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struct buffer_head { 

    unsigned long b_state; /* buffer state bitmap (see above) */

    struct buffer_head *b_this_page; /* circular list of page's buffers */

    struct page *b_page;  /* the page this bh is mapped to */

    sector_t b_blocknr;                          /* start block number */

    size_t b_size;                                   /* size of mapping */

    char *b_data;             /* pointer to data within the page */

   struct block_device *b_bdev;

   bh_end_io_t *b_end_io;                   /* I/O completion */

  void *b_private;                              /* reserved for b_end_io */

  struct list_head b_assoc_buffers;     /* associated with another mapping */

  struct address_space *b_assoc_map;    /* mapping this buffer is

                                                             associated with */

   atomic_t b_count;                          /* users using this buffer_head */

};

void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])

{

    int i;

    for (i = 0; i < nr; i ) {

        struct buffer_head *bh = bhs[i];

        if (!trylock_buffer(bh))

            continue;

        if (rw == WRITE) {

            if (test_clear_buffer_dirty(bh)) {

                bh->b_end_io = end_buffer_write_sync;

                get_bh(bh);

                submit_bh(WRITE, bh);

                continue;

            }

        } else {

            if (!buffer_uptodate(bh)) {

                bh->b_end_io = end_buffer_read_sync;

                get_bh(bh);

                submit_bh(rw, bh);

                continue;

            }

        }

        unlock_buffer(bh);

    }

}

int submit_bh(int rw, struct buffer_head * bh)

{

    struct bio *bio;

    int ret = 0;

    BUG_ON(!buffer_locked(bh));

    BUG_ON(!buffer_mapped(bh));

    BUG_ON(!bh->b_end_io);

    BUG_ON(buffer_delay(bh));

    BUG_ON(buffer_unwritten(bh));

    /*

     * Only clear out a write error when rewriting

     */

    if (test_set_buffer_req(bh) && (rw & WRITE))

        clear_buffer_write_io_error(bh);

    /*

     * from here on down, it's all bio -- do the initial mapping,

     * submit_bio -> generic_make_request may further map this bio around

     */

    bio = bio_alloc(GFP_NOIO, 1);

    bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);

    bio->bi_bdev = bh->b_bdev;

    bio->bi_io_vec[].bv_page = bh->b_page;

    bio->bi_io_vec[].bv_len = bh->b_size;

    bio->bi_io_vec[].bv_offset = bh_offset(bh);

    bio->bi_vcnt = 1;

    bio->bi_idx = 0;

    bio->bi_size = bh->b_size;

    bio->bi_end_io = end_bio_bh_io_sync;

    bio->bi_private = bh;

    bio_get(bio);

    submit_bio(rw, bio);

    if (bio_flagged(bio, BIO_EOPNOTSUPP))

        ret = -EOPNOTSUPP;

    bio_put(bio);

    return ret;

}

void generic_make_request(struct bio *bio)

{

    struct bio_list bio_list_on_stack;

    if (!generic_make_request_checks(bio))

        return;

    if (current->bio_list) {

        bio_list_add(current->bio_list, bio);

        return;

    }

    BUG_ON(bio->bi_next);

    bio_list_init(&bio_list_on_stack);

    current->bio_list = &bio_list_on_stack;

    do {

        struct request_queue *q = bdev_get_queue(bio->bi_bdev);

        q->make_request_fn(q, bio);

        bio = bio_list_pop(current->bio_list);

    } while (bio);

    current->bio_list = NULL; /* deactivate */

}