Re: [PATCH v11 06/10] io_uring: introduce attributes for read/write and PI support

["Martin K. Petersen" <martin.petersen@oracle.com>]

Keith,

>> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
>> index aac9a4f8fa9a..38f0d6b10eaf 100644
>> --- a/include/uapi/linux/io_uring.h
>> +++ b/include/uapi/linux/io_uring.h
>> @@ -98,6 +98,10 @@ struct io_uring_sqe {
>>  			__u64	addr3;
>>  			__u64	__pad2[1];
>>  		};
>> +		struct {
>> +			__u64	attr_ptr; /* pointer to attribute information */
>> +			__u64	attr_type_mask; /* bit mask of attributes */
>> +		};
>
> I can't say I'm a fan of how this turned out. I'm merging up the write
> hint stuff, and these new fields occupy where that 16-bit value was
> initially going. Okay, so I guess I need to just add a new attribute
> flag? That might work if I am only appending exactly one extra attribute
> per SQE, but what if I need both PI and Write Hint? Do the attributes
> need to appear in a strict order?

We'll definitely need to be able to include multiple attributes.

Not sure how the attr_type_mask was intended to work. I guess parsing
attributes based on bit position in the mask would be one option.

The SCSI approach would be for each attribute to have a 4-byte header
with a type and a length so multiple attributes can be described by a
single buffer.

FWIW, I wasn't initially a big fan of having the attrs stored outside of
the sqe but it actually made things a lot cleaner for my use case.

-- 
Martin K. Petersen	Oracle Linux Engineering