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

[Marcel Apfelbaum]

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. 

> 
> 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".

> 
> 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".

> 
> 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.

> Why is usb-tablet DEVICE_CATEGORY_MISC, but usb-wacom-tablet
> DEVICE_CATEGORY_INPUT?
This is a bug. Thanks for catching it!

> 
> 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".

> 
> 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.

> 
> 
> 
> [*] I hate that.