Re: [PATCH RFC 3/8] fs/ext4: Disallow encryption if inode is DAX

[Ira Weiny]

On Wed, Apr 15, 2020 at 12:54:34PM -0700, 'Ira Weiny' wrote:
> On Wed, Apr 15, 2020 at 12:03:07PM -0400, Theodore Y. Ts'o wrote:
> > On Mon, Apr 13, 2020 at 09:00:25PM -0700, ira.weiny@xxxxxxxxx wrote:
 
[snip]

> > 
> > Also note that encrypted files are read/write so we must never allow
> > the combination of ENCRPYT_FL and DAX_FL.  So that may be something
> > where we should teach __ext4_iget() to check for this, and declare the
> > file system as corrupted if it sees this combination.
> 
> ok...

After thinking about this...

Do we really want to declare the FS corrupted?

If so, I think we need to return errors when such a configuration is attempted.
If in the future we have an encrypted mode which can co-exist with DAX (such as
Dan mentioned) we can change this.

FWIW I think we should return errors when such a configuration is attempted but
_not_ declare the FS corrupted.  That allows users to enable this configuration
later if we can figure out how to support it.

> 
> > (For VERITY_FL
> > && DAX_FL that is a combo that we might want to support in the future,
> > so that's probably a case where arguably, we should just ignore the
> > DAX_FL for now.)
> 
> ok...

I think this should work the same.

It looks like VERITY_FL and ENCRYPT_FL are _not_ user modifiable?  Is that
correct?

You said that ENCRPYT_FL is set from the parent directory?  But I'm not seeing
where that occurs?

Similarly I don't see where VERITY_FL is being set either?  :-/

I think to make this work correctly we should restrict setting those flags if
DAX_FL is set and vice versa.  But I'm not finding where to do that.  :-/

Ira

> 
> Ira
>