden> [2010-11-05 08:28]:
>> I'd be fine with any of these:
>> 
>> 1. A new command "device_disconnet ID" (or similar name) to disconnect
>>    device ID from any host parts.  Nice touch: you don't have to know
>>    about the device's host part(s) to disconnect it.  But it might be
>>    more work than the other two.
>
> This is sort of what netdev_del() and drive_unplug() are today; we're
> just saying sever the connection of this device id.   

No, I have netdev_del as (3).

All three options are "sort of" the same, just different commands with
a common purpose.

> I'd like to rename drive_unplug() to blockdev_del() and call it done.  I
> was looking at libvirt and the right call to netdev_del is already
> in-place; I'd just need to re-spin my block patch to call blockdev_del()
> after invoking device_del() to match what is done for net.

Unless I'm missing something, you can't just rename: your unplug does
not delete the host part.

>> 2. New commands netdev_disconnect, drive_disconnect (or similar names)
>>    to disconnect a host part from a guest device.  Like (1), except you
>>    have to point to the other end of the connection to cut it.
>
> What's the advantage here? We need an additional piece of info (host
> part) in addition to the device id?

That's a disadvantage.

Possible advantage: implementation could be slightly easier than (1),
because you don't have to find the host parts.

>> 3. A new command "drive_del ID" similar to existing netdev_del.  This is
>>    (2) fused with delete.  Conceptual wart: you can't disconnect and
>>    keep the host part around.  Moreover, delete is slightly dangerous,
>>    because it renders any guest device still using the host part
>>    useless.
>
> Hrm, I thought that's what (1) is.

No.

With (1), the argument is a *device* ID, and we disconnect *all* host
parts connected to this device (typically just one).

With (3), the argument is a netdev/drive ID, and disconnect *this* host
part from the peer device.

>                                     Well, either (1) or (3); I'd like to
> rename drive_unplug() to blockdev_del() since they're similar function
> w.r.t removing access to the host resource.  And we can invoke them in
> the same way from libvirt (after doing guest notification, remove
> access).

I'd call it drive_del for now, to match drive_add.

>> Do you need anything else from me to make progress?
>
> I think just an agreement on the approach; shouldn't take more than a
> few hours to respin the qemu and libvirt side.