kernel: trace: blktrace: remove redundent memcpy() in compat_blk_trace_setup()

do_blk_trace_setup() will fully initialize 'buts.name', so can remove
the related memcpy(). And also use BLKTRACE_BDEV_SIZE and ARRAY_SIZE
instead of hard code number '32'.
Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blktrace_api.h

@@ -89,7 +89,7 @@ static inline int blk_trace_init_sysfs(struct device *dev)
 #ifdef CONFIG_COMPAT
 
 struct compat_blk_user_trace_setup {
-	char name[32];
+	char name[BLKTRACE_BDEV_SIZE];
 	u16 act_mask;
 	u32 buf_size;
 	u32 buf_nr;

kernel/trace/blktrace.c

@@ -579,13 +579,12 @@ static int compat_blk_trace_setup(struct request_queue *q, char *name,
 		.end_lba = cbuts.end_lba,
 		.pid = cbuts.pid,
 	};
-	memcpy(&buts.name, &cbuts.name, 32);
 
 	ret = do_blk_trace_setup(q, name, dev, bdev, &buts);
 	if (ret)
 		return ret;
 
-	if (copy_to_user(arg, &buts.name, 32)) {
+	if (copy_to_user(arg, &buts.name, ARRAY_SIZE(buts.name))) {
 		blk_trace_remove(q);
 		return -EFAULT;
 	}