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-rw-r--r--drivers/md/dm-zero.c88
1 files changed, 88 insertions, 0 deletions
diff --git a/drivers/md/dm-zero.c b/drivers/md/dm-zero.c
new file mode 100644
index 000000000..faa1dbffc
--- /dev/null
+++ b/drivers/md/dm-zero.c
@@ -0,0 +1,88 @@
+/*
+ * Copyright (C) 2003 Jana Saout <jana@saout.de>
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/device-mapper.h>
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/bio.h>
+
+#define DM_MSG_PREFIX "zero"
+
+/*
+ * 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 = "No arguments required";
+ return -EINVAL;
+ }
+
+ /*
+ * Silently drop discards, avoiding -EOPNOTSUPP.
+ */
+ ti->num_discard_bios = 1;
+
+ return 0;
+}
+
+/*
+ * Return zeros only on reads
+ */
+static int zero_map(struct dm_target *ti, struct bio *bio)
+{
+ switch (bio_op(bio)) {
+ case REQ_OP_READ:
+ if (bio->bi_opf & REQ_RAHEAD) {
+ /* readahead of null bytes only wastes buffer cache */
+ return DM_MAPIO_KILL;
+ }
+ zero_fill_bio(bio);
+ break;
+ case REQ_OP_WRITE:
+ /* writes get silently dropped */
+ break;
+ default:
+ return DM_MAPIO_KILL;
+ }
+
+ bio_endio(bio);
+
+ /* accepted bio, don't make new request */
+ return DM_MAPIO_SUBMITTED;
+}
+
+static struct target_type zero_target = {
+ .name = "zero",
+ .version = {1, 1, 0},
+ .features = DM_TARGET_NOWAIT,
+ .module = THIS_MODULE,
+ .ctr = zero_ctr,
+ .map = zero_map,
+};
+
+static int __init dm_zero_init(void)
+{
+ int r = dm_register_target(&zero_target);
+
+ if (r < 0)
+ DMERR("register failed %d", r);
+
+ return r;
+}
+
+static void __exit dm_zero_exit(void)
+{
+ dm_unregister_target(&zero_target);
+}
+
+module_init(dm_zero_init)
+module_exit(dm_zero_exit)
+
+MODULE_AUTHOR("Jana Saout <jana@saout.de>");
+MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
+MODULE_LICENSE("GPL");