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

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

Ryan,

This is great news, thanks a lot.

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...

This is really just a nitpick, but the kernel folks are quite picky about what 
they allow into sysfs.

> new_slot    - write the name of a slot here
>               (in 0000:00:00.0 format) to have the PCI
>               Backend seize the device in this slot
> remove_slot - write the name of a slot here to have
>               the PCI Backend no longer try to seize a
>               device in this slot

If you did have a file per slot, you could drop remove_slot and echo "remove" 
into the file (or zero, or have a directory per slot and a "remove" file 
underneath it - you get the idea...).

> Note that writing to new_slot/remove_slot does not actually change
> whether the PCI Backend is actually bound to the device in that slot or
> not. Instead, it tells the PCI backend which slots it should be
> interested in. The sysfs attributes "bind" and "unbind" (which are
> common to all drivers, not just the PCI Backend) must be used to
> actually add or remove a device from the PCI backend driver. Note that
> the syntax for specifying a device to bind and unbind is very strict (do
> not append a newline).

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 :-)

Really cool stuff, anyhow, congratulations.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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