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

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Date:   Wed, 10 Apr 2019 01:33:46 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Eric Biggers <ebiggers@...nel.org>
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 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.