/*
 * Some low level IO code, and hacks for various block layer limitations
 *
 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
 * Copyright 2012 Google, Inc.
 */

#include "bcache.h"
#include "bset.h"
#include "debug.h"

#include <linux/blkdev.h>

static void bch_bi_idx_hack_endio(struct bio *bio, int error)
{
        struct bio *p = bio->bi_private;

        bio_endio(p, error);
        bio_put(bio);
}

static void bch_generic_make_request_hack(struct bio *bio)
{
        if (bio->bi_idx) {
                struct bio *clone = bio_alloc(GFP_NOIO, bio_segments(bio));

                memcpy(clone->bi_io_vec,
                       bio_iovec(bio),
                       bio_segments(bio) * sizeof(struct bio_vec));

                clone->bi_sector        = bio->bi_sector;
                clone->bi_bdev          = bio->bi_bdev;
                clone->bi_rw            = bio->bi_rw;
                clone->bi_vcnt          = bio_segments(bio);
                clone->bi_size          = bio->bi_size;

                clone->bi_private       = bio;
                clone->bi_end_io        = bch_bi_idx_hack_endio;

                bio = clone;
        }

        /*
         * Hack, since drivers that clone bios clone up to bi_max_vecs, but our
         * bios might have had more than that (before we split them per device
         * limitations).
         *
         * To be taken out once immutable bvec stuff is in.
         */
        bio->bi_max_vecs = bio->bi_vcnt;

        generic_make_request(bio);
}

/**
 * bch_bio_split - split a bio
 * @bio:        bio to split
 * @sectors:    number of sectors to split from the front of @bio
 * @gfp:        gfp mask
 * @bs:         bio set to allocate from
 *
 * Allocates and returns a new bio which represents @sectors from the start of
 * @bio, and updates @bio to represent the remaining sectors.
 *
 * If bio_sectors(@bio) was less than or equal to @sectors, returns @bio
 * unchanged.
 *
 * The newly allocated bio will point to @bio's bi_io_vec, if the split was on a
 * bvec boundry; it is the caller's responsibility to ensure that @bio is not
 * freed before the split.
 */
struct bio *bch_bio_split(struct bio *bio, int sectors,
                          gfp_t gfp, struct bio_set *bs)
{
        unsigned idx = bio->bi_idx, vcnt = 0, nbytes = sectors << 9;
        struct bio_vec *bv;
        struct bio *ret = NULL;

        BUG_ON(sectors <= 0);

        if (sectors >= bio_sectors(bio))
                return bio;

        if (bio->bi_rw & REQ_DISCARD) {
                ret = bio_alloc_bioset(gfp, 1, bs);
                if (!ret)
                        return NULL;
                idx = 0;
                goto out;
        }

        bio_for_each_segment(bv, bio, idx) {
                vcnt = idx - bio->bi_idx;

                if (!nbytes) {
                        ret = bio_alloc_bioset(gfp, vcnt, bs);
                        if (!ret)
                                return NULL;

                        memcpy(ret->bi_io_vec, bio_iovec(bio),
                               sizeof(struct bio_vec) * vcnt);

                        break;
                } else if (nbytes < bv->bv_len) {
                        ret = bio_alloc_bioset(gfp, ++vcnt, bs);
                        if (!ret)
                                return NULL;

                        memcpy(ret->bi_io_vec, bio_iovec(bio),
                               sizeof(struct bio_vec) * vcnt);

                        ret->bi_io_vec[vcnt - 1].bv_len = nbytes;
                        bv->bv_offset   += nbytes;
                        bv->bv_len      -= nbytes;
                        break;
                }

                nbytes -= bv->bv_len;
        }
out:
        ret->bi_bdev    = bio->bi_bdev;
        ret->bi_sector  = bio->bi_sector;
        ret->bi_size    = sectors << 9;
        ret->bi_rw      = bio->bi_rw;
        ret->bi_vcnt    = vcnt;
        ret->bi_max_vecs = vcnt;

        bio->bi_sector  += sectors;
        bio->bi_size    -= sectors << 9;
        bio->bi_idx      = idx;

        if (bio_integrity(bio)) {
                if (bio_integrity_clone(ret, bio, gfp)) {
                        bio_put(ret);
                        return NULL;
                }

                bio_integrity_trim(ret, 0, bio_sectors(ret));
                bio_integrity_trim(bio, bio_sectors(ret), bio_sectors(bio));
        }

        return ret;
}

static unsigned bch_bio_max_sectors(struct bio *bio)
{
        unsigned ret = bio_sectors(bio);
        struct request_queue *q = bdev_get_queue(bio->bi_bdev);
        unsigned max_segments = min_t(unsigned, BIO_MAX_PAGES,
                                      queue_max_segments(q));

        if (bio->bi_rw & REQ_DISCARD)
                return min(ret, q->limits.max_discard_sectors);

        if (bio_segments(bio) > max_segments ||
            q->merge_bvec_fn) {
                struct bio_vec *bv;
                int i, seg = 0;

                ret = 0;

                bio_for_each_segment(bv, bio, i) {
                        struct bvec_merge_data bvm = {
                                .bi_bdev        = bio->bi_bdev,
                                .bi_sector      = bio->bi_sector,
                                .bi_size        = ret << 9,
                                .bi_rw          = bio->bi_rw,
                        };

                        if (seg == max_segments)
                                break;

                        if (q->merge_bvec_fn &&
                            q->merge_bvec_fn(q, &bvm, bv) < (int) bv->bv_len)
                                break;

                        seg++;
                        ret += bv->bv_len >> 9;
                }
        }

        ret = min(ret, queue_max_sectors(q));

        WARN_ON(!ret);
        ret = max_t(int, ret, bio_iovec(bio)->bv_len >> 9);

        return ret;
}

static void bch_bio_submit_split_done(struct closure *cl)
{
        struct bio_split_hook *s = container_of(cl, struct bio_split_hook, cl);

        s->bio->bi_end_io = s->bi_end_io;
        s->bio->bi_private = s->bi_private;
        bio_endio(s->bio, 0);

        closure_debug_destroy(&s->cl);
        mempool_free(s, s->p->bio_split_hook);
}

static void bch_bio_submit_split_endio(struct bio *bio, int error)
{
        struct closure *cl = bio->bi_private;
        struct bio_split_hook *s = container_of(cl, struct bio_split_hook, cl);

        if (error)
                clear_bit(BIO_UPTODATE, &s->bio->bi_flags);

        bio_put(bio);
        closure_put(cl);
}

void bch_generic_make_request(struct bio *bio, struct bio_split_pool *p)
{
        struct bio_split_hook *s;
        struct bio *n;

        if (!bio_has_data(bio) && !(bio->bi_rw & REQ_DISCARD))
                goto submit;

        if (bio_sectors(bio) <= bch_bio_max_sectors(bio))
                goto submit;

        s = mempool_alloc(p->bio_split_hook, GFP_NOIO);
        closure_init(&s->cl, NULL);

        s->bio          = bio;
        s->p            = p;
        s->bi_end_io    = bio->bi_end_io;
        s->bi_private   = bio->bi_private;
        bio_get(bio);

        do {
                n = bch_bio_split(bio, bch_bio_max_sectors(bio),
                                  GFP_NOIO, s->p->bio_split);

                n->bi_end_io    = bch_bio_submit_split_endio;
                n->bi_private   = &s->cl;

                closure_get(&s->cl);
                bch_generic_make_request_hack(n);
        } while (n != bio);

        continue_at(&s->cl, bch_bio_submit_split_done, NULL);
submit:
        bch_generic_make_request_hack(bio);
}

/* Bios with headers */

void bch_bbio_free(struct bio *bio, struct cache_set *c)
{
        struct bbio *b = container_of(bio, struct bbio, bio);
        mempool_free(b, c->bio_meta);
}

struct bio *bch_bbio_alloc(struct cache_set *c)
{
        struct bbio *b = mempool_alloc(c->bio_meta, GFP_NOIO);
        struct bio *bio = &b->bio;

        bio_init(bio);
        bio->bi_flags           |= BIO_POOL_NONE << BIO_POOL_OFFSET;
        bio->bi_max_vecs         = bucket_pages(c);
        bio->bi_io_vec           = bio->bi_inline_vecs;

        return bio;
}

void __bch_submit_bbio(struct bio *bio, struct cache_set *c)
{
        struct bbio *b = container_of(bio, struct bbio, bio);

        bio->bi_sector  = PTR_OFFSET(&b->key, 0);
        bio->bi_bdev    = PTR_CACHE(c, &b->key, 0)->bdev;

        b->submit_time_us = local_clock_us();
        closure_bio_submit(bio, bio->bi_private, PTR_CACHE(c, &b->key, 0));
}

void bch_submit_bbio(struct bio *bio, struct cache_set *c,
                     struct bkey *k, unsigned ptr)
{
        struct bbio *b = container_of(bio, struct bbio, bio);
        bch_bkey_copy_single_ptr(&b->key, k, ptr);
        __bch_submit_bbio(bio, c);
}

/* IO errors */

void bch_count_io_errors(struct cache *ca, int error, const char *m)
{
        /*
         * The halflife of an error is:
         * log2(1/2)/log2(127/128) * refresh ~= 88 * refresh
         */

        if (ca->set->error_decay) {
                unsigned count = atomic_inc_return(&ca->io_count);

                while (count > ca->set->error_decay) {
                        unsigned errors;
                        unsigned old = count;
                        unsigned new = count - ca->set->error_decay;

                        /*
                         * First we subtract refresh from count; each time we
                         * succesfully do so, we rescale the errors once:
                         */

                        count = atomic_cmpxchg(&ca->io_count, old, new);

                        if (count == old) {
                                count = new;

                                errors = atomic_read(&ca->io_errors);
                                do {
                                        old = errors;
                                        new = ((uint64_t) errors * 127) / 128;
                                        errors = atomic_cmpxchg(&ca->io_errors,
                                                                old, new);
                                } while (old != errors);
                        }
                }
        }

        if (error) {
                char buf[BDEVNAME_SIZE];
                unsigned errors = atomic_add_return(1 << IO_ERROR_SHIFT,
                                                    &ca->io_errors);
                errors >>= IO_ERROR_SHIFT;

                if (errors < ca->set->error_limit)
                        pr_err("%s: IO error on %s, recovering",
                               bdevname(ca->bdev, buf), m);
                else
                        bch_cache_set_error(ca->set,
                                            "%s: too many IO errors %s",
                                            bdevname(ca->bdev, buf), m);
        }
}

void bch_bbio_count_io_errors(struct cache_set *c, struct bio *bio,
                              int error, const char *m)
{
        struct bbio *b = container_of(bio, struct bbio, bio);
        struct cache *ca = PTR_CACHE(c, &b->key, 0);

        unsigned threshold = bio->bi_rw & REQ_WRITE
                ? c->congested_write_threshold_us
                : c->congested_read_threshold_us;

        if (threshold) {
                unsigned t = local_clock_us();

                int us = t - b->submit_time_us;
                int congested = atomic_read(&c->congested);

                if (us > (int) threshold) {
                        int ms = us / 1024;
                        c->congested_last_us = t;

                        ms = min(ms, CONGESTED_MAX + congested);
                        atomic_sub(ms, &c->congested);
                } else if (congested < 0)
                        atomic_inc(&c->congested);
        }

        bch_count_io_errors(ca, error, m);
}

void bch_bbio_endio(struct cache_set *c, struct bio *bio,
                    int error, const char *m)
{
        struct closure *cl = bio->bi_private;

        bch_bbio_count_io_errors(c, bio, error, m);
        bio_put(bio);
        closure_put(cl);
}