Re: [Xen-devel] [PATCH V6 3/7] libxl: add pvusb API

[Juergen Gross <jgross@xxxxxxxx>]

On 09/14/2015 01:12 PM, Ian Jackson wrote:
> Juergen Gross writes ("Re: [Xen-devel] [PATCH V6 3/7] libxl: add pvusb API"):
> > On 09/14/2015 12:36 PM, George Dunlap wrote:
> > > Anyone want to look into the Linux source code to find out how big it
> > > will allow busnum / devnum to grow?
> > drivers/usb/core/hcd.c is using a bitmap to find the next bus number
> > currently not in use. It's size is USB_MAXBUS which in turn has the
> > value 64.
> >
> > choose_devnum() in drivers/usb/core/hub.c is doing a similar job for
> > device numbers. Here the highest number supported is 127.
> We are defining an API, which shouldn't involve this kind of
> implementation-grobbling.
>
> At an API level, it seems that this Linux busnum is not documented to
> have any particular number or behaviour or range or anything.  We
> should use the biggest type we can use conveniently.
Agreed.

> Do we need to worry that some bus might have 2^24 unplugs/plugs
> (perhaps in some kind of software emulation) and that we need to use a
> type which can hold a uint32_t or maybe even a uint64_t ?
uint128_t ? ;-)

I think 24 bits should be more than enough. Nobody will accept such huge
numbers without any need: they are to be used by users.


Juergen


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