Re: [Xen-devel] [PATCH V3 4/6] xl: add pvusb commands

[Juergen Gross <jgross@xxxxxxxx>]

On 05/21/2015 01:11 PM, George Dunlap wrote:
> On 05/21/2015 11:52 AM, Juergen Gross wrote:
> > >   From your description, "xm usb-assignable-list" would list *all* USB
> > > devices on the system which were available to be assigned to a guest.
> > >
> > > "xl pci-assignable-list" does *not* list all PCI devices on a system
> > > which are available to be assigned.  It lists the ones which can be
> > > assigned without the "seize=1" parameter -- the ones you've already done
> > > something with.  It won't tell you about the other devices on the system
> > > which have not yet been assigned to pciback.
> > So "xl pci-assignable-list" is suppressing some of the PCI devices which
> > in theory could be assigned. I don't think this "weird" behaviour should
> > be mimicked by "xl usb-assignable-list".
> That's not really an accurate characterization.  I introduced the
> concept of "assignable" because under xm, you had to manually much about
> in sysfs yourself to assign the device to pciback before attaching it to
> a guest.  So "pci-assignable-add" takes a device and assigns it to
> pciback; "pci-attach" attaches an assignable device to the guest.
> "pci-assignable-list" lists the devices which have been made
> "assignable" under this new definition.
>
> > > Yes, from a pedantic perspective, both will tell you on which devices
> > > you can run "X-attach" without any extra arguments.  But from a
> > > practical perspective, "xm usb-assignable-list" tells you something
> > > practical about the state of devices on the whole system; and "xl
> > > pci-assignable-list" tells you a technical quirk about devices are in a
> > > half-way state between not being assigned and actually being assigned.
> > I can't believe you are suggesting to use "a technical quirk" as a good
> > example for future development. Just because a user interface isn't
> > perfect shouldn't result in other interfaces to behave in the same
> > imperfect way.
> You seem to have missed in my tone that I think "xm usb-assignable-list"
> behavior is more useful.  I said that "xm usb-assignable-list" gave you
> practical information, and I said that "xl pci-assignable-list" gives
> you about a technical quirk.  I also said that "pci-assignable" a state
> half-way in between being assigned and not assigned, which I personally
> think portrays it as rather clunky.
I didn't want to offend you, sorry if you felt that way.

> I never claimed that we should make the new usb-*-list command mimic
> pci-assignable-list.  What I'm responding to is your claim that they do
> similar things, and so implying that it should be OK for them to have
> similar names.  They do not do the similar things, and therefore they
> must not have similar names.
>
> So, as I said in the previous e-mail:
> * I think that it would definitely be useful to have the "xm
> usb-assignable-list" functionality.
> * But we cannot give it the same name as the current "xl
> pci-assignable-list" functionality, since they behave differently
> * I think "assignable" is the best name for what "xm
> usb-assignable-list" does; however,
> * We have existing users to consider; I think choosing a different name
> (like "xl usb-available-list") will have the lowest negative impact on
> existing users.
There might be existing users who know about "xm usb-assignable-list".

OTOH I don't care giving it another name, as long as the functionality
is available.


Juergen


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