drivers/md/dm-io.c - kernel/msm-4.19 - Gitiles

 /*
  * Copyright (C) 2003 Sistina Software
  * Copyright (C) 2006 Red Hat GmbH
  *
  * This file is released under the GPL.
  */

 #include "dm.h"

 #include <linux/device-mapper.h>

 #include <linux/bio.h>
 #include <linux/mempool.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/dm-io.h>

 #define DM_MSG_PREFIX "io"

 #define DM_IO_MAX_REGIONS	BITS_PER_LONG

 struct dm_io_client {
 	mempool_t *pool;
 	struct bio_set *bios;
 };

 /*
  * Aligning 'struct io' reduces the number of bits required to store
  * its address.  Refer to store_io_and_region_in_bio() below.
  */
 struct io {
 	unsigned long error_bits;
 	unsigned long eopnotsupp_bits;
 	atomic_t count;
 	struct task_struct *sleeper;
 	struct dm_io_client *client;
 	io_notify_fn callback;
 	void *context;
 } __attribute__((aligned(DM_IO_MAX_REGIONS)));

 static struct kmem_cache *_dm_io_cache;

 /*
  * io contexts are only dynamically allocated for asynchronous
  * io.  Since async io is likely to be the majority of io we'll
  * have the same number of io contexts as bios! (FIXME: must reduce this).
  */

 static unsigned int pages_to_ios(unsigned int pages)
 {
 	return 4 * pages;	/* too many ? */
 }

 /*
  * Create a client with mempool and bioset.
  */
 struct dm_io_client *dm_io_client_create(unsigned num_pages)
 {
 	unsigned ios = pages_to_ios(num_pages);
 	struct dm_io_client *client;

 	client = kmalloc(sizeof(*client), GFP_KERNEL);
 	if (!client)
 		return ERR_PTR(-ENOMEM);

 	client->pool = mempool_create_slab_pool(ios, _dm_io_cache);
 	if (!client->pool)
 		goto bad;

 	client->bios = bioset_create(16, 0);
 	if (!client->bios)
 		goto bad;

 	return client;

    bad:
 	if (client->pool)
 		mempool_destroy(client->pool);
 	kfree(client);
 	return ERR_PTR(-ENOMEM);
 }
 EXPORT_SYMBOL(dm_io_client_create);

 int dm_io_client_resize(unsigned num_pages, struct dm_io_client *client)
 {
 	return mempool_resize(client->pool, pages_to_ios(num_pages),
 			      GFP_KERNEL);
 }
 EXPORT_SYMBOL(dm_io_client_resize);

 void dm_io_client_destroy(struct dm_io_client *client)
 {
 	mempool_destroy(client->pool);
 	bioset_free(client->bios);
 	kfree(client);
 }
 EXPORT_SYMBOL(dm_io_client_destroy);

 /*-----------------------------------------------------------------
  * We need to keep track of which region a bio is doing io for.
  * To avoid a memory allocation to store just 5 or 6 bits, we
  * ensure the 'struct io' pointer is aligned so enough low bits are
  * always zero and then combine it with the region number directly in
  * bi_private.
  *---------------------------------------------------------------*/
 static void store_io_and_region_in_bio(struct bio *bio, struct io *io,
 				       unsigned region)
 {
 	if (unlikely(!IS_ALIGNED((unsigned long)io, DM_IO_MAX_REGIONS))) {
 		DMCRIT("Unaligned struct io pointer %p", io);
 		BUG();
 	}

 	bio->bi_private = (void *)((unsigned long)io | region);
 }

 static void retrieve_io_and_region_from_bio(struct bio *bio, struct io **io,
 				       unsigned *region)
 {
 	unsigned long val = (unsigned long)bio->bi_private;

 	*io = (void *)(val & -(unsigned long)DM_IO_MAX_REGIONS);
 	*region = val & (DM_IO_MAX_REGIONS - 1);
 }

 /*-----------------------------------------------------------------
  * We need an io object to keep track of the number of bios that
  * have been dispatched for a particular io.
  *---------------------------------------------------------------*/
 static void dec_count(struct io *io, unsigned int region, int error)
 {
 	if (error) {
 		set_bit(region, &io->error_bits);
 		if (error == -EOPNOTSUPP)
 			set_bit(region, &io->eopnotsupp_bits);
 	}

 	if (atomic_dec_and_test(&io->count)) {
 		if (io->sleeper)
 			wake_up_process(io->sleeper);

 		else {
 			unsigned long r = io->error_bits;
 			io_notify_fn fn = io->callback;
 			void *context = io->context;

 			mempool_free(io, io->client->pool);
 			fn(r, context);
 		}
 	}
 }

 static void endio(struct bio *bio, int error)
 {
 	struct io *io;
 	unsigned region;

 	if (error && bio_data_dir(bio) == READ)
 		zero_fill_bio(bio);

 	/*
 	 * The bio destructor in bio_put() may use the io object.
 	 */
 	retrieve_io_and_region_from_bio(bio, &io, &region);

 	bio_put(bio);

 	dec_count(io, region, error);
 }

 /*-----------------------------------------------------------------
  * These little objects provide an abstraction for getting a new
  * destination page for io.
  *---------------------------------------------------------------*/
 struct dpages {
 	void (*get_page)(struct dpages *dp,
 			 struct page **p, unsigned long *len, unsigned *offset);
 	void (*next_page)(struct dpages *dp);

 	unsigned context_u;
 	void *context_ptr;
 };

 /*
  * Functions for getting the pages from a list.
  */
 static void list_get_page(struct dpages *dp,
 		  struct page **p, unsigned long *len, unsigned *offset)
 {
 	unsigned o = dp->context_u;
 	struct page_list *pl = (struct page_list *) dp->context_ptr;

 	*p = pl->page;
 	*len = PAGE_SIZE - o;
 	*offset = o;
 }

 static void list_next_page(struct dpages *dp)
 {
 	struct page_list *pl = (struct page_list *) dp->context_ptr;
 	dp->context_ptr = pl->next;
 	dp->context_u = 0;
 }

 static void list_dp_init(struct dpages *dp, struct page_list *pl, unsigned offset)
 {
 	dp->get_page = list_get_page;
 	dp->next_page = list_next_page;
 	dp->context_u = offset;
 	dp->context_ptr = pl;
 }

 /*
  * Functions for getting the pages from a bvec.
  */
 static void bvec_get_page(struct dpages *dp,
 		  struct page **p, unsigned long *len, unsigned *offset)
 {
 	struct bio_vec *bvec = (struct bio_vec *) dp->context_ptr;
 	*p = bvec->bv_page;
 	*len = bvec->bv_len;
 	*offset = bvec->bv_offset;
 }

 static void bvec_next_page(struct dpages *dp)
 {
 	struct bio_vec *bvec = (struct bio_vec *) dp->context_ptr;
 	dp->context_ptr = bvec + 1;
 }

 static void bvec_dp_init(struct dpages *dp, struct bio_vec *bvec)
 {
 	dp->get_page = bvec_get_page;
 	dp->next_page = bvec_next_page;
 	dp->context_ptr = bvec;
 }

 /*
  * Functions for getting the pages from a VMA.
  */
 static void vm_get_page(struct dpages *dp,
 		 struct page **p, unsigned long *len, unsigned *offset)
 {
 	*p = vmalloc_to_page(dp->context_ptr);
 	*offset = dp->context_u;
 	*len = PAGE_SIZE - dp->context_u;
 }

 static void vm_next_page(struct dpages *dp)
 {
 	dp->context_ptr += PAGE_SIZE - dp->context_u;
 	dp->context_u = 0;
 }

 static void vm_dp_init(struct dpages *dp, void *data)
 {
 	dp->get_page = vm_get_page;
 	dp->next_page = vm_next_page;
 	dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
 	dp->context_ptr = data;
 }

 static void dm_bio_destructor(struct bio *bio)
 {
 	unsigned region;
 	struct io *io;

 	retrieve_io_and_region_from_bio(bio, &io, &region);

 	bio_free(bio, io->client->bios);
 }

 /*
  * Functions for getting the pages from kernel memory.
  */
 static void km_get_page(struct dpages *dp, struct page **p, unsigned long *len,
 			unsigned *offset)
 {
 	*p = virt_to_page(dp->context_ptr);
 	*offset = dp->context_u;
 	*len = PAGE_SIZE - dp->context_u;
 }

 static void km_next_page(struct dpages *dp)
 {
 	dp->context_ptr += PAGE_SIZE - dp->context_u;
 	dp->context_u = 0;
 }

 static void km_dp_init(struct dpages *dp, void *data)
 {
 	dp->get_page = km_get_page;
 	dp->next_page = km_next_page;
 	dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
 	dp->context_ptr = data;
 }

 /*-----------------------------------------------------------------
  * IO routines that accept a list of pages.
  *---------------------------------------------------------------*/
 static void do_region(int rw, unsigned region, struct dm_io_region *where,
 		      struct dpages *dp, struct io *io)
 {
 	struct bio *bio;
 	struct page *page;
 	unsigned long len;
 	unsigned offset;
 	unsigned num_bvecs;
 	sector_t remaining = where->count;

 	while (remaining) {
 		/*
 		 * Allocate a suitably sized-bio.
 		 */
 		num_bvecs = dm_sector_div_up(remaining,
 					     (PAGE_SIZE >> SECTOR_SHIFT));
 		num_bvecs = min_t(int, bio_get_nr_vecs(where->bdev), num_bvecs);
 		bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, io->client->bios);
 		bio->bi_sector = where->sector + (where->count - remaining);
 		bio->bi_bdev = where->bdev;
 		bio->bi_end_io = endio;
 		bio->bi_destructor = dm_bio_destructor;
 		store_io_and_region_in_bio(bio, io, region);

 		/*
 		 * Try and add as many pages as possible.
 		 */
 		while (remaining) {
 			dp->get_page(dp, &page, &len, &offset);
 			len = min(len, to_bytes(remaining));
 			if (!bio_add_page(bio, page, len, offset))
 				break;

 			offset = 0;
 			remaining -= to_sector(len);
 			dp->next_page(dp);
 		}

 		atomic_inc(&io->count);
 		submit_bio(rw, bio);
 	}
 }

 static void dispatch_io(int rw, unsigned int num_regions,
 			struct dm_io_region *where, struct dpages *dp,
 			struct io *io, int sync)
 {
 	int i;
 	struct dpages old_pages = *dp;

 	BUG_ON(num_regions > DM_IO_MAX_REGIONS);

 	if (sync)
 		rw |= (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG);

 	/*
 	 * For multiple regions we need to be careful to rewind
 	 * the dp object for each call to do_region.
 	 */
 	for (i = 0; i < num_regions; i++) {
 		*dp = old_pages;
 		if (where[i].count)
 			do_region(rw, i, where + i, dp, io);
 	}

 	/*
 	 * Drop the extra reference that we were holding to avoid
 	 * the io being completed too early.
 	 */
 	dec_count(io, 0, 0);
 }

 static int sync_io(struct dm_io_client *client, unsigned int num_regions,
 		   struct dm_io_region *where, int rw, struct dpages *dp,
 		   unsigned long *error_bits)
 {
 	/*
 	 * gcc <= 4.3 can't do the alignment for stack variables, so we must
 	 * align it on our own.
 	 * volatile prevents the optimizer from removing or reusing
 	 * "io_" field from the stack frame (allowed in ANSI C).
 	 */
 	volatile char io_[sizeof(struct io) + __alignof__(struct io) - 1];
 	struct io *io = (struct io *)PTR_ALIGN(&io_, __alignof__(struct io));

 	if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
 		WARN_ON(1);
 		return -EIO;
 	}

 retry:
 	io->error_bits = 0;
 	io->eopnotsupp_bits = 0;
 	atomic_set(&io->count, 1); /* see dispatch_io() */
 	io->sleeper = current;
 	io->client = client;

 	dispatch_io(rw, num_regions, where, dp, io, 1);

 	while (1) {
 		set_current_state(TASK_UNINTERRUPTIBLE);

 		if (!atomic_read(&io->count))
 			break;

 		io_schedule();
 	}
 	set_current_state(TASK_RUNNING);

 	if (io->eopnotsupp_bits && (rw & (1 << BIO_RW_BARRIER))) {
 		rw &= ~(1 << BIO_RW_BARRIER);
 		goto retry;
 	}

 	if (error_bits)
 		*error_bits = io->error_bits;

 	return io->error_bits ? -EIO : 0;
 }

 static int async_io(struct dm_io_client *client, unsigned int num_regions,
 		    struct dm_io_region *where, int rw, struct dpages *dp,
 		    io_notify_fn fn, void *context)
 {
 	struct io *io;

 	if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
 		WARN_ON(1);
 		fn(1, context);
 		return -EIO;
 	}

 	io = mempool_alloc(client->pool, GFP_NOIO);
 	io->error_bits = 0;
 	io->eopnotsupp_bits = 0;
 	atomic_set(&io->count, 1); /* see dispatch_io() */
 	io->sleeper = NULL;
 	io->client = client;
 	io->callback = fn;
 	io->context = context;

 	dispatch_io(rw, num_regions, where, dp, io, 0);
 	return 0;
 }

 static int dp_init(struct dm_io_request *io_req, struct dpages *dp)
 {
 	/* Set up dpages based on memory type */
 	switch (io_req->mem.type) {
 	case DM_IO_PAGE_LIST:
 		list_dp_init(dp, io_req->mem.ptr.pl, io_req->mem.offset);
 		break;

 	case DM_IO_BVEC:
 		bvec_dp_init(dp, io_req->mem.ptr.bvec);
 		break;

 	case DM_IO_VMA:
 		vm_dp_init(dp, io_req->mem.ptr.vma);
 		break;

 	case DM_IO_KMEM:
 		km_dp_init(dp, io_req->mem.ptr.addr);
 		break;

 	default:
 		return -EINVAL;
 	}

 	return 0;
 }

 /*
  * New collapsed (a)synchronous interface.
  *
  * If the IO is asynchronous (i.e. it has notify.fn), you must either unplug
  * the queue with blk_unplug() some time later or set the BIO_RW_SYNC bit in
  * io_req->bi_rw. If you fail to do one of these, the IO will be submitted to
  * the disk after q->unplug_delay, which defaults to 3ms in blk-settings.c.
  */
 int dm_io(struct dm_io_request *io_req, unsigned num_regions,
 	  struct dm_io_region *where, unsigned long *sync_error_bits)
 {
 	int r;
 	struct dpages dp;

 	r = dp_init(io_req, &dp);
 	if (r)
 		return r;

 	if (!io_req->notify.fn)
 		return sync_io(io_req->client, num_regions, where,
 			       io_req->bi_rw, &dp, sync_error_bits);

 	return async_io(io_req->client, num_regions, where, io_req->bi_rw,
 			&dp, io_req->notify.fn, io_req->notify.context);
 }
 EXPORT_SYMBOL(dm_io);

 int __init dm_io_init(void)
 {
 	_dm_io_cache = KMEM_CACHE(io, 0);
 	if (!_dm_io_cache)
 		return -ENOMEM;

 	return 0;
 }

 void dm_io_exit(void)
 {
 	kmem_cache_destroy(_dm_io_cache);
 	_dm_io_cache = NULL;
 }
	/*
	* Copyright (C) 2003 Sistina Software
	* Copyright (C) 2006 Red Hat GmbH
	*
	* This file is released under the GPL.
	*/

	#include "dm.h"

	#include <linux/device-mapper.h>

	#include <linux/bio.h>
	#include <linux/mempool.h>
	#include <linux/module.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/dm-io.h>

	#define DM_MSG_PREFIX "io"

	#define DM_IO_MAX_REGIONS BITS_PER_LONG

	struct dm_io_client {
	mempool_t *pool;
	struct bio_set *bios;
	};

	/*
	* Aligning 'struct io' reduces the number of bits required to store
	* its address. Refer to store_io_and_region_in_bio() below.
	*/
	struct io {
	unsigned long error_bits;
	unsigned long eopnotsupp_bits;
	atomic_t count;
	struct task_struct *sleeper;
	struct dm_io_client *client;
	io_notify_fn callback;
	void *context;
	} __attribute__((aligned(DM_IO_MAX_REGIONS)));

	static struct kmem_cache *_dm_io_cache;

	/*
	* io contexts are only dynamically allocated for asynchronous
	* io. Since async io is likely to be the majority of io we'll
	* have the same number of io contexts as bios! (FIXME: must reduce this).
	*/

	static unsigned int pages_to_ios(unsigned int pages)
	{
	return 4 * pages; /* too many ? */
	}

	/*
	* Create a client with mempool and bioset.
	*/
	struct dm_io_client *dm_io_client_create(unsigned num_pages)
	{
	unsigned ios = pages_to_ios(num_pages);
	struct dm_io_client *client;

	client = kmalloc(sizeof(*client), GFP_KERNEL);
	if (!client)
	return ERR_PTR(-ENOMEM);

	client->pool = mempool_create_slab_pool(ios, _dm_io_cache);
	if (!client->pool)
	goto bad;

	client->bios = bioset_create(16, 0);
	if (!client->bios)
	goto bad;

	return client;

	bad:
	if (client->pool)
	mempool_destroy(client->pool);
	kfree(client);
	return ERR_PTR(-ENOMEM);
	}
	EXPORT_SYMBOL(dm_io_client_create);

	int dm_io_client_resize(unsigned num_pages, struct dm_io_client *client)
	{
	return mempool_resize(client->pool, pages_to_ios(num_pages),
	GFP_KERNEL);
	}
	EXPORT_SYMBOL(dm_io_client_resize);

	void dm_io_client_destroy(struct dm_io_client *client)
	{
	mempool_destroy(client->pool);
	bioset_free(client->bios);
	kfree(client);
	}
	EXPORT_SYMBOL(dm_io_client_destroy);

	/*-----------------------------------------------------------------
	* We need to keep track of which region a bio is doing io for.
	* To avoid a memory allocation to store just 5 or 6 bits, we
	* ensure the 'struct io' pointer is aligned so enough low bits are
	* always zero and then combine it with the region number directly in
	* bi_private.
	---------------------------------------------------------------/
	static void store_io_and_region_in_bio(struct bio bio, struct io io,
	unsigned region)
	{
	if (unlikely(!IS_ALIGNED((unsigned long)io, DM_IO_MAX_REGIONS))) {
	DMCRIT("Unaligned struct io pointer %p", io);
	BUG();
	}

	bio->bi_private = (void *)((unsigned long)io \| region);
	}

	static void retrieve_io_and_region_from_bio(struct bio bio, struct io *io,
	unsigned *region)
	{
	unsigned long val = (unsigned long)bio->bi_private;

	io = (void )(val & -(unsigned long)DM_IO_MAX_REGIONS);
	*region = val & (DM_IO_MAX_REGIONS - 1);
	}

	/*-----------------------------------------------------------------
	* We need an io object to keep track of the number of bios that
	* have been dispatched for a particular io.
	---------------------------------------------------------------/
	static void dec_count(struct io *io, unsigned int region, int error)
	{
	if (error) {
	set_bit(region, &io->error_bits);
	if (error == -EOPNOTSUPP)
	set_bit(region, &io->eopnotsupp_bits);
	}

	if (atomic_dec_and_test(&io->count)) {
	if (io->sleeper)
	wake_up_process(io->sleeper);

	else {
	unsigned long r = io->error_bits;
	io_notify_fn fn = io->callback;
	void *context = io->context;

	mempool_free(io, io->client->pool);
	fn(r, context);
	}
	}
	}

	static void endio(struct bio *bio, int error)
	{
	struct io *io;
	unsigned region;

	if (error && bio_data_dir(bio) == READ)
	zero_fill_bio(bio);

	/*
	* The bio destructor in bio_put() may use the io object.
	*/
	retrieve_io_and_region_from_bio(bio, &io, &region);

	bio_put(bio);

	dec_count(io, region, error);
	}

	/*-----------------------------------------------------------------
	* These little objects provide an abstraction for getting a new
	* destination page for io.
	---------------------------------------------------------------/
	struct dpages {
	void (get_page)(struct dpages dp,
	struct page *p, unsigned long len, unsigned *offset);
	void (next_page)(struct dpages dp);

	unsigned context_u;
	void *context_ptr;
	};

	/*
	* Functions for getting the pages from a list.
	*/
	static void list_get_page(struct dpages *dp,
	struct page *p, unsigned long len, unsigned *offset)
	{
	unsigned o = dp->context_u;
	struct page_list pl = (struct page_list ) dp->context_ptr;

	*p = pl->page;
	*len = PAGE_SIZE - o;
	*offset = o;
	}

	static void list_next_page(struct dpages *dp)
	{
	struct page_list pl = (struct page_list ) dp->context_ptr;
	dp->context_ptr = pl->next;
	dp->context_u = 0;
	}

	static void list_dp_init(struct dpages dp, struct page_list pl, unsigned offset)
	{
	dp->get_page = list_get_page;
	dp->next_page = list_next_page;
	dp->context_u = offset;
	dp->context_ptr = pl;
	}

	/*
	* Functions for getting the pages from a bvec.
	*/
	static void bvec_get_page(struct dpages *dp,
	struct page *p, unsigned long len, unsigned *offset)
	{
	struct bio_vec bvec = (struct bio_vec ) dp->context_ptr;
	*p = bvec->bv_page;
	*len = bvec->bv_len;
	*offset = bvec->bv_offset;
	}

	static void bvec_next_page(struct dpages *dp)
	{
	struct bio_vec bvec = (struct bio_vec ) dp->context_ptr;
	dp->context_ptr = bvec + 1;
	}

	static void bvec_dp_init(struct dpages dp, struct bio_vec bvec)
	{
	dp->get_page = bvec_get_page;
	dp->next_page = bvec_next_page;
	dp->context_ptr = bvec;
	}

	/*
	* Functions for getting the pages from a VMA.
	*/
	static void vm_get_page(struct dpages *dp,
	struct page *p, unsigned long len, unsigned *offset)
	{
	*p = vmalloc_to_page(dp->context_ptr);
	*offset = dp->context_u;
	*len = PAGE_SIZE - dp->context_u;
	}

	static void vm_next_page(struct dpages *dp)
	{
	dp->context_ptr += PAGE_SIZE - dp->context_u;
	dp->context_u = 0;
	}

	static void vm_dp_init(struct dpages dp, void data)
	{
	dp->get_page = vm_get_page;
	dp->next_page = vm_next_page;
	dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
	dp->context_ptr = data;
	}

	static void dm_bio_destructor(struct bio *bio)
	{
	unsigned region;
	struct io *io;

	retrieve_io_and_region_from_bio(bio, &io, &region);

	bio_free(bio, io->client->bios);
	}

	/*
	* Functions for getting the pages from kernel memory.
	*/
	static void km_get_page(struct dpages dp, struct page p, unsigned long len,
	unsigned *offset)
	{
	*p = virt_to_page(dp->context_ptr);
	*offset = dp->context_u;
	*len = PAGE_SIZE - dp->context_u;
	}

	static void km_next_page(struct dpages *dp)
	{
	dp->context_ptr += PAGE_SIZE - dp->context_u;
	dp->context_u = 0;
	}

	static void km_dp_init(struct dpages dp, void data)
	{
	dp->get_page = km_get_page;
	dp->next_page = km_next_page;
	dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
	dp->context_ptr = data;
	}

	/*-----------------------------------------------------------------
	* IO routines that accept a list of pages.
	---------------------------------------------------------------/
	static void do_region(int rw, unsigned region, struct dm_io_region *where,
	struct dpages dp, struct io io)
	{
	struct bio *bio;
	struct page *page;
	unsigned long len;
	unsigned offset;
	unsigned num_bvecs;
	sector_t remaining = where->count;

	while (remaining) {
	/*
	* Allocate a suitably sized-bio.
	*/
	num_bvecs = dm_sector_div_up(remaining,
	(PAGE_SIZE >> SECTOR_SHIFT));
	num_bvecs = min_t(int, bio_get_nr_vecs(where->bdev), num_bvecs);
	bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, io->client->bios);
	bio->bi_sector = where->sector + (where->count - remaining);
	bio->bi_bdev = where->bdev;
	bio->bi_end_io = endio;
	bio->bi_destructor = dm_bio_destructor;
	store_io_and_region_in_bio(bio, io, region);

	/*
	* Try and add as many pages as possible.
	*/
	while (remaining) {
	dp->get_page(dp, &page, &len, &offset);
	len = min(len, to_bytes(remaining));
	if (!bio_add_page(bio, page, len, offset))
	break;

	offset = 0;
	remaining -= to_sector(len);
	dp->next_page(dp);
	}

	atomic_inc(&io->count);
	submit_bio(rw, bio);
	}
	}

	static void dispatch_io(int rw, unsigned int num_regions,
	struct dm_io_region where, struct dpages dp,
	struct io *io, int sync)
	{
	int i;
	struct dpages old_pages = *dp;

	BUG_ON(num_regions > DM_IO_MAX_REGIONS);

	if (sync)
	rw \|= (1 << BIO_RW_SYNCIO) \| (1 << BIO_RW_UNPLUG);

	/*
	* For multiple regions we need to be careful to rewind
	* the dp object for each call to do_region.
	*/
	for (i = 0; i < num_regions; i++) {
	*dp = old_pages;
	if (where[i].count)
	do_region(rw, i, where + i, dp, io);
	}

	/*
	* Drop the extra reference that we were holding to avoid
	* the io being completed too early.
	*/
	dec_count(io, 0, 0);
	}

	static int sync_io(struct dm_io_client *client, unsigned int num_regions,
	struct dm_io_region where, int rw, struct dpages dp,
	unsigned long *error_bits)
	{
	/*
	* gcc <= 4.3 can't do the alignment for stack variables, so we must
	* align it on our own.
	* volatile prevents the optimizer from removing or reusing
	* "io_" field from the stack frame (allowed in ANSI C).
	*/
	volatile char io_[sizeof(struct io) + __alignof__(struct io) - 1];
	struct io io = (struct io )PTR_ALIGN(&io_, __alignof__(struct io));

	if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
	WARN_ON(1);
	return -EIO;
	}

	retry:
	io->error_bits = 0;
	io->eopnotsupp_bits = 0;
	atomic_set(&io->count, 1); /* see dispatch_io() */
	io->sleeper = current;
	io->client = client;

	dispatch_io(rw, num_regions, where, dp, io, 1);

	while (1) {
	set_current_state(TASK_UNINTERRUPTIBLE);

	if (!atomic_read(&io->count))
	break;

	io_schedule();
	}
	set_current_state(TASK_RUNNING);

	if (io->eopnotsupp_bits && (rw & (1 << BIO_RW_BARRIER))) {
	rw &= ~(1 << BIO_RW_BARRIER);
	goto retry;
	}

	if (error_bits)
	*error_bits = io->error_bits;

	return io->error_bits ? -EIO : 0;
	}

	static int async_io(struct dm_io_client *client, unsigned int num_regions,
	struct dm_io_region where, int rw, struct dpages dp,
	io_notify_fn fn, void *context)
	{
	struct io *io;

	if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
	WARN_ON(1);
	fn(1, context);
	return -EIO;
	}

	io = mempool_alloc(client->pool, GFP_NOIO);
	io->error_bits = 0;
	io->eopnotsupp_bits = 0;
	atomic_set(&io->count, 1); /* see dispatch_io() */
	io->sleeper = NULL;
	io->client = client;
	io->callback = fn;
	io->context = context;

	dispatch_io(rw, num_regions, where, dp, io, 0);
	return 0;
	}

	static int dp_init(struct dm_io_request io_req, struct dpages dp)
	{
	/* Set up dpages based on memory type */
	switch (io_req->mem.type) {
	case DM_IO_PAGE_LIST:
	list_dp_init(dp, io_req->mem.ptr.pl, io_req->mem.offset);
	break;

	case DM_IO_BVEC:
	bvec_dp_init(dp, io_req->mem.ptr.bvec);
	break;

	case DM_IO_VMA:
	vm_dp_init(dp, io_req->mem.ptr.vma);
	break;

	case DM_IO_KMEM:
	km_dp_init(dp, io_req->mem.ptr.addr);
	break;

	default:
	return -EINVAL;
	}

	return 0;
	}

	/*
	* New collapsed (a)synchronous interface.
	*
	* If the IO is asynchronous (i.e. it has notify.fn), you must either unplug
	* the queue with blk_unplug() some time later or set the BIO_RW_SYNC bit in
	* io_req->bi_rw. If you fail to do one of these, the IO will be submitted to
	* the disk after q->unplug_delay, which defaults to 3ms in blk-settings.c.
	*/
	int dm_io(struct dm_io_request *io_req, unsigned num_regions,
	struct dm_io_region where, unsigned long sync_error_bits)
	{
	int r;
	struct dpages dp;

	r = dp_init(io_req, &dp);
	if (r)
	return r;

	if (!io_req->notify.fn)
	return sync_io(io_req->client, num_regions, where,
	io_req->bi_rw, &dp, sync_error_bits);

	return async_io(io_req->client, num_regions, where, io_req->bi_rw,
	&dp, io_req->notify.fn, io_req->notify.context);
	}
	EXPORT_SYMBOL(dm_io);

	int __init dm_io_init(void)
	{
	_dm_io_cache = KMEM_CACHE(io, 0);
	if (!_dm_io_cache)
	return -ENOMEM;

	return 0;
	}

	void dm_io_exit(void)
	{
	kmem_cache_destroy(_dm_io_cache);
	_dm_io_cache = NULL;
	}