linux-ext4 - Re: [PATCH v2 3/3] ext4: reimplement ext4_empty_dir() using is_dirent_block

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Message-ID: <20200408093151.GA30172@quack2.suse.cz>
Date:   Wed, 8 Apr 2020 11:31:51 +0200
From:   Jan Kara <jack@...e.cz>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     Harshad Shirwadkar <harshadshirwadkar@...il.com>,
        Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2 3/3] ext4: reimplement ext4_empty_dir() using
 is_dirent_block_empty

On Tue 07-04-20 11:21:01, Andreas Dilger wrote:
> While looking at this code, I noticed that ext4_empty_dir() considers a
> directory without a "." or ".." entry to be empty.  I see this was changed
> in 64d4ce8923 ("ext4: fix ext4_empty_dir() for directories with holes").
> I can understand that we want to not die on corrupted leaf blocks, but it
> isn't clear to me that it is a good idea to allow deleting an entire
> directory tree if the first block has an error (missing "." or ".." as the
> first and second entries) but is otherwise valid.  There were definitely
> bugs in the past that made "." or ".." not be the first and second entries.

That's a good question. I'd just say that ext4_empty_dir() generally
returns true when there's some problem with the directory. In commit
64d4ce8923 I just followed that convention. This behavior of ext4_empty_dir()
(and empty_dir() before in ext3) dates back at least to the beginning of
git history... I guess we could err on the safer side and disallow
directory deletion if there is any problem with it but I guess there was
some motivation for this behavior in the past? Maybe somebody remembers?

									Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR