dm: new ioctl DM_DEV_REMAP_CMD

New ioctl DM_DEV_REMAP_CMD allow to remap bio requests
from regular block device to dm device.

Signed-off-by: Sergei Shtepa <sergei.shtepa@veeam.com>

drivers/md/dm-core.h

@@ -13,6 +13,7 @@
 #include <linux/ktime.h>
 #include <linux/genhd.h>
 #include <linux/blk-mq.h>
+#include <linux/rbtree.h>
 
 #include <trace/events/block.h>
 
@@ -109,6 +110,9 @@ struct mapped_device {
 	bool init_tio_pdu:1;
 
 	struct srcu_struct io_barrier;
+
+	/* interposer device for remap */
+	struct dm_interposed_dev *ip_dev;
 };
 
 void disable_discard(struct mapped_device *md);
@@ -164,6 +168,22 @@ struct dm_table {
 	struct dm_md_mempools *mempools;
 };
 
+struct dm_rb_range {
+	struct rb_node node;
+	sector_t start;		/* start sector of rb node */
+	sector_t last;		/* end sector of rb node */
+	sector_t _subtree_last; /* highest sector in subtree of rb node */
+};
+
+void dm_rb_insert(struct dm_rb_range *node, struct rb_root_cached *root);
+void dm_rb_remove(struct dm_rb_range *node, struct rb_root_cached *root);
+
+struct dm_rb_range *dm_rb_iter_first(struct rb_root_cached *root, sector_t start, sector_t last);
+struct dm_rb_range *dm_rb_iter_next(struct dm_rb_range *node, sector_t start, sector_t last);
+
+int dm_remap_install(struct mapped_device *md, const char *donor_device_name);
+int dm_remap_uninstall(struct mapped_device *md);
+
 static inline struct completion *dm_get_completion_from_kobject(struct kobject *kobj)
 {
 	return &container_of(kobj, struct dm_kobject_holder, kobj)->completion;

drivers/md/dm-ioctl.c

@@ -1649,6 +1649,40 @@ static int target_message(struct file *filp, struct dm_ioctl *param, size_t para
 	return r;
 }
 
+static inline int dev_remap_start(struct mapped_device *md, uint8_t *params)
+{
+	char *donor_device_name = (char *)params;
+
+	return dm_remap_install(md, donor_device_name);
+}
+static int dev_remap_finish(struct mapped_device *md)
+{
+	return dm_remap_uninstall(md);
+}
+
+static int dev_remap(struct file *filp, struct dm_ioctl *param, size_t param_size)
+{
+	int ret = 0;
+	struct mapped_device *md;
+	struct dm_remap_param *remap_param = (void *)(param) + param->data_start;
+
+	md = find_device(param);
+	if (!md)
+		return -ENXIO;
+
+	if (remap_param->cmd == REMAP_START_CMD)
+		ret = dev_remap_start(md, remap_param->params);
+	else if (remap_param->cmd == REMAP_FINISH_CMD)
+		ret = dev_remap_finish(md);
+	else {
+		DMWARN("Invalid remap command, %d", remap_param->cmd);
+		ret = -EINVAL;
+	}
+
+	dm_put(md);
+	return ret;
+}
+
 /*
  * The ioctl parameter block consists of two parts, a dm_ioctl struct
  * followed by a data buffer.  This flag is set if the second part,
@@ -1691,6 +1725,7 @@ static ioctl_fn lookup_ioctl(unsigned int cmd, int *ioctl_flags)
 		{DM_DEV_SET_GEOMETRY_CMD, 0, dev_set_geometry},
 		{DM_DEV_ARM_POLL, IOCTL_FLAGS_NO_PARAMS, dev_arm_poll},
 		{DM_GET_TARGET_VERSION, 0, get_target_version},
+		{DM_DEV_REMAP_CMD, 0, dev_remap},
 	};
 
 	if (unlikely(cmd >= ARRAY_SIZE(_ioctls)))