io_uring: expose read/write attribute capability

After commit 9a213d3b80c0, we can pass additional attributes along with
read/write. However, userspace doesn't know that. Add a new feature flag
IORING_FEAT_RW_ATTR, to notify the userspace that the kernel has this
ability.

Signed-off-by: Anuj Gupta <[email protected]>
Reviewed-by: Li Zetao <[email protected]>
Reviewed-by: Martin K. Petersen <[email protected]>
Tested-by: Martin K. Petersen <[email protected]>
Reviewed-by: Pavel Begunkov <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Anuj Gupta

include/uapi/linux/io_uring.h

@@ -577,6 +577,7 @@ struct io_uring_params {
 #define IORING_FEAT_REG_REG_RING	(1U << 13)
 #define IORING_FEAT_RECVSEND_BUNDLE	(1U << 14)
 #define IORING_FEAT_MIN_TIMEOUT		(1U << 15)
+#define IORING_FEAT_RW_ATTR		(1U << 16)
 
 /*
  * io_uring_register(2) opcodes and arguments

io_uring/io_uring.c

@@ -3713,7 +3713,8 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
 			IORING_FEAT_EXT_ARG | IORING_FEAT_NATIVE_WORKERS |
 			IORING_FEAT_RSRC_TAGS | IORING_FEAT_CQE_SKIP |
 			IORING_FEAT_LINKED_FILE | IORING_FEAT_REG_REG_RING |
-			IORING_FEAT_RECVSEND_BUNDLE | IORING_FEAT_MIN_TIMEOUT;
+			IORING_FEAT_RECVSEND_BUNDLE | IORING_FEAT_MIN_TIMEOUT |
+			IORING_FEAT_RW_ATTR;
 
 	if (copy_to_user(params, p, sizeof(*p))) {
 		ret = -EFAULT;