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Date: Tue, 15 Oct 2002 18:47:28 +0100
To: Linux Mailing List <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@transmeta.com>, Dave Jones <davej@suse.de>
Subject: [PATCH] Device-mapper submission 5/7
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From: Joe Thornber <joe@fib011235813.fsnet.co.uk>
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[Device mapper]
The stripe target.  Maps a range of logical sectors across many
physical volumes.

--- a/drivers/md/Makefile	Tue Oct 15 18:24:37 2002
+++ b/drivers/md/Makefile	Tue Oct 15 18:24:37 2002
@@ -4,7 +4,8 @@
 
 export-objs	:= md.o xor.o dm-table.o dm-target.o
 lvm-mod-objs	:= lvm.o lvm-snap.o lvm-fs.o
-dm-mod-objs	:= dm.o dm-hash.o dm-table.o dm-target.o dm-linear.o
+dm-mod-objs	:= dm.o dm-hash.o dm-table.o dm-target.o dm-linear.o \
+		   dm-stripe.o
 
 # Note: link order is important.  All raid personalities
 # and xor.o must come before md.o, as they each initialise 
--- /dev/null	Wed Dec 31 16:00:00 1969
+++ b/drivers/md/dm-stripe.c	Tue Oct 15 18:24:37 2002
@@ -0,0 +1,258 @@
+/*
+ * Copyright (C) 2001 Sistina Software (UK) Limited.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm.h"
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+
+struct stripe {
+	struct dm_dev *dev;
+	sector_t physical_start;
+};
+
+struct stripe_c {
+	uint32_t stripes;
+
+	/* The size of this target / num. stripes */
+	uint32_t stripe_width;
+
+	/* stripe chunk size */
+	uint32_t chunk_shift;
+	sector_t chunk_mask;
+
+	struct stripe stripe[0];
+};
+
+static inline struct stripe_c *alloc_context(int stripes)
+{
+	size_t len;
+
+	if (array_too_big(sizeof(struct stripe_c), sizeof(struct stripe),
+			  stripes))
+		return NULL;
+
+	len = sizeof(struct stripe_c) + (sizeof(struct stripe) * stripes);
+
+	return kmalloc(len, GFP_KERNEL);
+}
+
+/*
+ * Parse a single <dev> <sector> pair
+ */
+static int get_stripe(struct dm_target *ti, struct stripe_c *sc,
+		      int stripe, char **argv)
+{
+	char *end;
+	unsigned long start;
+
+	start = simple_strtoul(argv[1], &end, 10);
+	if (*end)
+		return -EINVAL;
+
+	if (dm_get_device(ti, argv[0], start, sc->stripe_width,
+			  ti->table->mode, &sc->stripe[stripe].dev))
+		return -ENXIO;
+
+	sc->stripe[stripe].physical_start = start;
+	return 0;
+}
+
+/*
+ * FIXME: Nasty function, only present because we can't link
+ * against __moddi3 and __divdi3.
+ *
+ * returns a == b * n
+ */
+static int multiple(sector_t a, sector_t b, sector_t *n)
+{
+	sector_t acc, prev, i;
+
+	*n = 0;
+	while (a >= b) {
+		for (acc = b, prev = 0, i = 1;
+		     acc <= a;
+		     prev = acc, acc <<= 1, i <<= 1)
+			;
+
+		a -= prev;
+		*n += i >> 1;
+	}
+
+	return a == 0;
+}
+
+/*
+ * Construct a striped mapping.
+ * <number of stripes> <chunk size (2^^n)> [<dev_path> <offset>]+
+ */
+static int stripe_ctr(struct dm_target *ti, int argc, char **argv)
+{
+	struct stripe_c *sc;
+	sector_t width;
+	uint32_t stripes;
+	uint32_t chunk_size;
+	char *end;
+	int r, i;
+
+	if (argc < 2) {
+		ti->error = "dm-stripe: Not enough arguments";
+		return -EINVAL;
+	}
+
+	stripes = simple_strtoul(argv[0], &end, 10);
+	if (*end) {
+		ti->error = "dm-stripe: Invalid stripe count";
+		return -EINVAL;
+	}
+
+	chunk_size = simple_strtoul(argv[1], &end, 10);
+	if (*end) {
+		ti->error = "dm-stripe: Invalid chunk_size";
+		return -EINVAL;
+	}
+
+	if (!multiple(ti->len, stripes, &width)) {
+		ti->error = "dm-stripe: Target length not divisable by "
+		    "number of stripes";
+		return -EINVAL;
+	}
+
+	sc = alloc_context(stripes);
+	if (!sc) {
+		ti->error = "dm-stripe: Memory allocation for striped context "
+		    "failed";
+		return -ENOMEM;
+	}
+
+	sc->stripes = stripes;
+	sc->stripe_width = width;
+	ti->split_io = chunk_size;
+
+	/*
+	 * chunk_size is a power of two
+	 */
+	if (!chunk_size || (chunk_size & (chunk_size - 1))) {
+		ti->error = "dm-stripe: Invalid chunk size";
+		kfree(sc);
+		return -EINVAL;
+	}
+
+	sc->chunk_mask = ((sector_t) chunk_size) - 1;
+	for (sc->chunk_shift = 0; chunk_size; sc->chunk_shift++)
+		chunk_size >>= 1;
+	sc->chunk_shift--;
+
+	/*
+	 * Get the stripe destinations.
+	 */
+	for (i = 0; i < stripes; i++) {
+		if (argc < 2) {
+			ti->error = "dm-stripe: Not enough destinations "
+				"specified";
+			kfree(sc);
+			return -EINVAL;
+		}
+
+		argv += 2;
+
+		r = get_stripe(ti, sc, i, argv);
+		if (r < 0) {
+			ti->error = "dm-stripe: Couldn't parse stripe "
+				"destination";
+			while (i--)
+				dm_put_device(ti, sc->stripe[i].dev);
+			kfree(sc);
+			return r;
+		}
+	}
+
+	ti->private = sc;
+	return 0;
+}
+
+static void stripe_dtr(struct dm_target *ti)
+{
+	unsigned int i;
+	struct stripe_c *sc = (struct stripe_c *) ti->private;
+
+	for (i = 0; i < sc->stripes; i++)
+		dm_put_device(ti, sc->stripe[i].dev);
+
+	kfree(sc);
+}
+
+static int stripe_map(struct dm_target *ti, struct bio *bio)
+{
+	struct stripe_c *sc = (struct stripe_c *) ti->private;
+
+	sector_t offset = bio->bi_sector - ti->begin;
+	uint32_t chunk = (uint32_t) (offset >> sc->chunk_shift);
+	uint32_t stripe = chunk % sc->stripes;	/* 32bit modulus */
+	chunk = chunk / sc->stripes;
+
+	bio->bi_bdev = sc->stripe[stripe].dev->bdev;
+	bio->bi_sector = sc->stripe[stripe].physical_start +
+	    (chunk << sc->chunk_shift) + (offset & sc->chunk_mask);
+	return 1;
+}
+
+static int stripe_status(struct dm_target *ti,
+			 status_type_t type, char *result, int maxlen)
+{
+	struct stripe_c *sc = (struct stripe_c *) ti->private;
+	int offset;
+	int i;
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		result[0] = '\0';
+		break;
+
+	case STATUSTYPE_TABLE:
+		offset = snprintf(result, maxlen, "%d " SECTOR_FORMAT,
+				  sc->stripes, sc->chunk_mask + 1);
+		for (i = 0; i < sc->stripes; i++) {
+			offset +=
+			    snprintf(result + offset, maxlen - offset,
+				     " %s " SECTOR_FORMAT,
+				     kdevname(sc->stripe[i].dev->dev),
+				     sc->stripe[i].physical_start);
+		}
+		break;
+	}
+	return 0;
+}
+
+static struct target_type stripe_target = {
+	.name   = "striped",
+	.module = THIS_MODULE,
+	.ctr    = stripe_ctr,
+	.dtr    = stripe_dtr,
+	.map    = stripe_map,
+	.status = stripe_status,
+};
+
+int __init dm_stripe_init(void)
+{
+	int r;
+
+	r = dm_register_target(&stripe_target);
+	if (r < 0)
+		DMWARN("striped target registration failed");
+
+	return r;
+}
+
+void dm_stripe_exit(void)
+{
+	if (dm_unregister_target(&stripe_target))
+		DMWARN("striped target unregistration failed");
+
+	return;
+}
--- a/drivers/md/dm.c	Tue Oct 15 18:24:37 2002
+++ b/drivers/md/dm.c	Tue Oct 15 18:24:37 2002
@@ -114,6 +114,7 @@
 	xx(dm_hash)
 	xx(dm_target)
 	xx(dm_linear)
+	xx(dm_stripe)
 #undef xx
 };
 
-
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