/*
 * Copyright (C) 2020 Red Hat GmbH
 *
 * This file is released under the GPL.
 *
 * Device-mapper target to emulate smaller logical block
 * size on backing devices exposing (natively) larger ones.
 *
 * E.g. 512 byte sector emulation on 4K native disks.
 */

#include "dm.h"
#include <linux/module.h>
#include <linux/workqueue.h>
#include <linux/dm-bufio.h>

#define DM_MSG_PREFIX "ebs"

static void ebs_dtr(struct dm_target *ti);

/* Emulated block size context. */
struct ebs_c {
        struct dm_dev *dev;             /* Underlying device to emulate block size on. */
        struct dm_bufio_client *bufio;  /* Use dm-bufio for read and read-modify-write processing. */
        struct workqueue_struct *wq;    /* Workqueue for ^ processing of bios. */
        struct work_struct ws;          /* Work item used for ^. */
        struct bio_list bios_in;        /* Worker bios input list. */
        spinlock_t lock;                /* Guard bios input list above. */
        sector_t start;                 /* <start> table line argument, see ebs_ctr below. */
        unsigned int e_bs;              /* Emulated block size in sectors exposed to upper layer. */
        unsigned int u_bs;              /* Underlying block size in sectors retrieved from/set on lower layer device. */
        unsigned char block_shift;      /* bitshift sectors -> blocks used in dm-bufio API. */
        bool u_bs_set:1;                /* Flag to indicate underlying block size is set on table line. */
};

static inline sector_t __sector_to_block(struct ebs_c *ec, sector_t sector)
{
        return sector >> ec->block_shift;
}

static inline sector_t __block_mod(sector_t sector, unsigned int bs)
{
        return sector & (bs - 1);
}

/* Return number of blocks for a bio, accounting for misalignment of start and end sectors. */
static inline unsigned int __nr_blocks(struct ebs_c *ec, struct bio *bio)
{
        sector_t end_sector = __block_mod(bio->bi_iter.bi_sector, ec->u_bs) + bio_sectors(bio);

        return __sector_to_block(ec, end_sector) + (__block_mod(end_sector, ec->u_bs) ? 1 : 0);
}

static inline bool __ebs_check_bs(unsigned int bs)
{
        return bs && is_power_of_2(bs);
}

/*
 * READ/WRITE:
 *
 * copy blocks between bufio blocks and bio vector's (partial/overlapping) pages.
 */
static int __ebs_rw_bvec(struct ebs_c *ec, int rw, struct bio_vec *bv, struct bvec_iter *iter)
{
        int r = 0;
        unsigned char *ba, *pa;
        unsigned int cur_len;
        unsigned int bv_len = bv->bv_len;
        unsigned int buf_off = to_bytes(__block_mod(iter->bi_sector, ec->u_bs));
        sector_t block = __sector_to_block(ec, iter->bi_sector);
        struct dm_buffer *b;

        if (unlikely(!bv->bv_page || !bv_len))
                return -EIO;

        pa = bvec_virt(bv);

        /* Handle overlapping page <-> blocks */
        while (bv_len) {
                cur_len = min(dm_bufio_get_block_size(ec->bufio) - buf_off, bv_len);

                /* Avoid reading for writes in case bio vector's page overwrites block completely. */
                if (rw == READ || buf_off || bv_len < dm_bufio_get_block_size(ec->bufio))
                        ba = dm_bufio_read(ec->bufio, block, &b);
                else
                        ba = dm_bufio_new(ec->bufio, block, &b);

                if (IS_ERR(ba)) {
                        /*
                         * Carry on with next buffer, if any, to issue all possible
                         * data but return error.
                         */
                        r = PTR_ERR(ba);
                } else {
                        /* Copy data to/from bio to buffer if read/new was successful above. */
                        ba += buf_off;
                        if (rw == READ) {
                                memcpy(pa, ba, cur_len);
                                flush_dcache_page(bv->bv_page);
                        } else {
                                flush_dcache_page(bv->bv_page);
                                memcpy(ba, pa, cur_len);
                                dm_bufio_mark_partial_buffer_dirty(b, buf_off, buf_off + cur_len);
                        }

                        dm_bufio_release(b);
                }

                pa += cur_len;
                bv_len -= cur_len;
                buf_off = 0;
                block++;
        }

        return r;
}

/* READ/WRITE: iterate bio vector's copying between (partial) pages and bufio blocks. */
static int __ebs_rw_bio(struct ebs_c *ec, int rw, struct bio *bio)
{
        int r = 0, rr;
        struct bio_vec bv;
        struct bvec_iter iter;

        bio_for_each_bvec(bv, bio, iter) {
                rr = __ebs_rw_bvec(ec, rw, &bv, &iter);
                if (rr)
                        r = rr;
        }

        return r;
}

/*
 * Discard bio's blocks, i.e. pass discards down.
 *
 * Avoid discarding partial blocks at beginning and end;
 * return 0 in case no blocks can be discarded as a result.
 */
static int __ebs_discard_bio(struct ebs_c *ec, struct bio *bio)
{
        sector_t block, blocks, sector = bio->bi_iter.bi_sector;

        block = __sector_to_block(ec, sector);
        blocks = __nr_blocks(ec, bio);

        /*
         * Partial first underlying block (__nr_blocks() may have
         * resulted in one block).
         */
        if (__block_mod(sector, ec->u_bs)) {
                block++;
                blocks--;
        }

        /* Partial last underlying block if any. */
        if (blocks && __block_mod(bio_end_sector(bio), ec->u_bs))
                blocks--;

        return blocks ? dm_bufio_issue_discard(ec->bufio, block, blocks) : 0;
}

/* Release blocks them from the bufio cache. */
static void __ebs_forget_bio(struct ebs_c *ec, struct bio *bio)
{
        sector_t blocks, sector = bio->bi_iter.bi_sector;

        blocks = __nr_blocks(ec, bio);

        dm_bufio_forget_buffers(ec->bufio, __sector_to_block(ec, sector), blocks);
}

/* Worker function to process incoming bios. */
static void __ebs_process_bios(struct work_struct *ws)
{
        int r;
        bool write = false;
        sector_t block1, block2;
        struct ebs_c *ec = container_of(ws, struct ebs_c, ws);
        struct bio *bio;
        struct bio_list bios;

        bio_list_init(&bios);

        spin_lock_irq(&ec->lock);
        bios = ec->bios_in;
        bio_list_init(&ec->bios_in);
        spin_unlock_irq(&ec->lock);

        /* Prefetch all read and any mis-aligned write buffers */
        bio_list_for_each(bio, &bios) {
                block1 = __sector_to_block(ec, bio->bi_iter.bi_sector);
                if (bio_op(bio) == REQ_OP_READ)
                        dm_bufio_prefetch(ec->bufio, block1, __nr_blocks(ec, bio));
                else if (bio_op(bio) == REQ_OP_WRITE && !(bio->bi_opf & REQ_PREFLUSH)) {
                        block2 = __sector_to_block(ec, bio_end_sector(bio));
                        if (__block_mod(bio->bi_iter.bi_sector, ec->u_bs))
                                dm_bufio_prefetch(ec->bufio, block1, 1);
                        if (__block_mod(bio_end_sector(bio), ec->u_bs) && block2 != block1)
                                dm_bufio_prefetch(ec->bufio, block2, 1);
                }
        }

        bio_list_for_each(bio, &bios) {
                r = -EIO;
                if (bio_op(bio) == REQ_OP_READ)
                        r = __ebs_rw_bio(ec, READ, bio);
                else if (bio_op(bio) == REQ_OP_WRITE) {
                        write = true;
                        r = __ebs_rw_bio(ec, WRITE, bio);
                } else if (bio_op(bio) == REQ_OP_DISCARD) {
                        __ebs_forget_bio(ec, bio);
                        r = __ebs_discard_bio(ec, bio);
                }

                if (r < 0)
                        bio->bi_status = errno_to_blk_status(r);
        }

        /*
         * We write dirty buffers after processing I/O on them
         * but before we endio thus addressing REQ_FUA/REQ_SYNC.
         */
        r = write ? dm_bufio_write_dirty_buffers(ec->bufio) : 0;

        while ((bio = bio_list_pop(&bios))) {
                /* Any other request is endioed. */
                if (unlikely(r && bio_op(bio) == REQ_OP_WRITE))
                        bio_io_error(bio);
                else
                        bio_endio(bio);
        }
}

/*
 * Construct an emulated block size mapping: <dev_path> <offset> <ebs> [<ubs>]
 *
 * <dev_path>: path of the underlying device
 * <offset>: offset in 512 bytes sectors into <dev_path>
 * <ebs>: emulated block size in units of 512 bytes exposed to the upper layer
 * [<ubs>]: underlying block size in units of 512 bytes imposed on the lower layer;
 *          optional, if not supplied, retrieve logical block size from underlying device
 */
static int ebs_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
        int r;
        unsigned short tmp1;
        unsigned long long tmp;
        char dummy;
        struct ebs_c *ec;

        if (argc < 3 || argc > 4) {
                ti->error = "Invalid argument count";
                return -EINVAL;
        }

        ec = ti->private = kzalloc(sizeof(*ec), GFP_KERNEL);
        if (!ec) {
                ti->error = "Cannot allocate ebs context";
                return -ENOMEM;
        }

        r = -EINVAL;
        if (sscanf(argv[1], "%llu%c", &tmp, &dummy) != 1 ||
            tmp != (sector_t)tmp ||
            (sector_t)tmp >= ti->len) {
                ti->error = "Invalid device offset sector";
                goto bad;
        }
        ec->start = tmp;

        if (sscanf(argv[2], "%hu%c", &tmp1, &dummy) != 1 ||
            !__ebs_check_bs(tmp1) ||
            to_bytes(tmp1) > PAGE_SIZE) {
                ti->error = "Invalid emulated block size";
                goto bad;
        }
        ec->e_bs = tmp1;

        if (argc > 3) {
                if (sscanf(argv[3], "%hu%c", &tmp1, &dummy) != 1 || !__ebs_check_bs(tmp1)) {
                        ti->error = "Invalid underlying block size";
                        goto bad;
                }
                ec->u_bs = tmp1;
                ec->u_bs_set = true;
        } else
                ec->u_bs_set = false;

        r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &ec->dev);
        if (r) {
                ti->error = "Device lookup failed";
                ec->dev = NULL;
                goto bad;
        }

        r = -EINVAL;
        if (!ec->u_bs_set) {
                ec->u_bs = to_sector(bdev_logical_block_size(ec->dev->bdev));
                if (!__ebs_check_bs(ec->u_bs)) {
                        ti->error = "Invalid retrieved underlying block size";
                        goto bad;
                }
        }

        if (!ec->u_bs_set && ec->e_bs == ec->u_bs)
                DMINFO("Emulation superfluous: emulated equal to underlying block size");

        if (__block_mod(ec->start, ec->u_bs)) {
                ti->error = "Device offset must be multiple of underlying block size";
                goto bad;
        }

        ec->bufio = dm_bufio_client_create(ec->dev->bdev, to_bytes(ec->u_bs), 1, 0, NULL, NULL);
        if (IS_ERR(ec->bufio)) {
                ti->error = "Cannot create dm bufio client";
                r = PTR_ERR(ec->bufio);
                ec->bufio = NULL;
                goto bad;
        }

        ec->wq = alloc_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
        if (!ec->wq) {
                ti->error = "Cannot create dm-" DM_MSG_PREFIX " workqueue";
                r = -ENOMEM;
                goto bad;
        }

        ec->block_shift = __ffs(ec->u_bs);
        INIT_WORK(&ec->ws, &__ebs_process_bios);
        bio_list_init(&ec->bios_in);
        spin_lock_init(&ec->lock);

        ti->num_flush_bios = 1;
        ti->num_discard_bios = 1;
        ti->num_secure_erase_bios = 0;
        ti->num_write_same_bios = 0;
        ti->num_write_zeroes_bios = 0;
        return 0;
bad:
        ebs_dtr(ti);
        return r;
}

static void ebs_dtr(struct dm_target *ti)
{
        struct ebs_c *ec = ti->private;

        if (ec->wq)
                destroy_workqueue(ec->wq);
        if (ec->bufio)
                dm_bufio_client_destroy(ec->bufio);
        if (ec->dev)
                dm_put_device(ti, ec->dev);
        kfree(ec);
}

static int ebs_map(struct dm_target *ti, struct bio *bio)
{
        struct ebs_c *ec = ti->private;

        bio_set_dev(bio, ec->dev->bdev);
        bio->bi_iter.bi_sector = ec->start + dm_target_offset(ti, bio->bi_iter.bi_sector);

        if (unlikely(bio_op(bio) == REQ_OP_FLUSH))
                return DM_MAPIO_REMAPPED;
        /*
         * Only queue for bufio processing in case of partial or overlapping buffers
         * -or-
         * emulation with ebs == ubs aiming for tests of dm-bufio overhead.
         */
        if (likely(__block_mod(bio->bi_iter.bi_sector, ec->u_bs) ||
                   __block_mod(bio_end_sector(bio), ec->u_bs) ||
                   ec->e_bs == ec->u_bs)) {
                spin_lock_irq(&ec->lock);
                bio_list_add(&ec->bios_in, bio);
                spin_unlock_irq(&ec->lock);

                queue_work(ec->wq, &ec->ws);

                return DM_MAPIO_SUBMITTED;
        }

        /* Forget any buffer content relative to this direct backing device I/O. */
        __ebs_forget_bio(ec, bio);

        return DM_MAPIO_REMAPPED;
}

static void ebs_status(struct dm_target *ti, status_type_t type,
                       unsigned status_flags, char *result, unsigned maxlen)
{
        struct ebs_c *ec = ti->private;

        switch (type) {
        case STATUSTYPE_INFO:
                *result = '\0';
                break;
        case STATUSTYPE_TABLE:
                snprintf(result, maxlen, ec->u_bs_set ? "%s %llu %u %u" : "%s %llu %u",
                         ec->dev->name, (unsigned long long) ec->start, ec->e_bs, ec->u_bs);
                break;
        case STATUSTYPE_IMA:
                *result = '\0';
                break;
        }
}

static int ebs_prepare_ioctl(struct dm_target *ti, struct block_device **bdev)
{
        struct ebs_c *ec = ti->private;
        struct dm_dev *dev = ec->dev;

        /*
         * Only pass ioctls through if the device sizes match exactly.
         */
        *bdev = dev->bdev;
        return !!(ec->start || ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT);
}

static void ebs_io_hints(struct dm_target *ti, struct queue_limits *limits)
{
        struct ebs_c *ec = ti->private;

        limits->logical_block_size = to_bytes(ec->e_bs);
        limits->physical_block_size = to_bytes(ec->u_bs);
        limits->alignment_offset = limits->physical_block_size;
        blk_limits_io_min(limits, limits->logical_block_size);
}

static int ebs_iterate_devices(struct dm_target *ti,
                                  iterate_devices_callout_fn fn, void *data)
{
        struct ebs_c *ec = ti->private;

        return fn(ti, ec->dev, ec->start, ti->len, data);
}

static struct target_type ebs_target = {
        .name            = "ebs",
        .version         = {1, 0, 1},
        .features        = DM_TARGET_PASSES_INTEGRITY,
        .module          = THIS_MODULE,
        .ctr             = ebs_ctr,
        .dtr             = ebs_dtr,
        .map             = ebs_map,
        .status          = ebs_status,
        .io_hints        = ebs_io_hints,
        .prepare_ioctl   = ebs_prepare_ioctl,
        .iterate_devices = ebs_iterate_devices,
};

static int __init dm_ebs_init(void)
{
        int r = dm_register_target(&ebs_target);

        if (r < 0)
                DMERR("register failed %d", r);

        return r;
}

static void dm_ebs_exit(void)
{
        dm_unregister_target(&ebs_target);
}

module_init(dm_ebs_init);
module_exit(dm_ebs_exit);

MODULE_AUTHOR("Heinz Mauelshagen <dm-devel@redhat.com>");
MODULE_DESCRIPTION(DM_NAME " emulated block size target");
MODULE_LICENSE("GPL");