"Michael S. Tsirkin" <m...@redhat.com> writes: > On Mon, Nov 08, 2010 at 11:32:01AM +0100, Markus Armbruster wrote: >> Ryan Harper <ry...@us.ibm.com> writes: >> >> > * Markus Armbruster <arm...@redhat.com> [2010-11-06 04:19]: >> >> Ryan Harper <ry...@us.ibm.com> writes: >> >> >> >> > * Markus Armbruster <arm...@redhat.com> [2010-11-05 11:11]: >> >> >> Ryan Harper <ry...@us.ibm.com> writes: >> >> >> >> >> >> > * Markus Armbruster <arm...@redhat.com> [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. >> >> > >> >> > OK, drive_del() and as you mentioned, drive_unplug will take out the >> >> > block driver, but doesn't remove the dinfo object; that ends up dying >> >> > when we call the device destructor. I think for symmetry we'll want >> >> > drive_del to remove the dinfo object as well. >> >> >> >> Exactly. >> >> >> >> a. bdrv_detach() to zap the pointer from bdrv to qdev >> >> b. zap the pointer from qdev to bdrv >> >> c. drive_uninit() to dispose of the host part >> > >> > a-c need to be done to match netdev_del symmetry? How hard of a req is >> > this? >> >> Without (c), it's not a delete. And (c) without (b) leaves a dangling >> pointer. (c) without (a) fails an assertion in bdrv_delete(). >> >> Aside: (b) should probably be folded into bdrv_detach(). >> >> >> Step b could be awkward with (3), because you don't know device details. >> >> I guess you have to search device properties for a drive property >> >> pointing to bdrv. I like (1) because it puts that loop in the one place >> >> where it belongs: qdev core. (3) duplicates it in every HOSTDEV_del. >> >> Except for netdev_del, which is special because of VLANs. >> >> >> >> To avoid step b, you could try to keep the bdrv around in a special >> >> zombie state. Still have to free the dinfo, but can't use >> >> drive_uninit() for that then. >> >> >> >> If you think I'm overcomplicating this, feel free to prove me wrong with >> >> working code :) >> > >> > drive_unplug() works as-is today; so it does feel very combursome at >> > this point. Other than the name change and agreement on how mgmt should >> > invoke the command, it's been a long ride to get here. >> >> Sometimes it takes a tough man to make a tender chicken. > >> > I'll take my best shot at trying to clean up the other >> > pointers and objects; though on one of my attempts when I took out the >> > dinfo() object that didn't go so well; going to have to audit who uses >> > dinfo and where and what they check before calling it to have a proper >> > cleanup that doesn't remove the whole device altogether. >> >> Steps a, b, c are the result of my (admittedly quick) audit. >> >> Here's how the various objects are connected to each other: >> >> contains >> drivelist -----------> DriveInfo >> | >> | .bdrv >> | .id == .bdrv->device_name >> | >> contains V >> bdrv_states -----------> BlockDriverState >> | ^ >> .peer | | >> | | host part >> -----------------------------|---|----------------------------------- >> | | guest part >> | | property "drive" >> v | >> DeviceState >> >> To disconnect host from guest part, you need to cut both pointers. To >> delete the host part, you need to delete both objects, BlockDriverState >> and DriveInfo. > > > If we remove DriveInfo, how can management later detect that guest part > was deleted?
Directly: check whether the qdev is gone. I don't know how to check that indirectly, via DriveInfo. > If you want symmetry with netdev, it's possible to keep a > shell of BlockDriverState/DriveInfo around (solving dangling pointer > problems). netdev_del deletes the host network part: (qemu) info network Devices not on any VLAN: net.0: net=10.0.2.0, restricted=n peer=nic.0 nic.0: model=virtio-net-pci,macaddr=52:54:00:12:34:56 peer=net.0 (qemu) netdev_del net.0 (qemu) info network Devices not on any VLAN: nic.0: model=virtio-net-pci,macaddr=52:54:00:12:34:56 peer=net.0 It leaves around the VLAN object. Since qdev property points to that, it doesn't dangle. In my opinion, drive_del should make the drive vanish from "info block", just like netdev_del makes the netdev vanish from "info network". And that means deleting it from bdrv_states. Whether we delete it alltogether (which is what I sketched), or turn it into a zombie is a separate question. Both work for me.