From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Jackson <Ian.Jackson@eu.citrix.com>
Subject: Re: [PATCH V6 3/7] libxl: add pvusb API
Date: Mon, 14 Sep 2015 12:12:11 +0100
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To: Juergen Gross <jgross@suse.com>
Cc: Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, George Dunlap <George.Dunlap@eu.citrix.com>, Chun Yan Liu <cyliu@suse.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>, Jim Fehlig <JFEHLIG@suse.com>, Simon Cao <caobosimon@gmail.com>
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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 ?

Ian.