v4.19.13 snapshot.
diff --git a/drivers/md/dm-target.c b/drivers/md/dm-target.c
new file mode 100644
index 0000000..314d17c
--- /dev/null
+++ b/drivers/md/dm-target.c
@@ -0,0 +1,172 @@
+/*
+ * Copyright (C) 2001 Sistina Software (UK) Limited
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-core.h"
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kmod.h>
+#include <linux/bio.h>
+
+#define DM_MSG_PREFIX "target"
+
+static LIST_HEAD(_targets);
+static DECLARE_RWSEM(_lock);
+
+static inline struct target_type *__find_target_type(const char *name)
+{
+ struct target_type *tt;
+
+ list_for_each_entry(tt, &_targets, list)
+ if (!strcmp(name, tt->name))
+ return tt;
+
+ return NULL;
+}
+
+static struct target_type *get_target_type(const char *name)
+{
+ struct target_type *tt;
+
+ down_read(&_lock);
+
+ tt = __find_target_type(name);
+ if (tt && !try_module_get(tt->module))
+ tt = NULL;
+
+ up_read(&_lock);
+ return tt;
+}
+
+static void load_module(const char *name)
+{
+ request_module("dm-%s", name);
+}
+
+struct target_type *dm_get_target_type(const char *name)
+{
+ struct target_type *tt = get_target_type(name);
+
+ if (!tt) {
+ load_module(name);
+ tt = get_target_type(name);
+ }
+
+ return tt;
+}
+
+void dm_put_target_type(struct target_type *tt)
+{
+ down_read(&_lock);
+ module_put(tt->module);
+ up_read(&_lock);
+}
+
+int dm_target_iterate(void (*iter_func)(struct target_type *tt,
+ void *param), void *param)
+{
+ struct target_type *tt;
+
+ down_read(&_lock);
+ list_for_each_entry(tt, &_targets, list)
+ iter_func(tt, param);
+ up_read(&_lock);
+
+ return 0;
+}
+
+int dm_register_target(struct target_type *tt)
+{
+ int rv = 0;
+
+ down_write(&_lock);
+ if (__find_target_type(tt->name))
+ rv = -EEXIST;
+ else
+ list_add(&tt->list, &_targets);
+
+ up_write(&_lock);
+ return rv;
+}
+
+void dm_unregister_target(struct target_type *tt)
+{
+ down_write(&_lock);
+ if (!__find_target_type(tt->name)) {
+ DMCRIT("Unregistering unrecognised target: %s", tt->name);
+ BUG();
+ }
+
+ list_del(&tt->list);
+
+ up_write(&_lock);
+}
+
+/*
+ * io-err: always fails an io, useful for bringing
+ * up LVs that have holes in them.
+ */
+static int io_err_ctr(struct dm_target *tt, unsigned int argc, char **args)
+{
+ /*
+ * Return error for discards instead of -EOPNOTSUPP
+ */
+ tt->num_discard_bios = 1;
+
+ return 0;
+}
+
+static void io_err_dtr(struct dm_target *tt)
+{
+ /* empty */
+}
+
+static int io_err_map(struct dm_target *tt, struct bio *bio)
+{
+ return DM_MAPIO_KILL;
+}
+
+static int io_err_clone_and_map_rq(struct dm_target *ti, struct request *rq,
+ union map_info *map_context,
+ struct request **clone)
+{
+ return DM_MAPIO_KILL;
+}
+
+static void io_err_release_clone_rq(struct request *clone)
+{
+}
+
+static long io_err_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
+ long nr_pages, void **kaddr, pfn_t *pfn)
+{
+ return -EIO;
+}
+
+static struct target_type error_target = {
+ .name = "error",
+ .version = {1, 5, 0},
+ .features = DM_TARGET_WILDCARD,
+ .ctr = io_err_ctr,
+ .dtr = io_err_dtr,
+ .map = io_err_map,
+ .clone_and_map_rq = io_err_clone_and_map_rq,
+ .release_clone_rq = io_err_release_clone_rq,
+ .direct_access = io_err_dax_direct_access,
+};
+
+int __init dm_target_init(void)
+{
+ return dm_register_target(&error_target);
+}
+
+void dm_target_exit(void)
+{
+ dm_unregister_target(&error_target);
+}
+
+EXPORT_SYMBOL(dm_register_target);
+EXPORT_SYMBOL(dm_unregister_target);