Re: [PATCH v7 06/10] io_uring/rw: add support to send metadata along with read/write

[Christoph Hellwig <hch@lst.de>]

On Wed, Nov 06, 2024 at 11:30:45AM +0530, Kanchan Joshi wrote:
> >   1) some space to actually store the extra fields
> >   2) a flag that the additional values are passed
> 
> Yes, this is exactly how the patch is implemented. 'meta-type' is the 
> flag that tells additional values (representing PI info) are passed.
> 
> > any single value is not going to help with supporting arbitrary
> > combinations,
> 
> Not a single value. It is a u16 field, so it can represent 16 possible 
> flags.
> This part in the patch:
> 
> +enum io_uring_sqe_meta_type_bits {
> +       META_TYPE_PI_BIT,
> +       /* not a real meta type; just to make sure that we don't overflow */
> +       META_TYPE_LAST_BIT,
> +};

Well, then it's grossly misnamed and underdocumented.  For one the
meta name simply is wrong because it's about all extra features.
Second a type implies an enumeration of types, not a set of flags.

So if you actually name this extended_features or similar and clearly
document it might actually make sense.