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Re: [Xen-devel] [PATCH] PCI Backend - Late Binding

On Wed, 2006-03-22 at 20:41 +0000, Mark Williamson wrote:
> Ryan,
> This is great news, thanks a lot.

Your welcome! :)

> A couple of comments:
> > slots       - lists all of the PCI slots that
> >               the PCI backend will try to seize
> Stylistically I generally expect sysfs files to only contain one value.  So I 
> would have maybe expected a file per registered slot...  People closer to the 
> kernel community may have a more definitive answer...

I think the intention was to have only values of one type, not
necessarily just one value. For example, the resource attribute on PCI
devices contains a line for every resource associated with that PCI
device. From 'Documentation/filesystems/sysfs.txt':

"Attributes should be ASCII text files, preferably with only one value
per file. It is noted that it may not be efficient to contain only
value per file, so it is socially acceptable to express an array of
values of the same type."

I think the slots file is acceptable, but if not, it can be changed.

> This stuff is super cool.  It's amazingly flexible - better than we ever had 
> before.  Do you think you might be able to integrate the bind / unbind 
> operations into pciif.py in Xend?  That way, users don't need to worry about 
> reassigning device drivers or clearing them up afterwards, they could just 
> (for instance) put the slot number in their config file.  From there it's a 
> fairly small step to imagine a GUI where you just drop a NIC from a list onto 
> a virtual machine config :-)

I'm not 100% sure I understand your suggestion here, but I don't know
that it would be appropriate for xend to automatically unbind a device
from another driver (where it may be in-use) if the user specified it in
the configuration file. I think it would be better to fail and make the
user manually unbind it from the other driver. Although it would
certainly be nice to have the PCI backend automatically pick up a device
that's requested if it's not attached to any other driver (and allow the
user to skip the bind step). I won't make any promises about writing
code to do this as I've got a few other things that I'm working on right
now, but I'll keep it in mind.


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