linux-kernel - Re: [RFC][PATCHES] iov

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Message-ID: <20141208184632.GG22149@ZenIV.linux.org.uk>
Date:	Mon, 8 Dec 2014 18:46:34 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [RFC][PATCHES] iov_iter.c rewrite

On Mon, Dec 08, 2014 at 10:37:51AM -0800, Linus Torvalds wrote:

> How about we make "kernel_read()" just clear O_DIRECT? Does that fix
> it to just use copies?

Umm...  clearing O_DIRECT on struct file that might have other references
to it isn't nice, to put it mildly...

Frankly, stopping iov_iter_get_pages() on the first page in vmalloc/module
space looks like the sanest strategy anyway.  We'd get the same behaviour
as we used to, and as for finit_module(2), well... put "fails if given
an O_DIRECT descriptor" and be done with that.

Alternatively, we can really go for
	page = is_vmalloc_or_module_addr(addr) ? vmalloc_to_page(addr)
						: virt_to_page(addr)
	*pages++ = get_page(page);
and have the fucker work.  Stability is up to the caller, of course -
reading into buffer that might get freed (and reused) under you has much
worse problems...
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