This commit was manufactured by cvs2svn to create branch 'vserver'.

[linux-2.6.git] / drivers / md / dm-zero.c

diff --git a/drivers/md/dm-zero.c b/drivers/md/dm-zero.c
new file mode 100644 (file)
index 0000000..725f2c8
--- /dev/null
+++ b/drivers/md/dm-zero.c
@@ -0,0 +1,98 @@
+/*
+ * 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;
+}
+
+/*
+ * Fills the bio pages with zeros
+ */
+static void zero_fill_bio(struct bio *bio)
+{
+       unsigned long flags;
+       struct bio_vec *bv;
+       int i;
+
+       bio_for_each_segment(bv, bio, i) {
+               char *data = bvec_kmap_irq(bv, &flags);
+               memset(data, 0, bv->bv_len);
+               flush_dcache_page(bv->bv_page);
+               bvec_kunmap_irq(data, &flags);
+       }
+}
+
+/*
+ * 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");