linux-kernel - Re: [PATCH] x86: use compat version for preadv2 and pwritev2

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Date:	Thu, 12 May 2016 09:31:33 +0200
From:	Christoph Hellwig <hch@....de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Dmitry V. Levin" <ldv@...linux.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Christoph Hellwig <hch@....de>,
	LKML <linux-kernel@...r.kernel.org>,
	Milosz Tanski <milosz@...in.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] x86: use compat version for preadv2 and pwritev2

On Wed, May 11, 2016 at 12:14:11PM +0200, Thomas Gleixner wrote:
> On Wed, 11 May 2016, Dmitry V. Levin wrote:
> > Similar to preadv and pwritev, preadv2 and pwritev2 need compat entries
> > in the 32-bit syscall table.
> 
> So this is 2016 and we added a syscalls which require compat support. What's
> wrong here?

Nothing.  It's and extension of readv/writev and uses struct iovec,
which is different for compat vs native.  We have efficient infrastructure
to deal with that in the kernel, while in userspace people would have
to copy around all the iovecs for every I/O, which would be a nightmare.