linux-kernel - Re: [PATCH 1/3] uio: Allow handling of non page-aligned memory regions

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Message-ID: <87h92tqrbu.fsf@steelpick.2x.cz>
Date:   Thu, 16 Mar 2017 14:33:25 +0100
From:   Michal Sojka <sojkam1@....cvut.cz>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, lisovy@...il.com
Subject: Re: [PATCH 1/3] uio: Allow handling of non page-aligned memory regions

On Thu, Mar 16 2017, Greg KH wrote:
> On Thu, Mar 16, 2017 at 01:45:50PM +0100, Michal Sojka wrote:
>> On Thu, Mar 16 2017, Greg KH wrote:
>> > On Tue, Mar 07, 2017 at 03:09:46PM +0100, Michal Sojka wrote:
>> >> Since commit b65502879556 ("uio: we cannot mmap unaligned page
>> >> contents") addresses and sizes of UIO memory regions must be
>> >> page-aligned. If the address in the BAR register is not page-aligned,
>> >> the mentioned commit forces the UIO driver to round the address down
>> >> to the page size. Then, there is no easy way for user-space to learn
>> >> the offset of the actual memory region within the page, because the
>> >> offset seen in the sysfs is calculated from the rounded address and
>> >> thus it is always zero.
>> >> 
>> >> Fix that problem by including the offset in struct uio_mem. UIO
>> >> drivers can set this field and its value is reported via sysfs.
>> >
>> > It is, where?
>> 
>> /sys/class/uio/uio0/maps/map0/offset
>
> Did you change the Documentation/ABI entry for it?

No, because it seems that UIO is not documented there.

-Michal