![Mikulas Patocka](/assets/img/avatar_default.png)
Remove an avoidable 3ms delay on some dm-raid1 and kcopyd I/O. It is specified that any submitted bio without BIO_RW_SYNC flag may plug the queue (i.e. block the requests from being dispatched to the physical device). The queue is unplugged when the caller calls blk_unplug() function. Usually, the sequence is that someone calls submit_bh to submit IO on a buffer. The IO plugs the queue and waits (to be possibly joined with other adjacent bios). Then, when the caller calls wait_on_buffer(), it unplugs the queue and submits the IOs to the disk. This was happenning: When doing O_SYNC writes, function fsync_buffers_list() submits a list of bios to dm_raid1, the bios are added to dm_raid1 write queue and kmirrord is woken up. fsync_buffers_list() calls wait_on_buffer(). That unplugs the queue, but there are no bios on the device queue as they are still in the dm_raid1 queue. wait_on_buffer() starts waiting until the IO is finished. kmirrord is scheduled, kmirrord takes bios and submits them to the devices. The submitted bio plugs the harddisk queue but there is no one to unplug it. (The process that called wait_on_buffer() is already sleeping.) So there is a 3ms timeout, after which the queues on the harddisks are unplugged and requests are processed. This 3ms timeout meant that in certain workloads (e.g. O_SYNC, 8kb writes), dm-raid1 is 10 times slower than md raid1. Every time we submit something asynchronously via dm_io, we must unplug the queue actually to send the request to the device. This patch adds an unplug call to kmirrord - while processing requests, it keeps the queue plugged (so that adjacent bios can be merged); when it finishes processing all the bios, it unplugs the queue to submit the bios. It also fixes kcopyd which has the same potential problem. All kcopyd requests are submitted with BIO_RW_SYNC. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> Acked-by: Jens Axboe <jens.axboe@oracle.com>
464 lines
11 KiB
C
464 lines
11 KiB
C
/*
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* Copyright (C) 2003 Sistina Software
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* Copyright (C) 2006 Red Hat GmbH
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*
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* This file is released under the GPL.
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*/
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#include "dm.h"
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#include <linux/bio.h>
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#include <linux/mempool.h>
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/dm-io.h>
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struct dm_io_client {
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mempool_t *pool;
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struct bio_set *bios;
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};
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/* FIXME: can we shrink this ? */
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struct io {
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unsigned long error_bits;
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atomic_t count;
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struct task_struct *sleeper;
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struct dm_io_client *client;
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io_notify_fn callback;
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void *context;
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};
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/*
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* io contexts are only dynamically allocated for asynchronous
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* io. Since async io is likely to be the majority of io we'll
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* have the same number of io contexts as bios! (FIXME: must reduce this).
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*/
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static unsigned int pages_to_ios(unsigned int pages)
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{
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return 4 * pages; /* too many ? */
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}
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/*
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* Create a client with mempool and bioset.
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*/
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struct dm_io_client *dm_io_client_create(unsigned num_pages)
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{
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unsigned ios = pages_to_ios(num_pages);
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struct dm_io_client *client;
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client = kmalloc(sizeof(*client), GFP_KERNEL);
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if (!client)
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return ERR_PTR(-ENOMEM);
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client->pool = mempool_create_kmalloc_pool(ios, sizeof(struct io));
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if (!client->pool)
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goto bad;
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client->bios = bioset_create(16, 16);
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if (!client->bios)
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goto bad;
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return client;
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bad:
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if (client->pool)
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mempool_destroy(client->pool);
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kfree(client);
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return ERR_PTR(-ENOMEM);
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}
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EXPORT_SYMBOL(dm_io_client_create);
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int dm_io_client_resize(unsigned num_pages, struct dm_io_client *client)
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{
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return mempool_resize(client->pool, pages_to_ios(num_pages),
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GFP_KERNEL);
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}
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EXPORT_SYMBOL(dm_io_client_resize);
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void dm_io_client_destroy(struct dm_io_client *client)
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{
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mempool_destroy(client->pool);
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bioset_free(client->bios);
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kfree(client);
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}
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EXPORT_SYMBOL(dm_io_client_destroy);
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/*-----------------------------------------------------------------
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* We need to keep track of which region a bio is doing io for.
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* In order to save a memory allocation we store this the last
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* bvec which we know is unused (blech).
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* XXX This is ugly and can OOPS with some configs... find another way.
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*---------------------------------------------------------------*/
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static inline void bio_set_region(struct bio *bio, unsigned region)
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{
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bio->bi_io_vec[bio->bi_max_vecs].bv_len = region;
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}
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static inline unsigned bio_get_region(struct bio *bio)
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{
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return bio->bi_io_vec[bio->bi_max_vecs].bv_len;
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}
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/*-----------------------------------------------------------------
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* We need an io object to keep track of the number of bios that
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* have been dispatched for a particular io.
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*---------------------------------------------------------------*/
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static void dec_count(struct io *io, unsigned int region, int error)
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{
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if (error)
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set_bit(region, &io->error_bits);
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if (atomic_dec_and_test(&io->count)) {
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if (io->sleeper)
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wake_up_process(io->sleeper);
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else {
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unsigned long r = io->error_bits;
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io_notify_fn fn = io->callback;
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void *context = io->context;
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mempool_free(io, io->client->pool);
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fn(r, context);
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}
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}
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}
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static void endio(struct bio *bio, int error)
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{
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struct io *io;
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unsigned region;
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if (error && bio_data_dir(bio) == READ)
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zero_fill_bio(bio);
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/*
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* The bio destructor in bio_put() may use the io object.
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*/
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io = bio->bi_private;
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region = bio_get_region(bio);
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bio->bi_max_vecs++;
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bio_put(bio);
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dec_count(io, region, error);
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}
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/*-----------------------------------------------------------------
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* These little objects provide an abstraction for getting a new
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* destination page for io.
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*---------------------------------------------------------------*/
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struct dpages {
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void (*get_page)(struct dpages *dp,
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struct page **p, unsigned long *len, unsigned *offset);
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void (*next_page)(struct dpages *dp);
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unsigned context_u;
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void *context_ptr;
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};
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/*
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* Functions for getting the pages from a list.
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*/
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static void list_get_page(struct dpages *dp,
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struct page **p, unsigned long *len, unsigned *offset)
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{
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unsigned o = dp->context_u;
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struct page_list *pl = (struct page_list *) dp->context_ptr;
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*p = pl->page;
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*len = PAGE_SIZE - o;
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*offset = o;
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}
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static void list_next_page(struct dpages *dp)
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{
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struct page_list *pl = (struct page_list *) dp->context_ptr;
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dp->context_ptr = pl->next;
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dp->context_u = 0;
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}
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static void list_dp_init(struct dpages *dp, struct page_list *pl, unsigned offset)
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{
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dp->get_page = list_get_page;
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dp->next_page = list_next_page;
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dp->context_u = offset;
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dp->context_ptr = pl;
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}
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/*
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* Functions for getting the pages from a bvec.
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*/
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static void bvec_get_page(struct dpages *dp,
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struct page **p, unsigned long *len, unsigned *offset)
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{
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struct bio_vec *bvec = (struct bio_vec *) dp->context_ptr;
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*p = bvec->bv_page;
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*len = bvec->bv_len;
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*offset = bvec->bv_offset;
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}
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static void bvec_next_page(struct dpages *dp)
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{
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struct bio_vec *bvec = (struct bio_vec *) dp->context_ptr;
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dp->context_ptr = bvec + 1;
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}
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static void bvec_dp_init(struct dpages *dp, struct bio_vec *bvec)
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{
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dp->get_page = bvec_get_page;
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dp->next_page = bvec_next_page;
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dp->context_ptr = bvec;
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}
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/*
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* Functions for getting the pages from a VMA.
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*/
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static void vm_get_page(struct dpages *dp,
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struct page **p, unsigned long *len, unsigned *offset)
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{
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*p = vmalloc_to_page(dp->context_ptr);
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*offset = dp->context_u;
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*len = PAGE_SIZE - dp->context_u;
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}
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static void vm_next_page(struct dpages *dp)
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{
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dp->context_ptr += PAGE_SIZE - dp->context_u;
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dp->context_u = 0;
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}
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static void vm_dp_init(struct dpages *dp, void *data)
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{
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dp->get_page = vm_get_page;
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dp->next_page = vm_next_page;
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dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
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dp->context_ptr = data;
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}
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static void dm_bio_destructor(struct bio *bio)
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{
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struct io *io = bio->bi_private;
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bio_free(bio, io->client->bios);
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}
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/*
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* Functions for getting the pages from kernel memory.
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*/
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static void km_get_page(struct dpages *dp, struct page **p, unsigned long *len,
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unsigned *offset)
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{
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*p = virt_to_page(dp->context_ptr);
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*offset = dp->context_u;
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*len = PAGE_SIZE - dp->context_u;
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}
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static void km_next_page(struct dpages *dp)
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{
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dp->context_ptr += PAGE_SIZE - dp->context_u;
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dp->context_u = 0;
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}
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static void km_dp_init(struct dpages *dp, void *data)
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{
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dp->get_page = km_get_page;
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dp->next_page = km_next_page;
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dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
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dp->context_ptr = data;
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}
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/*-----------------------------------------------------------------
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* IO routines that accept a list of pages.
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*---------------------------------------------------------------*/
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static void do_region(int rw, unsigned region, struct dm_io_region *where,
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struct dpages *dp, struct io *io)
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{
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struct bio *bio;
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struct page *page;
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unsigned long len;
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unsigned offset;
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unsigned num_bvecs;
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sector_t remaining = where->count;
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while (remaining) {
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/*
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* Allocate a suitably sized-bio: we add an extra
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* bvec for bio_get/set_region() and decrement bi_max_vecs
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* to hide it from bio_add_page().
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*/
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num_bvecs = dm_sector_div_up(remaining,
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(PAGE_SIZE >> SECTOR_SHIFT));
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num_bvecs = 1 + min_t(int, bio_get_nr_vecs(where->bdev),
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num_bvecs);
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bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, io->client->bios);
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bio->bi_sector = where->sector + (where->count - remaining);
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bio->bi_bdev = where->bdev;
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bio->bi_end_io = endio;
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bio->bi_private = io;
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bio->bi_destructor = dm_bio_destructor;
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bio->bi_max_vecs--;
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bio_set_region(bio, region);
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/*
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* Try and add as many pages as possible.
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*/
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while (remaining) {
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dp->get_page(dp, &page, &len, &offset);
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len = min(len, to_bytes(remaining));
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if (!bio_add_page(bio, page, len, offset))
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break;
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offset = 0;
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remaining -= to_sector(len);
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dp->next_page(dp);
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}
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atomic_inc(&io->count);
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submit_bio(rw, bio);
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}
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}
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static void dispatch_io(int rw, unsigned int num_regions,
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struct dm_io_region *where, struct dpages *dp,
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struct io *io, int sync)
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{
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int i;
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struct dpages old_pages = *dp;
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if (sync)
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rw |= (1 << BIO_RW_SYNC);
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/*
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* For multiple regions we need to be careful to rewind
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* the dp object for each call to do_region.
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*/
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for (i = 0; i < num_regions; i++) {
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*dp = old_pages;
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if (where[i].count)
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do_region(rw, i, where + i, dp, io);
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}
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/*
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* Drop the extra reference that we were holding to avoid
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* the io being completed too early.
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*/
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dec_count(io, 0, 0);
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}
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static int sync_io(struct dm_io_client *client, unsigned int num_regions,
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struct dm_io_region *where, int rw, struct dpages *dp,
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unsigned long *error_bits)
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{
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struct io io;
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if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
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WARN_ON(1);
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return -EIO;
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}
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io.error_bits = 0;
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atomic_set(&io.count, 1); /* see dispatch_io() */
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io.sleeper = current;
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io.client = client;
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dispatch_io(rw, num_regions, where, dp, &io, 1);
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while (1) {
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set_current_state(TASK_UNINTERRUPTIBLE);
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if (!atomic_read(&io.count) || signal_pending(current))
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break;
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io_schedule();
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}
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set_current_state(TASK_RUNNING);
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if (atomic_read(&io.count))
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return -EINTR;
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if (error_bits)
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*error_bits = io.error_bits;
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return io.error_bits ? -EIO : 0;
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}
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static int async_io(struct dm_io_client *client, unsigned int num_regions,
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struct dm_io_region *where, int rw, struct dpages *dp,
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io_notify_fn fn, void *context)
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{
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struct io *io;
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if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
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WARN_ON(1);
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fn(1, context);
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return -EIO;
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}
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io = mempool_alloc(client->pool, GFP_NOIO);
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io->error_bits = 0;
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atomic_set(&io->count, 1); /* see dispatch_io() */
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io->sleeper = NULL;
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io->client = client;
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io->callback = fn;
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io->context = context;
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dispatch_io(rw, num_regions, where, dp, io, 0);
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return 0;
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}
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static int dp_init(struct dm_io_request *io_req, struct dpages *dp)
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{
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/* Set up dpages based on memory type */
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switch (io_req->mem.type) {
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case DM_IO_PAGE_LIST:
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list_dp_init(dp, io_req->mem.ptr.pl, io_req->mem.offset);
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break;
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case DM_IO_BVEC:
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bvec_dp_init(dp, io_req->mem.ptr.bvec);
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break;
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case DM_IO_VMA:
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vm_dp_init(dp, io_req->mem.ptr.vma);
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break;
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case DM_IO_KMEM:
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km_dp_init(dp, io_req->mem.ptr.addr);
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break;
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default:
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return -EINVAL;
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}
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return 0;
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}
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/*
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* New collapsed (a)synchronous interface.
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*
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* If the IO is asynchronous (i.e. it has notify.fn), you must either unplug
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* the queue with blk_unplug() some time later or set the BIO_RW_SYNC bit in
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* io_req->bi_rw. If you fail to do one of these, the IO will be submitted to
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* the disk after q->unplug_delay, which defaults to 3ms in blk-settings.c.
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*/
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int dm_io(struct dm_io_request *io_req, unsigned num_regions,
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struct dm_io_region *where, unsigned long *sync_error_bits)
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{
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int r;
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struct dpages dp;
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r = dp_init(io_req, &dp);
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if (r)
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return r;
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if (!io_req->notify.fn)
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return sync_io(io_req->client, num_regions, where,
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io_req->bi_rw, &dp, sync_error_bits);
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return async_io(io_req->client, num_regions, where, io_req->bi_rw,
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&dp, io_req->notify.fn, io_req->notify.context);
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}
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EXPORT_SYMBOL(dm_io);
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