Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263435AbUFBPuX (ORCPT ); Wed, 2 Jun 2004 11:50:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263324AbUFBPuX (ORCPT ); Wed, 2 Jun 2004 11:50:23 -0400 Received: from mx1.redhat.com ([66.187.233.31]:19098 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S263435AbUFBPqL (ORCPT ); Wed, 2 Jun 2004 11:46:11 -0400 Date: Wed, 2 Jun 2004 16:46:05 +0100 From: Alasdair G Kergon To: Andrew Morton Cc: LKML Subject: [PATCH] 5/5: Device-mapper: dm-zero Message-ID: <20040602154605.GR6302@agk.surrey.redhat.com> Mail-Followup-To: Andrew Morton , LKML Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3197 Lines: 132 dm-zero --- diff/drivers/md/Kconfig 2004-06-01 19:56:27.000000000 -0500 +++ source/drivers/md/Kconfig 2004-06-01 19:56:47.000000000 -0500 @@ -193,5 +193,12 @@ Allow volume managers to mirror logical volumes, also needed for live data migration tools such as 'pvmove'. +config DM_ZERO + tristate "Zero target (EXPERIMENTAL)" + depends on BLK_DEV_DM && EXPERIMENTAL + ---help--- + A target that discards writes, and returns all zeroes for + reads. Useful in some recovery situations. + endmenu --- diff/drivers/md/Makefile 2004-06-01 19:56:27.000000000 -0500 +++ source/drivers/md/Makefile 2004-06-01 19:56:47.000000000 -0500 @@ -28,6 +28,7 @@ obj-$(CONFIG_DM_CRYPT) += dm-crypt.o obj-$(CONFIG_DM_SNAPSHOT) += dm-snapshot.o obj-$(CONFIG_DM_MIRROR) += dm-mirror.o +obj-$(CONFIG_DM_ZERO) += dm-zero.o quiet_cmd_unroll = UNROLL $@ cmd_unroll = $(PERL) $(srctree)/$(src)/unroll.pl $(UNROLL) \ --- diff/drivers/md/dm-zero.c 1969-12-31 18:00:00.000000000 -0600 +++ source/drivers/md/dm-zero.c 2004-06-01 19:56:47.000000000 -0500 @@ -0,0 +1,96 @@ +/* + * Copyright (C) 2003 Christophe Saout + * + * This file is released under the GPL. + */ + +#include "dm.h" + +#include +#include +#include + +/* + * 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); + bvec_kunmap_irq(bv, &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", + .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 "); +MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros"); +MODULE_LICENSE("GPL"); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/