Re: [Qemu-devel] [PATCH v4 0/3] qemu-help: improve -device command line help

[Marcel Apfelbaum <marcel.a@redhat.com>]

On Wed, 2013-08-21 at 11:23 +0200, Markus Armbruster wrote:
> Marcel Apfelbaum <marcel.a@redhat.com> writes:
> 
> > On Tue, 2013-08-13 at 11:57 +0200, Markus Armbruster wrote:
> >> This isn't patch review, just a couple of observations and questions.
> >> 
> >> Current use of categories, please correct misunderstandings:
> >> 
> >> * A device can have multiple categories.  Most (all?) devices currently
> >>   have exactly one.
> > All device have only one category for now.
> > This is a preparation for multifunction devices.
> >
> >> 
> >> * -device help shows categories, like this:
> >> 
> >>       name "NAME", bus "BUS", categories "CAT1" "CAT2"...
> >> 
> >> * -device help is sorted by category
> >> 
> >> * -device help shows the device once per category.  If the device has no
> >>   categories, it's not shown at all.
> >> 
> >> Should we require devices to have at least one category?
> > The whole idea of the patch was to help user navigating the command line help.
> > A device category will give a user at least a hint. 
> 
> Understand.
> 
> Devices without category are omitted from help.  That's not good.
> Should we require devices to have at least one category?  Or should we
> change help to show devices without a category?
I prefer to require each device to have a category.
The interesting part is how to enforce it.

> 
> >> Eric, does libvirt still parse -device help?  If yes, can it cope with
> >> the addition of "categories ..."?
> > Also the "old" parsing mechanism would still work, it splits the raw
> > by "," and looks for the key like "name".
> >  
> >> 
> >> A possibly better way to group help by category: instead of adding
> >> categories to each line, add category headlines, like this:
> >> 
> >>     Controller/Bridge/Hub devices:
> >>     name "NAME", bus "BUS"...
> >>     ...
> >>     USB devices:
> >>     name "NAME", bus "BUS"...
> >>     ...
> >>     Storage devices:
> >>     ...
> >> 
> >> This way, showing devices with multiple categories once per category
> >> actually makes sense.
> > You are right. This is a very good "next step".
> 
> I'd love to see a patch from you :)
On my to-do list ...

> 
> >> DEVICE_CATEGORY_STORAGE comprises both storage controller devices
> >> (providing storage buses such as IDE, SCSI) and storage devices
> >> (plugging into such buses).  Some of our devices (*-fdc, virtio-blk)
> >> integrate both in one device model[*].
> > Yes, it does comprises both. It still helps the user that can now
> > grep by this storage category and select from it rather than
> > going on all the help.
> >
> >> 
> >> DEVICE_CATEGORY_USB comprises *only* host controller devices (providing
> >> USB bus(es)), *not* USB devices (plugging into USB bus).  These are
> >> categorized by function instead:
> > The "USB" is used here as a code-name rather than the BUS.
> > It was never my intention to clone the bus type. It is already
> > part of the description.
> >
> >> 
> >> * DEVICE_CATEGORY_BRIDGE: usb-host, usb-hub
> >> 
> >> * DEVICE_CATEGORY_STORAGE: usb-bot, usb-uas, usb-storage
> >> 
> >> * DEVICE_CATEGORY_NETWORK: usb-bt-dongle, usb-net
> >> 
> >> * DEVICE_CATEGORY_INPUT: usb-kbd, usb-ccid, usb-wacom-tablet,
> >>   usb-braille, usb-mouse, usb-serial
> >> 
> >> * DEVICE_CATEGORY_SOUND: usb-audio
> >> 
> >> * DEVICE_CATEGORY_MISC: usb-tablet, usb-redir
> >> 
> >> Should they additionally be DEVICE_CATEGORY_USB?
> > As mentioned earlier, better if not (in my opinion.)
> >
> >> 
> >> Why do we have DEVICE_CATEGORY_USB, but no categories for other buses,
> >> like PCI or ISA?  Devices providing such buses are
> >> DEVICE_CATEGORY_BRIDGE.  Why is USB different?
> > Again, we already have the bus information, I was looking for
> > functional info. "USB" was not used here as a BUS, but like a
> > standalone "function".
> 
> Let me rephrase.  Why do we have a category for devices bridging to a
> USB bus (USB host controllers), but don't have categories for devices
> bridging to other buses?
> 
> Perhaps a possible answer is "because we have so many USB host
> controllers, but usually only few to no user-selectable options for the
> other buses".  Just thinking aloud; I'm not sure it's true.
It is true, it was the exact purpose for it.

> 
> >> Why is usb-host DEVICE_CATEGORY_BRIDGE?
> > The category is named "Controller/Bridge/Hub" at command line
> > I didn't want the name to be too long in the code.
> 
> I can't see how USB host device fits "Controller/Bridge/Hub"...
I am open to suggestions. 
 
> 
> The PCI device passhtrough devices kvm-pci-assign and vfio-pci are both
> DEVICE_CATEGORY_MISC.
Any problem with this? I think the Misc Category is appropriate for them.  

> 
> >> Why is usb-tablet DEVICE_CATEGORY_MISC, but usb-wacom-tablet
> >> DEVICE_CATEGORY_INPUT?
> > This is a bug. Thanks for catching it!
> 
> You're welcome :)
> 
> Will you send a patch?
Sure. Soon enough :)
> 
> >> DEVICE_CATEGORY_INPUT is weird.  Some devices in that category are truly
> >> about input (usb-mouse, usb-kbd), others are at least as often used for
> >> output (serial devices, PIOs)...
> > It makes sense to rename it to "Input/Output".
> 
> Looks like the category comprises what we call character devices.
> Perhaps not the friendliest term for casual users, but we already use it
> in our documentation.
And here is my problem. I (maybe) can infer from "char device" that
it refers to input/output devices, but to expose it to user
it is not user friendly/helpful in any way. The code constant may be
DEVICE_CATEGORY_CHARACTER but we need a more meaningful name for the user.
  
> 
> >> The difference between DEVICE_CATEGORY_INPUT and DEVICE_CATEGORY_MISC
> >> seems unclear (see usb-tablet vs. usb-wacom-tablet above).
> > Putting the bug aside, MISC is the category for devices that does
> > not match a specific category.
> >
> >
> > Thanks for the review Markus!
> > The bottom line is that I wanted to help users in their adventure to form
> > the command line by creating "Categories" that would split the 145 help rows
> > in batches of ~20. In this way the user can first select the desired 
> > category and then choose the device.
> 
> Improvement, very much appreciated.
Thanks

> 
> >> [*] I hate that.