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From: =?utf-8?Q?Bj=C3=B8rn_Mork?= <bjorn@mork.no>
To: Alan Stern <stern@rowland.harvard.edu>
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Subject: Re: [PATCH v2] usb: devio: Add ioctl to disallow detaching kernel USB drivers.
Organization: m
References: <Pine.LNX.4.44L0.1601251016490.1849-100000@iolanthe.rowland.org>
Date: Mon, 25 Jan 2016 16:32:14 +0100
In-Reply-To: <Pine.LNX.4.44L0.1601251016490.1849-100000@iolanthe.rowland.org>
	(Alan Stern's message of "Mon, 25 Jan 2016 10:21:21 -0500 (EST)")
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Alan Stern <stern@rowland.harvard.edu> writes:
> On Mon, 25 Jan 2016, Bjørn Mork wrote:
>
>> I don't feel much like an expert here, but I can certainly make up an
>> opinion anyway :)
>> 
>> Since 64bits kernels allow usb devio with interface numbers up to 63, I
>> guess you need __u64 to avoid limiting the range?  Limiting will create
>> all sorts of followup problems, so it's definitely easiest to just go
>> with __u64.
>
> But the Linux USB stack only allows up to 32 interfaces (see
> include/linux/usb.h):
>
> /* this maximum is arbitrary */
> #define USB_MAXINTERFACES	32


Ah, I totally missed that.  Thanks


> So there's no point using a 64-bit value.
>
> On the other hand, this value is supposed to be the same size as 
> ps->ifclaimed, which is used as an argument to clear_bit(), set_bit(), 
> and test_bit().  Those routines require unsigned long.

Maybe the input to these should be clamped to USB_MAXINTERFACES?


Bjørn