Re: [PATCH 2/9] fs/ext4: Disallow verity if inode is DAX

Eric Biggers
2020-05-16T01:49:20Z

On Tue, May 12, 2020 at 10:43:17PM -0700, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> Verity and DAX are incompatible. Changing the DAX mode due to a verity
> flag change is wrong without a corresponding address_space_operations
> update.
>
> Make the 2 options mutually exclusive by returning an error if DAX was
> set first.
>
> (Setting DAX is already disabled if Verity is set first.)
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
> ---
> Changes:
> remove WARN_ON_ONCE
> Add documentation for DAX/Verity exclusivity
> ---
> Documentation/filesystems/ext4/verity.rst | 7 +++++++
> fs/ext4/verity.c | 3 +++
> 2 files changed, 10 insertions(+)
>
> diff --git a/Documentation/filesystems/ext4/verity.rst b/Documentation/filesystems/ext4/verity.rst
> index 3e4c0ee0e068..51ab1aa17e59 100644
> --- a/Documentation/filesystems/ext4/verity.rst
> +++ b/Documentation/filesystems/ext4/verity.rst
> @@ -39,3 +39,10 @@ is encrypted as well as the data itself.
>
> Verity files cannot have blocks allocated past the end of the verity
> metadata.
> +
> +Verity and DAX
> +--------------
> +
> +Verity and DAX are not compatible and attempts to set both of these flags on a
> +file will fail.
> +

If you build the documentation, this shows up as its own subsection
"2.13. Verity and DAX" alongside "2.12. Verity files", which looks odd.
I think you should delete this new subsection header so that this paragraph goes
in the existing "Verity files" subsection.

Also, Documentation/filesystems/fsverity.rst already mentions DAX (similar to
fscrypt.rst). Is it intentional that you added this to the ext4-specific
documentation instead?

- Eric