Re: RFC: Automatically making a PCI device assignable in the config file

[George Dunlap <george.dunlap@eu.citrix.com>]

On 10/07/13 14:55, Ian Jackson wrote:
> George Dunlap writes ("Re: [Xen-devel] RFC: Automatically making a PCI device assignable in the config file"):
>> Auto-seizing is fairly dangerous; you could easily accidentally yank out
>> the ethernet card, or even the disk that dom0 is using.  I really think
>> it should have to be enabled on a device-by-device basis.
> I don't think this makes any sense.
>
> In practice you are saying that in order to avoid mistakes, the local
> admin must provide the BDF of the device to be passed through in two
> separate places.

That's not what I had in mind; what I had in mind was something like this:

pci = [ '08:04.1,seize=1' ]

Or alternately:

xl pci-attach h0 08:04.1,seize=1

One could also imagine having something in xl.conf like the following:

pci.autoseize = [ '08:04.1','01:00.0' ]

In this case you wouldn't be simply copy and pasting, because you'd 
probably have different domains handling each device.  But in any case, 
this was just exploring the alternatives -- I don't think that's the 
best thing to do.

> But that doesn't actually help.  If this is all properly documented
> and so forth (ie, if the admin has a smooth experience and doesn't
> trip over having dailed to "seize" the device), they will just
> cut-and-paste the same value into both places in the config.
>
> They will also mutter under their breath to ask why this is
> necessary...

If someone can accidentally type "xl pci-attach 08:04.0" instead of "xl 
pci-attach 08.04.1" and suddenly completely lose their network 
connectivity (or yank their hard drive out), then I think they'll 
appreciate it.

In any case, at the moment it's much worse: you have to either 
scriptwise run "xl pci-assignable-add" a device, or add an exclusion on 
the Linux commandline in grub.  So far I'm the only person I know who 
has complained about it. :-)

  -George