[PATCH v9 09/29] libmultipath: Add support for block device IOCTL

[John Garry <john.garry@linux.dev>]

Add mpath_bdev_ioctl() as a multipath block device IOCTL handler. This
handler calls into the mpath_device bdev fops handler.

The .compat_ioctl handler is given the standard handler.

Signed-off-by: John Garry <john.garry@linux.dev>
---
 lib/multipath.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/lib/multipath.c b/lib/multipath.c
index ae5a73d570b3..d59d7ba81087 100644
--- a/lib/multipath.c
+++ b/lib/multipath.c
@@ -455,11 +455,53 @@ static void mpath_bdev_release(struct gendisk *disk)
 	mpath_put_head(mpath_head);
 }
 
+static int mpath_bdev_ioctl(struct block_device *bdev, blk_mode_t mode,
+		    unsigned int cmd, unsigned long arg)
+{
+	struct gendisk *disk = bdev->bd_disk;
+	struct mpath_head *mpath_head = mpath_gendisk_to_head(disk);
+	struct mpath_device *mpath_device;
+	int srcu_idx, err;
+
+	/*
+	 * This check is duplicated from sd_ioctl() as we don't pass the
+	 * partition bdev to fops->ioctl. That is not yet possible as the
+	 * per-path disk is hidden and, as such, does not have partitions
+	 * scanned.
+	 */
+	if (bdev_is_partition(bdev) && !capable(CAP_SYS_RAWIO))
+		return -ENOIOCTLCMD;
+
+	srcu_idx = srcu_read_lock(&mpath_head->srcu);
+	mpath_device = mpath_find_path(mpath_head);
+	if (!mpath_device) {
+		err = -EWOULDBLOCK;
+		goto out_unlock;
+	}
+
+	if (!mpath_device->disk->fops->ioctl) {
+		err = -ENOTTY;
+		goto out_unlock;
+	}
+
+	err = mpath_device->disk->fops->ioctl(
+			mpath_device->disk->part0, mode, cmd, arg);
+out_unlock:
+	srcu_read_unlock(&mpath_head->srcu, srcu_idx);
+	return err;
+}
+
 const struct block_device_operations mpath_ops = {
 	.owner          = THIS_MODULE,
 	.open		= mpath_bdev_open,
 	.release	= mpath_bdev_release,
 	.submit_bio	= mpath_bdev_submit_bio,
+	.ioctl		= mpath_bdev_ioctl,
+	/*
+	 * Both NVMe and SCSI use generic blkdev_compat_ptr_ioctl, so would
+	 * avoid their custom compat_ioctl implementation.
+	 */
+	.compat_ioctl	= blkdev_compat_ptr_ioctl,
 };
 EXPORT_SYMBOL_GPL(mpath_ops);
 
-- 
2.43.0