linux-kernel - Re: [PATCH] Adds a new ioctl32 syscall for backwards compatibility layers

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Date:   Sat, 16 Jan 2021 10:07:21 +0100
From:   Christoph Hellwig <hch@....de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Arnd Bergmann <arnd@...nel.org>, Christoph Hellwig <hch@....de>,
        Ryan Houdek <sonicadvance1@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Minchan Kim <minchan@...nel.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Amanieu d'Antras <amanieu@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Xiaoming Ni <nixiaoming@...wei.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Joe Perches <joe@...ches.com>, Jan Kara <jack@...e.cz>,
        David Rientjes <rientjes@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] Adds a new ioctl32 syscall for backwards compatibility
 layers

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.