/*
 * 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;
        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 (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;

        /*
         * where->count may be zero if rw holds a flush and we need to
         * send a zero-sized flush.
         */
        do {
                /*
                 * 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);
        } while (remaining);
}

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 |= REQ_SYNC | REQ_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 || (rw & REQ_FLUSH))
                        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;
        }

        io->error_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 (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;
        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 REQ_SYNC 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;
}