>>> On 9/14/2015 at 10:03 PM, in message
<caflbxzayaqtejib3rfg8qhxjczqy8bbte0hxj+ft6abslf+...@mail.gmail.com>, George
Dunlap <george.dun...@eu.citrix.com> wrote:
> On Mon, Sep 14, 2015 at 12:12 PM, Ian Jackson <ian.jack...@eu.citrix.com>
> 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
> >
> > 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 ?
>
> libusb is already a published API that supports uint8, or up to 255.
> Following their lead seems like a reasonable thing to do. If ever
> that number goes above 255, basically every Linux program that touches
> a USB device will need to be recompiled with a new version of libusb.
>
> Is there any reason for Linux to go above 255? Things I can think of:
>
> 1. Users have more than 255 devices plugged into the same bus.
>
> 2. A security / confusion issue due to devnum reuse when users plug
> and unplug devices hundreds of times.
>
> Both of these seem pretty unlikely.
>
> I would personally go with uint8, but int16 or int32 certainly won't hurt.
So can we agree to use uint8 for hostbus and hostaddr as libusb does?
>
> -George
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
>
>
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
