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Date: Thu, 18 Feb 2016 21:10:21 +0100 From: Rasmus Villemoes <linux@...musvillemoes.dk> To: Al Viro <viro@...IV.linux.org.uk> Cc: Jeff Layton <jlayton@...chiereds.net>, "J. Bruce Fields" <bfields@...ldses.org>, Linus Torvalds <torvalds@...ux-foundation.org>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/2] vfs: make sure struct filename->iname is word-aligned On Tue, Feb 16 2016, Al Viro <viro@...IV.linux.org.uk> wrote: > On Tue, Feb 16, 2016 at 11:49:24PM +0100, Rasmus Villemoes wrote: >> I noticed that offsetof(struct filename, iname) is actually 28 on 64 >> bit platforms, so we always pass an unaligned pointer to >> strncpy_from_user. This is mostly a problem for those 64 bit platforms >> without HAVE_EFFICIENT_UNALIGNED_ACCESS, but even on x86_64, unaligned >> accesses carry a penalty, especially when done in a loop. >> >> Let's try to ensure we always pass an aligned destination pointer to >> strncpy_from_user. I considered making refcnt a long instead of doing >> the union thing, and mostly ended up tossing a coin. > > Why not swap it with the previous field, then? Sure, that would work as well. I don't really care how ->iname is pushed out to offset 32, but I'd like to know if it's worth it. Rasmus
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