Re: [PATCH] ext4: fix dir_nlink behaviour

[Theodore Ts'o <tytso@mit.edu>]

On Fri, Jul 21, 2017 at 04:49:27PM -0600, Andreas Dilger wrote:
> The dir_nlink feature has been enabled by default for new ext4
> filesystems since e2fsprogs-1.41 in 2008, and was automatically
> enabled by the kernel for older ext4 filesystems since the
> dir_nlink feature was added with ext4 in kernel 2.6.28+ when
> the subdirectory count exceeded EXT4_LINK_MAX.
> 
> We shouldn't really be enabling filesystem features automatically,
> as this prevents the administrator from disabling the feature at
> format time, or via tune2fs.  This should not affect many users by
> this point, but allows limiting subdirectory counts to those that
> can strictly fit into i_links_count rather than using "1" to
> indicate that the number of links on the directory is not tracked.
> This avoids a bug in glibc fts_read() that incorrectly optimizes
> the directory traversal for such directories.
> 
> This also addresses a minor bug in ext4_inc_count() where i_nlinks
> was wrapped at (EXT4_LINK_MAX - 1) links rather than allowing the
> full EXT4_LINK_MAX links on the parent directory (including "."
> and "..") before storing i_links_count = 1.
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196405
> Signed-off-by: Andreas Dilger <adilger@dilger.ca>

Thanks, applied.

					- Ted