io_uring/cmd: introduce IORING_URING_CMD_REISSUE flag

Add a flag IORING_URING_CMD_REISSUE that ->uring_cmd() implementations
can use to tell whether this is the first or subsequent issue of the
uring_cmd. This will allow ->uring_cmd() implementations to store
information in the io_uring_cmd's pdu across issues.

Signed-off-by: Caleb Sander Mateos <[email protected]>
Acked-by: David Sterba <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: calebsander

include/linux/io_uring/cmd.h

@@ -8,6 +8,8 @@
 
 /* only top 8 bits of sqe->uring_cmd_flags for kernel internal use */
 #define IORING_URING_CMD_CANCELABLE	(1U << 30)
+/* io_uring_cmd is being issued again */
+#define IORING_URING_CMD_REISSUE	(1U << 31)
 
 struct io_uring_cmd {
 	struct file	*file;

io_uring/uring_cmd.c

@@ -261,7 +261,11 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
 	}
 
 	ret = file->f_op->uring_cmd(ioucmd, issue_flags);
-	if (ret == -EAGAIN || ret == -EIOCBQUEUED)
+	if (ret == -EAGAIN) {
+		ioucmd->flags |= IORING_URING_CMD_REISSUE;
+		return ret;
+	}
+	if (ret == -EIOCBQUEUED)
 		return ret;
 	if (ret < 0)
 		req_set_fail(req);