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Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from devic
From: |
Ryan Harper |
Subject: |
Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal |
Date: |
Fri, 29 Oct 2010 10:03:36 -0500 |
User-agent: |
Mutt/1.5.6+20040907i |
* Markus Armbruster <address@hidden> [2010-10-29 09:13]:
> [Note cc: Michael]
>
> Ryan Harper <address@hidden> writes:
>
> > This patch series decouples the detachment of a block device from the
> > removal
> > of the backing pci-device. Removal of a hotplugged pci device requires the
> > guest to respond before qemu tears down the block device. In some cases, the
> > guest may not respond leaving the guest with continued access to the block
> > device.
> >
> > The new monitor command, drive_unplug, will revoke a guests access to the
> > block device independently of the removal of the pci device.
> >
> > The first patch adds a new drive find method, the second patch implements
> > the
> > monitor command and block layer changes.
> >
> > Changes since v3:
> > - Moved QMP command for drive_unplug() to separate patch
> >
> > Changes since v2:
> > - Added QMP command for drive_unplug()
> >
> > Changes since v1:
> > - CodingStyle fixes
> > - Added qemu_aio_flush() to bdrv_unplug()
> >
> > Signed-off-by: Ryan Harper <address@hidden>
>
> If I understand your patch correctly, the difference between your
> drive_unplug and my blockdev_del is as follows:
>
> * drive_unplug forcefully severs the connection between the host part of
> the block device and its BlockDriverState. A shell of the host part
> remains, to be cleaned up later. You need forceful disconnect
> operation to be able to revoke access to an image whether the guest
> cooperates or not. Fair enough.
>
> * blockdev_del deletes a host part. My current version fails when the
> host part is in use. I patterned that after netdev_del, which used to
> work that way, until commit 2ffcb18d:
>
> Make netdev_del delete the netdev even when it's in use
>
> To hot-unplug guest and host part of a network device, you do:
>
> device_del NIC-ID
> netdev_del NETDEV-ID
>
> For PCI devices, device_del merely tells ACPI to unplug the device.
> The device goes away for real only after the guest processed the ACPI
> unplug event.
>
> You have to wait until then (e.g. by polling info pci) before you can
> unplug the netdev. Not good.
>
> Fix by removing the "in use" check from do_netdev_del(). Deleting a
> netdev while it's in use is safe; packets simply get routed to the bit
> bucket.
>
> Isn't this the very same problem that's behind your drive_unplug?
Yes it is.
>
> I'd like to have some consistency among net, block and char device
> commands, i.e. a common set of operations that work the same for all of
> them. Can we agree on such a set?
Yeah; the current trouble (or at least what I perceive to be trouble) is
that in the case where the guest responds to device_del induced ACPI
removal event; the current qdev code already does the host-side device
tear down. Not sure if it is OK to do a blockdev_del() immediately
after the device_del. What happens when we do:
device_del
ACPI to guest
blockdev_del /* removes host-side device */
guest responds to ACPI
qdev calls pci device removal code
qemu attempts to destroy the associated host-side block
That may just work today; and if not, it shouldn't be hard to fix up the
code to check for NULLs
>
> Even if your drive_unplug shouldn't fit in that set, we might want it as
> a stop-gap. Depends on how urgent the need for it is. Yet another
> special-purpose command to be deprecated later.
The fix is urgent; but I'm willing to spin a couple patches if it helps
get this into better shape.
--
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
address@hidden
- Re: [Qemu-devel] [PATCH 2/3] v2 Fix Block Hotplug race with drive_unplug(), (continued)
- Re: [Qemu-devel] [PATCH 2/3] v2 Fix Block Hotplug race with drive_unplug(), Kevin Wolf, 2010/10/29
- Re: [Qemu-devel] [PATCH 2/3] v2 Fix Block Hotplug race with drive_unplug(), Anthony Liguori, 2010/10/29
- Re: [Qemu-devel] [PATCH 2/3] v2 Fix Block Hotplug race with drive_unplug(), Kevin Wolf, 2010/10/29
- Re: [Qemu-devel] [PATCH 2/3] v2 Fix Block Hotplug race with drive_unplug(), Anthony Liguori, 2010/10/29
- Re: [Qemu-devel] [PATCH 2/3] v2 Fix Block Hotplug race with drive_unplug(), Kevin Wolf, 2010/10/29
- Re: [Qemu-devel] [PATCH 2/3] v2 Fix Block Hotplug race with drive_unplug(), Christoph Hellwig, 2010/10/30
- Re: [Qemu-devel] [PATCH 2/3] v2 Fix Block Hotplug race with drive_unplug(), Markus Armbruster, 2010/10/29
[Qemu-devel] [PATCH 1/3] v2 Add drive_get_by_id, Ryan Harper, 2010/10/25
Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal, Markus Armbruster, 2010/10/29
- Re: [Qemu-devel] [PATCH 0/3] v4 Decouple block device removal from device removal,
Ryan Harper <=