Re: [RFC][PATCH v3 01/10] fs: common implementation of file type

[Phillip Potter <phil@philpotter.co.uk>]

On Wed, Oct 24, 2018 at 09:02:06AM -0400, Theodore Y. Ts'o wrote:
> On Tue, Oct 23, 2018 at 09:19:53PM +0100, Phillip Potter wrote:
> > diff --git a/include/linux/file_type.h b/include/linux/file_type.h
> 
> Shouldn't this be in include/uapi/linux/fs_types.h?
> 
> One of things which must be made crystal clear is these definitions
> MUST NOT ever change.  It would break the Userspace ABI, and would
> break file systems on-disk format.
> 
> It might also be useful to be clear *why* we are making this change in
> the first place.  Code refactorization is good from a code maintenance
> perspective (either to fix bugs, although this code is pretty
> trivial), or to make it easier to make changes in a single central
> place (which MUST NOT) happen, or to make the compiled code more
> compact.
> 
> So some documentation of how much text is actually saved might be
> worthwhile.
> 
> 						- Ted

Dear Ted,

Regarding location of the additional header, thank you for this
suggestion - I will move it.

As for making it extra clear that the definitions must not change, I
will add this to the comment at the beginning of the file, and also
in the intro message of the new series I am about to publish.

I can't speak for Amir, but regarding why I think this would be a
good change, my thought process is that it would make adding new
file systems that use these on-disk type layouts in future more
easy, as the central generic implementation can be used rather than
copying and pasting and changing names etc. as needed, which is
more error prone. I am happy to add more documentation in this regard,
and also mention savings where appropriate.

Regards,
Phil