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Date: Sat, 16 Jan 2021 10:07:21 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] Adds a new ioctl32 syscall for backwards compatibility
 layers
Message-ID: <20210116090721.GA30277@lst.de>
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To: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@kernel.org>, Christoph Hellwig <hch@lst.de>, Ryan Houdek <sonicadvance1@gmail.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Alexander Viro <viro@zeniv.linux.org.uk>, Arnd Bergmann <arnd@arndb.de>, Christian Brauner <christian.brauner@ubuntu.com>, Andrew Morton <akpm@linux-foundation.org>, Minchan Kim <minchan@kernel.org>, Aleksa Sarai <cyphar@cyphar.com>, Sargun Dhillon <sargun@sargun.me>, Miklos Szeredi <mszeredi@redhat.com>, Vincenzo Frascino <vincenzo.frascino@arm.com>, Amanieu d'Antras <amanieu@gmail.com>, Willem de Bruijn <willemb@google.com>, YueHaibing <yuehaibing@huawei.com>, Xiaoming Ni <nixiaoming@huawei.com>, Heiko Carstens <hca@linux.ibm.com>, "Eric W. Biederman" <ebiederm@xmission.com>, Joe Perches <joe@perches.com>, Jan Kara <jack@suse.cz>, David Rientjes <rientjes@google.com>, Arnaldo Carvalho de Melo <acme@redhat.com>, "David S. Miller" <davem@davemloft.net>, Linux ARM <linux-arm-kernel@lists.infradead.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>, Linux API <linux-api@vger.kernel.org>, linux-arch <linux-arch@vger.kernel.org>

On Fri, Jan 15, 2021 at 04:07:46PM -0800, Andy Lutomirski wrote:
> Finally, I'm not convinced that this patch works correctly.  We have
> in_compat_syscall(), and code that uses it may well be reachable from
> ioctl.

ioctls are the prime user of in_compat_syscall().

> I personally would like to see in_compat_syscall() go away,
> but some other people (Hi, Christoph!) disagree, and usage seems to be
> increasing, not decreasing.

I'm absolutely against it going away.  in_compat_syscall helped to
remove so much crap compared to the explicit compat syscalls.