On Fri, Jul 10, 2020 at 7:21 PM Matthew Wilcox [off-list ref] wrote:

On Fri, Jul 10, 2020 at 02:49:32PM +0100, Christoph Hellwig wrote:

quoted

On Fri, Jul 10, 2020 at 02:48:24PM +0100, Matthew Wilcox wrote:

quoted

If we're going to go the route of changing the CQE, how about:

 struct io_uring_cqe {
         __u64   user_data;      /* sqe->data submission passed back */
-        __s32   res;            /* result code for this event */
-        __u32   flags;
+   union {
+           struct {
+                   __s32   res;            /* result code for this event */
+                   __u32   flags;
+           };
+           __s64   res64;
+   };
 };

then we don't need to change the CQE size and it just depends on the SQE
whether the CQE for it uses res+flags or res64.

How do you return a status code or short write when you just have
a u64 that is needed for the offset?

it's an s64 not a u64 so you can return a negative errno.  i didn't
think we allowed short writes for objects-which-have-a-pos.

If we are doing this for zone-append (and not general cases), "__s64
res64" should work -.
64 bits = 1 (sign) + 23 (bytes-copied: cqe->res) + 40
(written-location: chunk_sector bytes limit)

-- 
Joshi