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

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Message-ID: <20200829092347.GA8833@lst.de>
Date:   Sat, 29 Aug 2020 11:23:47 +0200
From:   'Christoph Hellwig' <hch@....de>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     '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>,
        "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

On Thu, Aug 27, 2020 at 03:58:02PM +0000, David Laight wrote:
> 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.

Al asked for it as two of our four in-tree instances do have weird
semantics, and we can't change that any more.  And the other two
don't make sense to be used with kernel_read and kernel_write (
(/dev/null and /dev/zero).