Re: [PATCH v2] fs: replace the ki_complete two integer arguments with a single argument

[Jens Axboe <axboe@kernel.dk>]

On 10/21/21 4:57 AM, Christoph Hellwig wrote:
> On Thu, Oct 21, 2021 at 01:32:19AM -0700, Christoph Hellwig wrote:
>>> @@ -1436,8 +1436,8 @@ static void aio_complete_rw(struct kiocb *kiocb, long res, long res2)
>>>  		file_end_write(kiocb->ki_filp);
>>>  	}
>>>  
>>> -	iocb->ki_res.res = res;
>>> -	iocb->ki_res.res2 = res2;
>>> +	iocb->ki_res.res = res & 0xffffffff;
>>> +	iocb->ki_res.res2 = res >> 32;
>>
>> This needs a big fat comments explaining the historic context.
> 
> Oh, and please use the upper_32_bits / lower_32_bits helpers.

Incremental, are you happy with that comment?

diff --git a/fs/aio.c b/fs/aio.c
index e39c61dccf37..3674abc43788 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1436,8 +1436,14 @@ static void aio_complete_rw(struct kiocb *kiocb, u64 res)
 		file_end_write(kiocb->ki_filp);
 	}
 
-	iocb->ki_res.res = res & 0xffffffff;
-	iocb->ki_res.res2 = res >> 32;
+	/*
+	 * Historically we've only had one real user of res2, the USB
+	 * gadget code, everybody else just passes back zero. As we pass
+	 * 32-bits of value at most for either value, bundle these up and
+	 * pass them in one u64 value.
+	 */
+	iocb->ki_res.res = lower_32_bits(res);
+	iocb->ki_res.res2 = upper_32_bits(res);
 	iocb_put(iocb);
 }
 
-- 
Jens Axboe