ubd: untagle discard vs write zeroes not support handling

Discard and Write Zeroes are different operation and implemented
by different fallocate opcodes for ubd.  If one fails the other one
can work and vice versa.

Split the code to disable the operations in ubd_handler to only
disable the operation that actually failed.

Fixes: 50109b5 ("um: Add support for DISCARD in the UBD Driver")
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Reviewed-by: Martin K. Petersen <[email protected]>
Acked-By: Anton Ivanov <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Christoph Hellwig

arch/um/drivers/ubd_kern.c

@@ -449,10 +449,11 @@ static int bulk_req_safe_read(
 
 static void ubd_end_request(struct io_thread_req *io_req)
 {
-	if (io_req->error == BLK_STS_NOTSUPP &&
-	    req_op(io_req->req) == REQ_OP_DISCARD) {
-		blk_queue_max_discard_sectors(io_req->req->q, 0);
-		blk_queue_max_write_zeroes_sectors(io_req->req->q, 0);
+	if (io_req->error == BLK_STS_NOTSUPP) {
+		if (req_op(io_req->req) == REQ_OP_DISCARD)
+			blk_queue_max_discard_sectors(io_req->req->q, 0);
+		else if (req_op(io_req->req) == REQ_OP_WRITE_ZEROES)
+			blk_queue_max_write_zeroes_sectors(io_req->req->q, 0);
 	}
 	blk_mq_end_request(io_req->req, io_req->error);
 	kfree(io_req);