* Michael S. Tsirkin <m...@redhat.com> [2010-11-03 16:46]: > On Wed, Nov 03, 2010 at 03:59:29PM -0500, Ryan Harper wrote: > > * Michael S. Tsirkin <m...@redhat.com> [2010-11-03 13:03]: > > > On Wed, Nov 03, 2010 at 12:29:10PM -0500, Ryan Harper wrote: > > > > * Markus Armbruster <arm...@redhat.com> [2010-11-03 11:42]: > > > > > Ryan Harper <ry...@us.ibm.com> writes: > > > > > > > > > > > * Michael S. Tsirkin <m...@redhat.com> [2010-11-03 02:22]: > > > > > >> On Tue, Nov 02, 2010 at 03:23:38PM -0500, Ryan Harper wrote: > > > > > >> > * Michael S. Tsirkin <m...@redhat.com> [2010-11-02 14:18]: > > > > > >> > > On Tue, Nov 02, 2010 at 02:01:08PM -0500, Ryan Harper wrote: > > > > > >> > > > > > > > I like the idea of disconnect; if part of the > > > > > >> > > > > > > > device_del method was to > > > > > >> > > > > > > > invoke a disconnect method, we could implement that > > > > > >> > > > > > > > for block, net, etc; > > > > > >> > > > > > > > > > > > > >> > > > > > > > I'd think we'd want to send the notification, then > > > > > >> > > > > > > > disconnect. > > > > > >> > > > > > > > Struggling with whether it's worth having some > > > > > >> > > > > > > > reasonable timeout > > > > > >> > > > > > > > between notification and disconnect. > > > > > >> > > > > > > > > > > > >> > > > > > > The problem with this is that it has no analog in real > > > > > >> > > > > > > world. > > > > > >> > > > > > > In real world, you can send some notifications to the > > > > > >> > > > > > > guest, and you can > > > > > >> > > > > > > remove the card. Tying them together is what created > > > > > >> > > > > > > the problem in the > > > > > >> > > > > > > first place. > > > > > >> > > > > > > > > > > > >> > > > > > > Timeouts can be implemented by management, maybe with > > > > > >> > > > > > > a nice dialog > > > > > >> > > > > > > being shown to the user. > > > > > >> > > > > > > > > > > >> > > > > > Very true. I'm fine with forcing a disconnect during > > > > > >> > > > > > the removal path > > > > > >> > > > > > prior to notification. Do we want a new disconnect > > > > > >> > > > > > method at the device > > > > > >> > > > > > level (pci)? or just use the existing removal callback > > > > > >> > > > > > and call that > > > > > >> > > > > > during the initial hotremov event? > > > > > >> > > > > > > > > > >> > > > > Not sure what you mean by that, but I don't see a device > > > > > >> > > > > doing anything > > > > > >> > > > > differently wrt surprise or ordered removal. So probably > > > > > >> > > > > the existing > > > > > >> > > > > callback should do. I don't think we need to talk about > > > > > >> > > > > disconnect: > > > > > >> > > > > since we decided we are emulating device removal, let's > > > > > >> > > > > call it > > > > > >> > > > > just that. > > > > > >> > > > > > > > > >> > > > Because current the "removal" process depends on the guest > > > > > >> > > > actually > > > > > >> > > > responding. What I'm suggesting is that, in Marcus's term, > > > > > >> > > > and what > > > > > >> > > > drive_unplug() implements, is to disconnect the host block > > > > > >> > > > device from > > > > > >> > > > the guest device to prevent any further access to it in the > > > > > >> > > > case the > > > > > >> > > > guest doesn't respond to the removal request made via ACPI. > > > > > >> > > > > > > > > >> > > > Very specifically, what we're suggesting instead of the > > > > > >> > > > drive_unplug() > > > > > >> > > > command so to complete the device removal operation without > > > > > >> > > > waiting for > > > > > >> > > > the guest to respond; that's what's going to happen if we > > > > > >> > > > invoke the > > > > > >> > > > response callback; it will appear as if the guest responded > > > > > >> > > > whether it > > > > > >> > > > did or not. > > > > > >> > > > > > > > > >> > > > What I was suggesting above was to instead of calling the > > > > > >> > > > callback for > > > > > >> > > > handing the guest response was to add a device function > > > > > >> > > > called > > > > > >> > > > disconnect which would remove any association of host > > > > > >> > > > resources from > > > > > >> > > > guest resources before we notified the guest. Thinking > > > > > >> > > > about it again > > > > > >> > > > I'm not sure this is useful, but if we're going to remove > > > > > >> > > > the device > > > > > >> > > > without the guests knowledge, I'm not sure how useful > > > > > >> > > > sending the > > > > > >> > > > removal requests via ACPI is in the first place. > > > > > >> > > > > > > > > >> > > > My feeling is that I'd like to have explicit control over > > > > > >> > > > the disconnect > > > > > >> > > > from host resources separate from the device removal *if* > > > > > >> > > > we're going to > > > > > >> > > > retain the guest notification. If we don't care to notify > > > > > >> > > > the guest, > > > > > >> > > > then we can just do device removal without notifying the > > > > > >> > > > guest > > > > > >> > > > and be done with it. > > > > > >> > > > > > > > >> > > I imagine management would typically want to do this: > > > > > >> > > 1. notify guest > > > > > >> > > 2. wait a bit > > > > > >> > > 3. remove device > > > > > >> > > > > > > >> > Yes; but this argues for (1) being a separate command from (3) > > > > > >> > > > > > >> Yes. Long term I think we will want a way to do that. > > > > > >> > > > > > >> > unless we > > > > > >> > require (3) to include (1) and (2) in the qemu implementation. > > > > > >> > > > > > > >> > Currently we implement: > > > > > >> > > > > > > >> > 1. device_del (attempt to remove device) > > > > > >> > 2. notify guest > > > > > >> > 3. if guest responds, remove device > > > > > >> > 4. disconnect host resource from device on destruction > > > > > >> > > > > > > >> > With my drive_unplug patch we do: > > > > > >> > > > > > > >> > 1. disconnect host resource from device > > > > > >> > > > > > >> This is what drive_unplug does, right? > > > > > > > > > > > > Correct. > > > > > > > > > > > >> > > > > > >> > 2. device_del (attempt to remove device) > > > > > >> > 3. notify guest > > > > > >> > 4. if guest responds, remove device > > > > > >> > > > > > > >> > I think we're suggesting to instead do (if we keep disconnect as > > > > > >> > part of > > > > > >> > device_del) > > > > > >> > > > > > > >> > 1. device_del (attemp to remove device) > > > > > >> > 2. notify guest > > > > > >> > 3. invoke device destruction callback resulting in disconnect > > > > > >> > host resource from device > > > > > >> > 4. if guest responds, invoke device destruction path a second > > > > > >> > time. > > > > > >> > > > > > >> By response you mean eject? No, this is not what I was suggesting. > > > > > >> I was really suggesting that your patch is fine :) > > > > > >> Sorry about confusion. > > > > > > > > > > > > I don't mean eject; I mean responding to the ACPI event by writing a > > > > > > response to the PCI chipset which QEMU then in turn will invoke the > > > > > > qdev_unplug() path which ultimately kills the device and the Drive > > > > > > and > > > > > > BlockState objects. > > > > > > > > > > > >> > > > > > >> I was also saying that from what I hear, the pci express support > > > > > >> will at some point need interfaces to > > > > > >> - notify guest about device removal/addition > > > > > >> - get eject from guest > > > > > >> - remove device without talking to guest > > > > > >> - add device without talking to guest > > > > > >> - suppress device deletion on eject > > > > > >> > > > > > >> All this can be generic and can work through express > > > > > >> configuration mechanisms or through acpi for pci. > > > > > >> But this is completely separate from unplugging > > > > > >> the host backend, which should be possible at any point. > > > > > > > > > > > > Yes. I think we've worked out that we do want an independent > > > > > > unplug/disconnect mechanism rather than tying it to device_del. > > > > > > > > > > > > Marcus, it sounds like then you wanted to see a > > > > > > net_unplug/disconnect > > > > > > and that instead of having device_del always succeed and replacing > > > > > > it > > > > > > with a shell, we'd need to provide an explicit command to do the > > > > > > disconnect in a similar fashion to how we're doing drive_unplug? > > > > > > > > > > I'm not sure I parse this. > > > > > > > > You were asking for net and block disconnect to have similar mechanisms. > > > > You mentioned the net fix for suprise removal was to have device_del() > > > > always succeed by replacing the device with a shell/zombie. The > > > > drive_unplug() patch doesn't do the same thing; it doesn't affect the > > > > device_del() path at all, rather it provides mgmt apps a hook to > > > > directly disconnect host resource from guest resource. > > > > > > Yes, the shell thing is just an implementation detail. > > > > ok. What qemu monitor command do I call for net delete to do the > > "disconnect/unplug"? > > > netdev_del
OK. With netdev_del and drive_unplug commands (not sure if we care to change the names to be similar, maybe blockdev_del) in qemu, we can then implement the following in libvirt: 1) detach-device invocation 2) issue device_del to QEMU 2a) notification is sent) 3) issue netdev_del/blockdev_del as appropriate for the device type 4) update guest XML to indicate device has been removed And a fancier version would look like: 1) detach-device invocation 2) issue device_del to QEMU 2a) notification is sent) 3) set a timeout for guest to respond 4) when timeout expires 4a) check if the pci device has been removed by quering QEMU if it hasn't been removed, issue netdev_del/blockdev_del 5) update guest XML to indicate device has been removed in both cases, I think we'll also want a patch that validates that the pci slot is available before handing it out again; this will handle the case where the guest doesn't respond to the device removal request; our net/blockdev_del command will break the host/guest association, but we don't want to attempt to attach a device to the same slot. Marcus, do you think we're at a point where the mechanisms for explicitly revoking access to the host resource is consistent between net and block? If so, then I suppose I might have a consmetic patch to fix up the monitor command name to line up with the netdev_del. -- Ryan Harper Software Engineer; Linux Technology Center IBM Corp., Austin, Tx ry...@us.ibm.com