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.