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Re: [et-mgmt-tools] [PATCH 0/3] virt-install: support host device assignment

On Sun, Mar 01, 2009 at 11:41:11PM -0500, Cole Robinson wrote:
> The following patches add support for host device assignment to virtinst
> and virt-install.
> The patches aren't complete, since I'm not entirely sure how managed or
> unmanaged devices coincide with HostDeviceDetach and HostDeviceReset,
> and how this relates to PCI vs. USB. But it shouldn't be a big change
> from what's posted.

If 'managed=yes' then libvirt will automatically detach the device
from the host driver. This is nice & simple, but also nice & easy
to shoot yourself in the foot - don't mix up the PCI id for the NIC
you want to pasthrough with your SATA controller ;-)

If 'managed=no' then libvirt expects that the caller has already ensured
the device is detached from the host before *ALL* attempts to start the
guest, now & in the future. The app can use HostDeviceDetach todo this
but remember it has to be manually run every time, which probably is not
what you want. The more likely case for using managed=no, is if you have
statically assigned the PCI device ID to pcistub.ko in /etc/modprobe.conf
so that is guarenteed detached from the moment you boot.

I'd strongly recommend virt-install only use managed=yes, and don't make
the use pick PCI ids off the list, rather present them with the human
readable vendor and product names. When picking PCI devices you can
also use the node device APIs to query for any other devices which are
children of that PCI device - so if there are 2 identical NICs in the
machine, you can show the user that one is eth0 and the other is eth1
to help them pick the right one.

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