Re: [PATCH v9 06/11] io_uring: introduce attributes for read/write and PI support

[Pavel Begunkov <asml.silence@gmail.com>]

On 11/16/24 00:00, Pavel Begunkov wrote:
> On 11/14/24 10:45, Anuj Gupta wrote:
>> Add the ability to pass additional attributes along with read/write.
>> Application can populate an array of 'struct io_uring_attr_vec' and pass
>> its address using the SQE field:
>>     __u64    attr_vec_addr;
>>
>> Along with number of attributes using:
>>     __u8    nr_attr_indirect;
>>
>> Overall 16 attributes are allowed and currently one attribute
>> 'ATTR_TYPE_PI' is supported.
> 
> Why only 16? It's possible that might need more, 256 would
> be a safer choice and fits into u8. I don't think you even
> need to commit to a number, it should be ok to add more as
> long as it fits into the given types (u8 above). It can also
> be u16 as well.
> 
>> With PI attribute, userspace can pass following information:
>> - flags: integrity check flags IO_INTEGRITY_CHK_{GUARD/APPTAG/REFTAG}
>> - len: length of PI/metadata buffer
>> - addr: address of metadata buffer
>> - seed: seed value for reftag remapping
>> - app_tag: application defined 16b value
> 
> In terms of flexibility I like it apart from small nits,
> but the double indirection could be a bit inefficient,
> this thing:
> 
> struct pi_attr pi = {};
> attr_array = { &pi, ... };
> sqe->attr_addr = attr_array;

We can also reuse your idea from your previous iterations and
use the bitmap to list all attributes. Then preamble and
the explicit attr_type field are not needed, type checking
in the loop is removed and packing is better. And just
by looking at the map we can calculate the size of the
array and remove all size checks in the loop.

-- 
Pavel Begunkov