1 files changed, 81 insertions, 0 deletions

diff --git a/drivers/md/dm-zero.c b/drivers/md/dm-zero.c
new file mode 100644
index 000000000000..7febc2cac73d
--- /dev/null
+++ b/drivers/md/dm-zero.c
@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2003 Christophe Saout <christophe@saout.de>
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm.h"
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/bio.h>
+
+/*
+ * Construct a dummy mapping that only returns zeros
+ */
+static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+        if (argc != 0) {
+                ti->error = "dm-zero: No arguments required";
+                return -EINVAL;
+        }
+
+        return 0;
+}
+
+/*
+ * Return zeros only on reads
+ */
+static int zero_map(struct dm_target *ti, struct bio *bio,
+                      union map_info *map_context)
+{
+        switch(bio_rw(bio)) {
+        case READ:
+                zero_fill_bio(bio);
+                break;
+        case READA:
+                /* readahead of null bytes only wastes buffer cache */
+                return -EIO;
+        case WRITE:
+                /* writes get silently dropped */
+                break;
+        }
+
+        bio_endio(bio, bio->bi_size, 0);
+
+        /* accepted bio, don't make new request */
+        return 0;
+}
+
+static struct target_type zero_target = {
+        .name   = "zero",
+        .version = {1, 0, 0},
+        .module = THIS_MODULE,
+        .ctr    = zero_ctr,
+        .map    = zero_map,
+};
+
+int __init dm_zero_init(void)
+{
+        int r = dm_register_target(&zero_target);
+
+        if (r < 0)
+                DMERR("zero: register failed %d", r);
+
+        return r;
+}
+
+void __exit dm_zero_exit(void)
+{
+        int r = dm_unregister_target(&zero_target);
+
+        if (r < 0)
+                DMERR("zero: unregister failed %d", r);
+}
+
+module_init(dm_zero_init)
+module_exit(dm_zero_exit)
+
+MODULE_AUTHOR("Christophe Saout <christophe@saout.de>");
+MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
+MODULE_LICENSE("GPL");