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

From: Al Viro
Date: Thu May 14 2015 - 21:26:57 EST

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?

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