blktrace: split do_blk_trace_setup into two functions

Split do_blk_trace_setup into two functions, this is done to prepare for
an incoming new BLKTRACESETUP2 ioctl(2) which can receive extended
parameters from user-space.

Also move the size verification logic to the callers in preparation for
using a new internal structure later.

Reviewed-by: Damien Le Moal <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Martin K. Petersen <[e-mail]>
Signed-off-by: Johannes Thumshirn <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

kernel/trace/blktrace.c

···
 /*
  * Setup everything required to start tracing
  */
-static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
-			      struct block_device *bdev,
-			      struct blk_user_trace_setup *buts)
+static struct blk_trace *blk_trace_setup_prepare(struct request_queue *q,
+						 char *name, dev_t dev,
+						 u32 buf_size, u32 buf_nr,
+						 struct block_device *bdev)
 {
 	struct blk_trace *bt = NULL;
 	struct dentry *dir = NULL;
···
 
 	lockdep_assert_held(&q->debugfs_mutex);
 
-	if (!buts->buf_size || !buts->buf_nr)
-		return -EINVAL;
-
-	strscpy_pad(buts->name, name, BLKTRACE_BDEV_SIZE);
-
-	/*
-	 * some device names have larger paths - convert the slashes
-	 * to underscores for this to work as expected
-	 */
-	strreplace(buts->name, '/', '_');
-
 	/*
 	 * bdev can be NULL, as with scsi-generic, this is a helpful as
 	 * we can be.
 	 */
 	if (rcu_dereference_protected(q->blk_trace,
 				      lockdep_is_held(&q->debugfs_mutex))) {
-		pr_warn("Concurrent blktraces are not allowed on %s\n",
-			buts->name);
-		return -EBUSY;
+		pr_warn("Concurrent blktraces are not allowed on %s\n", name);
+		return ERR_PTR(-EBUSY);
 	}
 
 	bt = kzalloc(sizeof(*bt), GFP_KERNEL);
 	if (!bt)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	ret = -ENOMEM;
 	bt->sequence = alloc_percpu(unsigned long);
···
 	if (bdev && !bdev_is_partition(bdev))
 		dir = q->debugfs_dir;
 	else
-		bt->dir = dir = debugfs_create_dir(buts->name, blk_debugfs_root);
+		bt->dir = dir = debugfs_create_dir(name, blk_debugfs_root);
 
 	/*
 	 * As blktrace relies on debugfs for its interface the debugfs directory
···
 	 * files or directories.
 	 */
 	if (IS_ERR_OR_NULL(dir)) {
-		pr_warn("debugfs_dir not present for %s so skipping\n",
-			buts->name);
+		pr_warn("debugfs_dir not present for %s so skipping\n", name);
 		ret = -ENOENT;
 		goto err;
 	}
···
 	debugfs_create_file("dropped", 0444, dir, bt, &blk_dropped_fops);
 	debugfs_create_file("msg", 0222, dir, bt, &blk_msg_fops);
 
-	bt->rchan = relay_open("trace", dir, buts->buf_size,
-				buts->buf_nr, &blk_relay_callbacks, bt);
+	bt->rchan = relay_open("trace", dir, buf_size, buf_nr,
+			       &blk_relay_callbacks, bt);
 	if (!bt->rchan)
 		goto err;
+
+	blk_trace_setup_lba(bt, bdev);
+
+	return bt;
+
+err:
+	blk_trace_free(q, bt);
+
+	return ERR_PTR(ret);
+}
+
+static void blk_trace_setup_finalize(struct request_queue *q,
+				     char *name, struct blk_trace *bt,
+				     struct blk_user_trace_setup *buts)
+
+{
+	strscpy_pad(buts->name, name, BLKTRACE_BDEV_SIZE);
+
+	/*
+	 * some device names have larger paths - convert the slashes
+	 * to underscores for this to work as expected
+	 */
+	strreplace(buts->name, '/', '_');
 
 	bt->act_mask = buts->act_mask;
 	if (!bt->act_mask)
 		bt->act_mask = (u16) -1;
-
-	blk_trace_setup_lba(bt, bdev);
 
 	/* overwrite with user settings */
 	if (buts->start_lba)
···
 
 	rcu_assign_pointer(q->blk_trace, bt);
 	get_probe_ref();
-
-	ret = 0;
-err:
-	if (ret)
-		blk_trace_free(q, bt);
-	return ret;
 }
 
 int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
···
 		    char __user *arg)
 {
 	struct blk_user_trace_setup buts;
+	struct blk_trace *bt;
 	int ret;
 
 	ret = copy_from_user(&buts, arg, sizeof(buts));
 	if (ret)
 		return -EFAULT;
 
+	if (!buts.buf_size || !buts.buf_nr)
+		return -EINVAL;
+
 	mutex_lock(&q->debugfs_mutex);
-	ret = do_blk_trace_setup(q, name, dev, bdev, &buts);
+	bt = blk_trace_setup_prepare(q, name, dev, buts.buf_size, buts.buf_nr,
+				     bdev);
+	if (IS_ERR(bt)) {
+		mutex_unlock(&q->debugfs_mutex);
+		return PTR_ERR(bt);
+	}
+	blk_trace_setup_finalize(q, name, bt, &buts);
 	mutex_unlock(&q->debugfs_mutex);
-	if (ret)
-		return ret;
 
 	if (copy_to_user(arg, &buts, sizeof(buts))) {
 		blk_trace_remove(q);
···
 {
 	struct blk_user_trace_setup buts;
 	struct compat_blk_user_trace_setup cbuts;
-	int ret;
+	struct blk_trace *bt;
 
 	if (copy_from_user(&cbuts, arg, sizeof(cbuts)))
 		return -EFAULT;
+
+	if (!cbuts.buf_size || !cbuts.buf_nr)
+		return -EINVAL;
 
 	buts = (struct blk_user_trace_setup) {
 		.act_mask = cbuts.act_mask,
···
 	};
 
 	mutex_lock(&q->debugfs_mutex);
-	ret = do_blk_trace_setup(q, name, dev, bdev, &buts);
+	bt = blk_trace_setup_prepare(q, name, dev, buts.buf_size, buts.buf_nr,
+				     bdev);
+	if (IS_ERR(bt)) {
+		mutex_unlock(&q->debugfs_mutex);
+		return PTR_ERR(bt);
+	}
+	blk_trace_setup_finalize(q, name, bt, &buts);
 	mutex_unlock(&q->debugfs_mutex);
-	if (ret)
-		return ret;
 
 	if (copy_to_user(arg, &buts.name, ARRAY_SIZE(buts.name))) {
 		blk_trace_remove(q);