dm-switch.c

/*
 * Copyright (C) 2010-2012 by Dell Inc.  All rights reserved.
 * Copyright (C) 2011-2013 Red Hat, Inc.
 *
 * This file is released under the GPL.
 *
 * dm-switch is a device-mapper target that maps IO to underlying block
 * devices efficiently when there are a large number of fixed-sized
 * address regions but there is no simple pattern to allow for a compact
 * mapping representation such as dm-stripe.
 */

#include <linux/device-mapper.h>

#include <linux/module.h>
#include <linux/init.h>
#include <linux/vmalloc.h>

#define DM_MSG_PREFIX "switch"

/*
 * One region_table_slot_t holds <region_entries_per_slot> region table
 * entries each of which is <region_table_entry_bits> in size.
 */
typedef unsigned long region_table_slot_t;

/*
 * A device with the offset to its start sector.
 */
struct switch_path {
	struct dm_dev *dmdev;
	sector_t start;
};

/*
 * Context block for a dm switch device.
 */
struct switch_ctx {
	struct dm_target *ti;

	unsigned nr_paths;		/* Number of paths in path_list. */

	unsigned region_size;		/* Region size in 512-byte sectors */
	unsigned long nr_regions;	/* Number of regions making up the device */
	signed char region_size_bits;	/* log2 of region_size or -1 */

	unsigned char region_table_entry_bits;	/* Number of bits in one region table entry */
	unsigned char region_entries_per_slot;	/* Number of entries in one region table slot */
	signed char region_entries_per_slot_bits;	/* log2 of region_entries_per_slot or -1 */

	region_table_slot_t *region_table;	/* Region table */

	/*
	 * Array of dm devices to switch between.
	 */
	struct switch_path path_list[];
};

static struct switch_ctx *alloc_switch_ctx(struct dm_target *ti, unsigned nr_paths,
					   unsigned region_size)
{
	struct switch_ctx *sctx;

	sctx = kzalloc(struct_size(sctx, path_list, nr_paths), GFP_KERNEL);
	if (!sctx)
		return NULL;

	sctx->ti = ti;
	sctx->region_size = region_size;

	ti->private = sctx;

	return sctx;
}

static int alloc_region_table(struct dm_target *ti, unsigned nr_paths)
{
	struct switch_ctx *sctx = ti->private;
	sector_t nr_regions = ti->len;
	sector_t nr_slots;

	if (!(sctx->region_size & (sctx->region_size - 1)))
		sctx->region_size_bits = __ffs(sctx->region_size);
	else
		sctx->region_size_bits = -1;

	sctx->region_table_entry_bits = 1;
	while (sctx->region_table_entry_bits < sizeof(region_table_slot_t) * 8 &&
	       (region_table_slot_t)1 << sctx->region_table_entry_bits < nr_paths)
		sctx->region_table_entry_bits++;

	sctx->region_entries_per_slot = (sizeof(region_table_slot_t) * 8) / sctx->region_table_entry_bits;
	if (!(sctx->region_entries_per_slot & (sctx->region_entries_per_slot - 1)))
		sctx->region_entries_per_slot_bits = __ffs(sctx->region_entries_per_slot);
	else
		sctx->region_entries_per_slot_bits = -1;

	if (sector_div(nr_regions, sctx->region_size))
		nr_regions++;

	if (nr_regions >= ULONG_MAX) {
		ti->error = "Region table too large";
		return -EINVAL;
	}
	sctx->nr_regions = nr_regions;

	nr_slots = nr_regions;
	if (sector_div(nr_slots, sctx->region_entries_per_slot))
		nr_slots++;

	if (nr_slots > ULONG_MAX / sizeof(region_table_slot_t)) {
		ti->error = "Region table too large";
		return -EINVAL;
	}

	sctx->region_table = vmalloc(array_size(nr_slots,
						sizeof(region_table_slot_t)));
	if (!sctx->region_table) {
		ti->error = "Cannot allocate region table";
		return -ENOMEM;
	}

	return 0;
}

static void switch_get_position(struct switch_ctx *sctx, unsigned long region_nr,
				unsigned long *region_index, unsigned *bit)
{
	if (sctx->region_entries_per_slot_bits >= 0) {
		*region_index = region_nr >> sctx->region_entries_per_slot_bits;
		*bit = region_nr & (sctx->region_entries_per_slot - 1);
	} else {
		*region_index = region_nr / sctx->region_entries_per_slot;
		*bit = region_nr % sctx->region_entries_per_slot;
	}

	*bit *= sctx->region_table_entry_bits;
}

static unsigned switch_region_table_read(struct switch_ctx *sctx, unsigned long region_nr)
{
	unsigned long region_index;
	unsigned bit;

	switch_get_position(sctx, region_nr, &region_index, &bit);

	return (READ_ONCE(sctx->region_table[region_index]) >> bit) &
		((1 << sctx->region_table_entry_bits) - 1);
}

/*
 * Find which path to use at given offset.
 */
static unsigned switch_get_path_nr(struct switch_ctx *sctx, sector_t offset)
{
	unsigned path_nr;
	sector_t p;

	p = offset;
	if (sctx->region_size_bits >= 0)
		p >>= sctx->region_size_bits;
	else
		sector_div(p, sctx->region_size);

	path_nr = switch_region_table_read(sctx, p);

	/* This can only happen if the processor uses non-atomic stores. */
	if (unlikely(path_nr >= sctx->nr_paths))
		path_nr = 0;

	return path_nr;
}

static void switch_region_table_write(struct switch_ctx *sctx, unsigned long region_nr,
				      unsigned value)
{
	unsigned long region_index;
	unsigned bit;
	region_table_slot_t pte;

	switch_get_position(sctx, region_nr, &region_index, &bit);

	pte = sctx->region_table[region_index];
	pte &= ~((((region_table_slot_t)1 << sctx->region_table_entry_bits) - 1) << bit);
	pte |= (region_table_slot_t)value << bit;
	sctx->region_table[region_index] = pte;
}

/*
 * Fill the region table with an initial round robin pattern.
 */
static void initialise_region_table(struct switch_ctx *sctx)
{
	unsigned path_nr = 0;
	unsigned long region_nr;

	for (region_nr = 0; region_nr < sctx->nr_regions; region_nr++) {
		switch_region_table_write(sctx, region_nr, path_nr);
		if (++path_nr >= sctx->nr_paths)
			path_nr = 0;
	}
}

static int parse_path(struct dm_arg_set *as, struct dm_target *ti)
{
	struct switch_ctx *sctx = ti->private;
	unsigned long long start;
	int r;

	r = dm_get_device(ti, dm_shift_arg(as), dm_table_get_mode(ti->table),
			  &sctx->path_list[sctx->nr_paths].dmdev);
	if (r) {
		ti->error = "Device lookup failed";
		return r;
	}

	if (kstrtoull(dm_shift_arg(as), 10, &start) || start != (sector_t)start) {
		ti->error = "Invalid device starting offset";
		dm_put_device(ti, sctx->path_list[sctx->nr_paths].dmdev);
		return -EINVAL;
	}

	sctx->path_list[sctx->nr_paths].start = start;

	sctx->nr_paths++;

	return 0;
}

/*
 * Destructor: Don't free the dm_target, just the ti->private data (if any).
 */
static void switch_dtr(struct dm_target *ti)
{
	struct switch_ctx *sctx = ti->private;

	while (sctx->nr_paths--)
		dm_put_device(ti, sctx->path_list[sctx->nr_paths].dmdev);

	vfree(sctx->region_table);
	kfree(sctx);
}

/*
 * Constructor arguments:
 *   <num_paths> <region_size> <num_optional_args> [<optional_args>...]
 *   [<dev_path> <offset>]+
 *
 * Optional args are to allow for future extension: currently this
 * parameter must be 0.
 */
static int switch_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
	static const struct dm_arg _args[] = {
		{1, (KMALLOC_MAX_SIZE - sizeof(struct switch_ctx)) / sizeof(struct switch_path), "Invalid number of paths"},
		{1, UINT_MAX, "Invalid region size"},
		{0, 0, "Invalid number of optional args"},
	};

	struct switch_ctx *sctx;
	struct dm_arg_set as;
	unsigned nr_paths, region_size, nr_optional_args;
	int r;

	as.argc = argc;
	as.argv = argv;

	r = dm_read_arg(_args, &as, &nr_paths, &ti->error);
	if (r)
		return -EINVAL;

	r = dm_read_arg(_args + 1, &as, &region_size, &ti->error);
	if (r)
		return r;

	r = dm_read_arg_group(_args + 2, &as, &nr_optional_args, &ti->error);
	if (r)
		return r;
	/* parse optional arguments here, if we add any */

	if (as.argc != nr_paths * 2) {
		ti->error = "Incorrect number of path arguments";
		return -EINVAL;
	}

	sctx = alloc_switch_ctx(ti, nr_paths, region_size);
	if (!sctx) {
		ti->error = "Cannot allocate redirection context";
		return -ENOMEM;
	}

	r = dm_set_target_max_io_len(ti, region_size);
	if (r)
		goto error;

	while (as.argc) {
		r = parse_path(&as, ti);
		if (r)
			goto error;
	}

	r = alloc_region_table(ti, nr_paths);
	if (r)
		goto error;

	initialise_region_table(sctx);

	/* For UNMAP, sending the request down any path is sufficient */
	ti->num_discard_bios = 1;

	return 0;

error:
	switch_dtr(ti);

	return r;
}

static int switch_map(struct dm_target *ti, struct bio *bio)
{
	struct switch_ctx *sctx = ti->private;
	sector_t offset = dm_target_offset(ti, bio->bi_iter.bi_sector);
	unsigned path_nr = switch_get_path_nr(sctx, offset);

	bio_set_dev(bio, sctx->path_list[path_nr].dmdev->bdev);
	bio->bi_iter.bi_sector = sctx->path_list[path_nr].start + offset;

	return DM_MAPIO_REMAPPED;
}

/*
 * We need to parse hex numbers in the message as quickly as possible.
 *
 * This table-based hex parser improves performance.
 * It improves a time to load 1000000 entries compared to the condition-based
 * parser.
 *		table-based parser	condition-based parser
 * PA-RISC	0.29s			0.31s
 * Opteron	0.0495s			0.0498s
 */
static const unsigned char hex_table[256] = {
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 255, 255, 255, 255, 255, 255,
255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255
};

static __always_inline unsigned long parse_hex(const char **string)
{
	unsigned char d;
	unsigned long r = 0;

	while ((d = hex_table[(unsigned char)**string]) < 16) {
		r = (r << 4) | d;
		(*string)++;
	}

	return r;
}

static int process_set_region_mappings(struct switch_ctx *sctx,
				       unsigned argc, char **argv)
{
	unsigned i;
	unsigned long region_index = 0;

	for (i = 1; i < argc; i++) {
		unsigned long path_nr;
		const char *string = argv[i];

		if ((*string & 0xdf) == 'R') {
			unsigned long cycle_length, num_write;

			string++;
			if (unlikely(*string == ',')) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}
			cycle_length = parse_hex(&string);
			if (unlikely(*string != ',')) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}
			string++;
			if (unlikely(!*string)) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}
			num_write = parse_hex(&string);
			if (unlikely(*string)) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}

			if (unlikely(!cycle_length) || unlikely(cycle_length - 1 > region_index)) {
				DMWARN("invalid set_region_mappings cycle length: %lu > %lu",
				       cycle_length - 1, region_index);
				return -EINVAL;
			}
			if (unlikely(region_index + num_write < region_index) ||
			    unlikely(region_index + num_write >= sctx->nr_regions)) {
				DMWARN("invalid set_region_mappings region number: %lu + %lu >= %lu",
				       region_index, num_write, sctx->nr_regions);
				return -EINVAL;
			}

			while (num_write--) {
				region_index++;
				path_nr = switch_region_table_read(sctx, region_index - cycle_length);
				switch_region_table_write(sctx, region_index, path_nr);
			}

			continue;
		}

		if (*string == ':')
			region_index++;
		else {
			region_index = parse_hex(&string);
			if (unlikely(*string != ':')) {
				DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
				return -EINVAL;
			}
		}

		string++;
		if (unlikely(!*string)) {
			DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
			return -EINVAL;
		}

		path_nr = parse_hex(&string);
		if (unlikely(*string)) {
			DMWARN("invalid set_region_mappings argument: '%s'", argv[i]);
			return -EINVAL;
		}
		if (unlikely(region_index >= sctx->nr_regions)) {
			DMWARN("invalid set_region_mappings region number: %lu >= %lu", region_index, sctx->nr_regions);
			return -EINVAL;
		}
		if (unlikely(path_nr >= sctx->nr_paths)) {
			DMWARN("invalid set_region_mappings device: %lu >= %u", path_nr, sctx->nr_paths);
			return -EINVAL;
		}

		switch_region_table_write(sctx, region_index, path_nr);
	}

	return 0;
}

/*
 * Messages are processed one-at-a-time.
 *
 * Only set_region_mappings is supported.
 */
static int switch_message(struct dm_target *ti, unsigned argc, char **argv,
			  char *result, unsigned maxlen)
{
	static DEFINE_MUTEX(message_mutex);

	struct switch_ctx *sctx = ti->private;
	int r = -EINVAL;

	mutex_lock(&message_mutex);

	if (!strcasecmp(argv[0], "set_region_mappings"))
		r = process_set_region_mappings(sctx, argc, argv);
	else
		DMWARN("Unrecognised message received.");

	mutex_unlock(&message_mutex);

	return r;
}

static void switch_status(struct dm_target *ti, status_type_t type,
			  unsigned status_flags, char *result, unsigned maxlen)
{
	struct switch_ctx *sctx = ti->private;
	unsigned sz = 0;
	int path_nr;

	switch (type) {
	case STATUSTYPE_INFO:
		result[0] = '\0';
		break;

	case STATUSTYPE_TABLE:
		DMEMIT("%u %u 0", sctx->nr_paths, sctx->region_size);
		for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++)
			DMEMIT(" %s %llu", sctx->path_list[path_nr].dmdev->name,
			       (unsigned long long)sctx->path_list[path_nr].start);
		break;
	}
}

/*
 * Switch ioctl:
 *
 * Passthrough all ioctls to the path for sector 0
 */
static int switch_prepare_ioctl(struct dm_target *ti, struct block_device **bdev)
{
	struct switch_ctx *sctx = ti->private;
	unsigned path_nr;

	path_nr = switch_get_path_nr(sctx, 0);

	*bdev = sctx->path_list[path_nr].dmdev->bdev;

	/*
	 * Only pass ioctls through if the device sizes match exactly.
	 */
	if (ti->len + sctx->path_list[path_nr].start !=
	    i_size_read((*bdev)->bd_inode) >> SECTOR_SHIFT)
		return 1;
	return 0;
}

static int switch_iterate_devices(struct dm_target *ti,
				  iterate_devices_callout_fn fn, void *data)
{
	struct switch_ctx *sctx = ti->private;
	int path_nr;
	int r;

	for (path_nr = 0; path_nr < sctx->nr_paths; path_nr++) {
		r = fn(ti, sctx->path_list[path_nr].dmdev,
			 sctx->path_list[path_nr].start, ti->len, data);
		if (r)
			return r;
	}

	return 0;
}

static struct target_type switch_target = {
	.name = "switch",
	.version = {1, 1, 0},
	.module = THIS_MODULE,
	.ctr = switch_ctr,
	.dtr = switch_dtr,
	.map = switch_map,
	.message = switch_message,
	.status = switch_status,
	.prepare_ioctl = switch_prepare_ioctl,
	.iterate_devices = switch_iterate_devices,
};

static int __init dm_switch_init(void)
{
	int r;

	r = dm_register_target(&switch_target);
	if (r < 0)
		DMERR("dm_register_target() failed %d", r);

	return r;
}

static void __exit dm_switch_exit(void)
{
	dm_unregister_target(&switch_target);
}

module_init(dm_switch_init);
module_exit(dm_switch_exit);

MODULE_DESCRIPTION(DM_NAME " dynamic path switching target");
MODULE_AUTHOR("Kevin D. O'Kelley <Kevin_OKelley@dell.com>");
MODULE_AUTHOR("Narendran Ganapathy <Narendran_Ganapathy@dell.com>");
MODULE_AUTHOR("Jim Ramsay <Jim_Ramsay@dell.com>");
MODULE_AUTHOR("Mikulas Patocka <mpatocka@redhat.com>");
MODULE_LICENSE("GPL");