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From: David Laight <David.Laight@ACULAB.COM>
Subject: RE: [PATCH] Adds a new ioctl32 syscall for backwards compatibility
 layers
Date: Sun, 17 Jan 2021 18:31:36 +0000
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To: 'Christoph Hellwig' <hch@lst.de>, Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@kernel.org>, 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>

From: Christoph Hellwig
> Sent: 16 January 2021 09:07
...
> > 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.

The only other real option is to pass the 'syscall type' explicitly
through all the layers into every piece of code that might need it.

So passing it as a 'parameter' that is (probably) current->syscall_type
does make sense.

It might even make sense have separate bits for the required emulations.
So you'd have separate bits for '32bit pointers' and '64bit items 32bit
aligned' (etc).

	David

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