[PATCH v4 1/2] dm-unstripe: unstripe RAID 0/dm-striped device

[Scott Bauer]

This device mapper module remaps and unstripes IO so it lands
solely on a single drive in a RAID 0/dm-stripe target.
In a 4 drive RAID 0 the mapper exposes 1/4th of the LBA range
as a virtual drive. Each IO to that virtual drive will land on
only one of the 4 drives, selected by the user.

Signed-off-by: Scott Bauer <scott.bauer@xxxxxxxxx>
Acked-by: Keith Busch <keith.busch@xxxxxxxxx>
---
 drivers/md/Kconfig       |  10 +++
 drivers/md/Makefile      |   1 +
 drivers/md/dm-unstripe.c | 204 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 215 insertions(+)
 create mode 100644 drivers/md/dm-unstripe.c

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 83b9362be09c..e1c48a7f98f1 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -269,6 +269,16 @@ config DM_BIO_PRISON
 
 source "drivers/md/persistent-data/Kconfig"
 
+config DM_UN_STRIPE
+       tristate "Transpose IO to individual drives on a raid device"
+       depends on BLK_DEV_DM
+       ---help---
+	  Enable this feature if you with to unstripe I/O on a RAID 0
+	  device to the respective drive. If your hardware has physical
+	  RAID 0 this module can unstripe the I/O to respective sides.
+
+	  If unsure say N.
+
 config DM_CRYPT
 	tristate "Crypt target support"
 	depends on BLK_DEV_DM
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index f701bb211783..2cc380b71319 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -43,6 +43,7 @@ obj-$(CONFIG_BCACHE)		+= bcache/
 obj-$(CONFIG_BLK_DEV_MD)	+= md-mod.o
 obj-$(CONFIG_BLK_DEV_DM)	+= dm-mod.o
 obj-$(CONFIG_BLK_DEV_DM_BUILTIN) += dm-builtin.o
+obj-$(CONFIG_DM_UN_STRIPE)   += dm-unstripe.o
 obj-$(CONFIG_DM_BUFIO)		+= dm-bufio.o
 obj-$(CONFIG_DM_BIO_PRISON)	+= dm-bio-prison.o
 obj-$(CONFIG_DM_CRYPT)		+= dm-crypt.o
diff --git a/drivers/md/dm-unstripe.c b/drivers/md/dm-unstripe.c
new file mode 100644
index 000000000000..086689fb11e3
--- /dev/null
+++ b/drivers/md/dm-unstripe.c
@@ -0,0 +1,204 @@
+/*
+ * Copyright  2017 Intel Corporation
+ *
+ * Authors:
+ *    Scott  Bauer      <scott.bauer@xxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#include "dm.h"
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/bitops.h>
+#include <linux/device-mapper.h>
+
+
+struct unstripe {
+	struct dm_dev *ddisk;
+	sector_t chunk_sectors;
+	sector_t stripe_sectors;
+	u8 chunk_shift;
+	u8 cur_drive;
+};
+
+
+#define DM_MSG_PREFIX "dm-unstripe"
+static const char *parse_err = "Please provide the necessary information:"
+	"<drive> <device (0 indexed)> <total_devices>"
+	" <chunk size in 512B sectors || 0 to use max hw sector size>";
+
+/*
+ * Argument layout:
+ * <drive> <stripe/drive to extract (0 indexed)>
+ *         <total_devices> <chunk size in 512B sect>
+ */
+static int set_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+	struct block_device *bbdev;
+	struct unstripe *target;
+	unsigned int chunk_size;
+	u64 tot_sec, mod;
+	u8 cur_drive, tot_drives;
+	char dummy;
+	int ret;
+
+	if (argc != 4) {
+		DMERR("%s", parse_err);
+		return -EINVAL;
+	}
+
+	if (sscanf(argv[1], "%hhu%c", &cur_drive, &dummy) != 1 ||
+	    sscanf(argv[2], "%hhu%c", &tot_drives, &dummy) != 1 ||
+	    sscanf(argv[3], "%u%c", &chunk_size, &dummy) != 1) {
+		DMERR("%s", parse_err);
+		return -EINVAL;
+	}
+
+	if (tot_drives == 0 || (cur_drive >= tot_drives && tot_drives > 1)) {
+		DMERR("Please provide a drive between [0,%hhu)", tot_drives);
+		return -EINVAL;
+	}
+
+	target = kzalloc(sizeof(*target), GFP_KERNEL);
+
+	if (!target) {
+		DMERR("Failed to allocate space for DM unstripe!");
+		return -ENOMEM;
+	}
+
+	ret = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
+			    &target->ddisk);
+	if (ret) {
+		kfree(target);
+		DMERR("dm-unstripe dev lookup failure! for drive %s", argv[0]);
+		return ret;
+	}
+
+	bbdev = target->ddisk->bdev;
+
+	target->cur_drive = cur_drive;
+	if (chunk_size)
+		target->chunk_sectors = chunk_size;
+	else
+		target->chunk_sectors =
+			queue_max_hw_sectors(bdev_get_queue(bbdev));
+
+	target->stripe_sectors = (tot_drives - 1) * target->chunk_sectors;
+	target->chunk_shift = fls(target->chunk_sectors) - 1;
+
+	ret = dm_set_target_max_io_len(ti, target->chunk_sectors);
+	if (ret) {
+		dm_put_device(ti, target->ddisk);
+		kfree(target);
+		DMERR("Failed to set max io len!");
+		return ret;
+	}
+	ti->private = target;
+
+	tot_sec = i_size_read(bbdev->bd_inode) >> SECTOR_SHIFT;
+	mod = tot_sec % target->chunk_sectors;
+
+	if (ti->len == 1)
+		ti->len = (tot_sec / tot_drives) - mod;
+	ti->begin = 0;
+	return 0;
+}
+
+static void set_dtr(struct dm_target *ti)
+{
+	struct unstripe *target = ti->private;
+
+	dm_put_device(ti, target->ddisk);
+	kfree(target);
+}
+
+
+static sector_t map_to_core(struct dm_target *ti, struct bio *bio)
+{
+	struct unstripe *target = ti->private;
+	unsigned long long sec = bio->bi_iter.bi_sector;
+	unsigned long long group;
+
+	group = (sec >> target->chunk_shift);
+	/* Account for what drive we're operating on */
+	sec += (target->cur_drive * target->chunk_sectors);
+	/* Shift us up to the right "row" on the drive*/
+	sec += target->stripe_sectors * group;
+	return sec;
+}
+
+static int set_map_bio(struct dm_target *ti, struct bio *bio)
+{
+	struct unstripe *target = ti->private;
+
+	if (bio_sectors(bio))
+		bio->bi_iter.bi_sector = map_to_core(ti, bio);
+
+	bio_set_dev(bio, target->ddisk->bdev);
+	submit_bio(bio);
+	return DM_MAPIO_SUBMITTED;
+}
+
+static void set_iohints(struct dm_target *ti,
+			struct queue_limits *limits)
+{
+	struct unstripe *target = ti->private;
+	struct queue_limits *lim = &bdev_get_queue(target->ddisk->bdev)->limits;
+
+	blk_limits_io_min(limits, lim->io_min);
+	blk_limits_io_opt(limits, lim->io_opt);
+	limits->chunk_sectors = target->chunk_sectors;
+}
+
+static int set_iterate(struct dm_target *ti, iterate_devices_callout_fn fn,
+		       void *data)
+{
+	struct unstripe *target = ti->private;
+
+	return fn(ti, target->ddisk, 0, ti->len, data);
+}
+
+static struct target_type iset_target = {
+	.name = "unstripe",
+	.version = {1, 0, 0},
+	.module = THIS_MODULE,
+	.ctr = set_ctr,
+	.dtr = set_dtr,
+	.map = set_map_bio,
+	.iterate_devices = set_iterate,
+	.io_hints = set_iohints,
+};
+
+static int __init dm_unstripe_init(void)
+{
+	int r = dm_register_target(&iset_target);
+
+	if (r < 0)
+		DMERR("register failed %d", r);
+
+	return r;
+}
+
+static void __exit dm_unstripe_exit(void)
+{
+	dm_unregister_target(&iset_target);
+}
+
+module_init(dm_unstripe_init);
+module_exit(dm_unstripe_exit);
+
+MODULE_DESCRIPTION(DM_NAME " DM unstripe");
+MODULE_ALIAS("dm-unstripe");
+MODULE_AUTHOR("Scott Bauer <scott.bauer@xxxxxxxxx>");
+MODULE_LICENSE("GPL");
-- 
2.11.0