linux-kernel - Re: fs: layered device driver to write to evdev

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Message-ID: <CABDcavbv5=54Hv4_TRgAiQK9fvXHbpy3O288Lc5pfO2Q+8Y=SA@mail.gmail.com>
Date:   Thu, 3 Nov 2022 09:22:35 +0100
From:   Guillermo Rodriguez Garcia <guille.rodriguez@...il.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>
Subject: Re: fs: layered device driver to write to evdev

El jue, 3 nov 2022 a las 1:04, Luis Chamberlain (<mcgrof@...nel.org>) escribió:
>
> On Wed, Nov 02, 2022 at 02:14:24PM +0100, Guillermo Rodriguez Garcia wrote:
> > I understand that device drivers should implement ->write_iter if they
> > need to be written from kernel space, but evdev does not support this.
> > What is the recommended way to have a layered device driver that can
> > talk to evdev ?
>
> Shouldn't just writing write_iter support make this work?

If I understand correctly, supporting both write and write_iter is not
allowed [1]:

"If a file has both the regular ->read/->write methods and the iter
variants those could have different semantics for messed up enough
drivers.  Also fails the kernel access to them in that case."

 [1]: https://lore.kernel.org/all/20200817073212.830069-3-hch@lst.de/

Thanks,

Guillermo Rodriguez Garcia
guille.rodriguez@...il.com