linux-ext4 - Re: [PATCH 3/7] ext2fs: Update allocation info earlier in ext2fs_mkdir() and ext2fs

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Date:   Sat, 7 Mar 2020 19:02:20 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/7] ext2fs: Update allocation info earlier in
 ext2fs_mkdir() and ext2fs_symlink()

On Thu, Feb 13, 2020 at 11:15:58AM +0100, Jan Kara wrote:
> Currently, ext2fs_mkdir() and ext2fs_symlink() update allocation bitmaps
> and other information only close to the end of the function, in
> particular after calling to ext2fs_link(). When ext2fs_link() will
> support indexed directories, it will also need to allocate blocks and
> that would cause filesystem corruption in case allocation info isn't
> properly updated. So make sure ext2fs_mkdir() and ext2fs_symlink()
> update allocation info before calling into ext2fs_link().

I'm not sure why there would be file system corruption if the
allocation information isn't updated until later?  Can you explain more?

One problem with moving the alliocation updates earlier is that in
case of errors, they need to be undone.  To be fair, there are other
missing error handling if there are failures, but this change would
make things worse.

					- Ted