linux-kernel - RE: [PATCH 01/10] fs: don't allow kernel reads and writes without iter ops

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Date:   Thu, 27 Aug 2020 15:58:02 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Christoph Hellwig' <hch@....de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 01/10] fs: don't allow kernel reads and writes without
 iter ops

From: Christoph Hellwig
> Sent: 27 August 2020 16:00
> 
> Don't allow calling ->read or ->write with set_fs as a preparation for
> killing off set_fs.  All the instances that we use kernel_read/write on
> are using the iter ops already.
> 
> 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.

Is there a real justification for that?
For system calls supplying both methods makes sense to avoid
the extra code paths for a simple read/write.

Any one stupid enough to make them behave differently gets
what they deserve.

	David

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