linux-kernel - Re: [RFC][PATCHSET v3] non-recursive pathname resolution & RCU symlinks

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Date:	Fri, 15 May 2015 02:26:45 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Jeremy Allison <jra@...ba.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Neil Brown <neilb@...e.de>
Subject: Re: [RFC][PATCHSET v3] non-recursive pathname resolution & RCU
 symlinks

On Thu, May 14, 2015 at 05:25:39PM -0700, Linus Torvalds wrote:

> We can easily make things per-operation, by adding another flag. We
> already have per-operation flags like LOOKUP_FOLLOW, which decides if
> we follow the last symlink or not. We could add a LOOKUP_ICASE, which
> decides whether we compare case or not. Obviously, we'd have to ad the
> proper O_ICASE for open (and AT_ICASE for fstatat() and friends).
> Exactly like we do for LOOKUP_FOLLOW.

> Btw, don't get me wrong. I'm not saying it's a great idea. I think
> icase compares are stupid. Really really stupid. But samba might be
> worth jumping though a few hoops for. The real problem is that even
> with just ASCII, it does make it much easier to create nasty hash
> collisions in the dentry hashes (same hash from 256 variations of
> aAaAAaaA - just repeat the same letter in different variations of
> lower/upper case).

Hold on.  Should
	stat("blah", &buf)	=> ENOENT, OK, let's create it
	mkdir("blah", 0) 	=> EEXIST, bugger, looks like a race
	stat("blah", &buf)	=> ENOENT, Whiskey, Tango, Foxtrot
be possible?  No per-operation flags passed, doesn't even know of the
case-insensitive crap.  And if fstatat() without your new flag would
find c-i matches, then what does that flag do?

Confused...
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