linux-ext4 - Re: [PATCH] fscrypt: cache decrypted symlink target in ->i

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Date:   Tue, 9 Apr 2019 17:45:54 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH] fscrypt: cache decrypted symlink target in ->i_link

On Wed, Apr 10, 2019 at 01:33:46AM +0100, Al Viro wrote:
> On Tue, Apr 09, 2019 at 04:35:44PM -0700, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@...gle.com>
> > 
> > Path lookups that traverse encrypted symlink(s) are very slow because
> > each encrypted symlink needs to be decrypted each time it's followed.
> > 
> > Make encrypted symlinks faster by caching the decrypted symlink target
> > in ->i_link.  The first call to ->get_link() sets it; later calls simply
> > return it.  ->symlink() also sets it when the symlink is created.
> > 
> > When the inode's ->i_crypt_info is freed, ->i_link is freed too.
> > 
> > Note: RCU-delayed freeing of ->i_link is not yet implemented.
> > Therefore, for now even when ->i_link is set, path lookups must continue
> > to drop out of RCU-walk mode when following an encrypted symlink.
> 
> And how the devil would they continue to do that, if I might ask?
> ->get_link() is *NOT* called if ->i_link is non-NULL, period.

You're right, I didn't notice that ->get_link() isn't called when
->i_link is non-NULL.

But that being the case, what's the point of simple_get_link()?

- Eric