+ loff_t pos, unsigned long nr_segs)
+{
+ struct inode *inode = iocb->ki_filp->f_mapping->host;
+ unsigned blkbits = blksize_bits(bdev_hardsect_size(I_BDEV(inode)));
+ unsigned blocksize_mask = (1 << blkbits) - 1;
+ unsigned long seg = 0; /* iov segment iterator */
+ unsigned long nvec; /* number of bio vec needed */
+ unsigned long cur_off; /* offset into current page */
+ unsigned long cur_len; /* I/O len of current page, up to PAGE_SIZE */
+
+ unsigned long addr; /* user iovec address */
+ size_t count; /* user iovec len */
+ size_t nbytes = iocb->ki_nbytes = iocb->ki_left; /* total xfer size */
+ loff_t size; /* size of block device */
+ struct bio *bio;
+ atomic_t *bio_count = &iocb->ki_bio_count;
+ struct page *page;
+ struct pvec pvec;
+
+ pvec.nr = 0;
+ pvec.idx = 0;
+
+ if (pos & blocksize_mask)
+ return -EINVAL;
+
+ size = i_size_read(inode);
+ if (pos + nbytes > size) {
+ nbytes = size - pos;
+ iocb->ki_left = nbytes;
+ }
+
+ /*
+ * check first non-zero iov alignment, the remaining
+ * iov alignment is checked inside bio loop below.
+ */
+ do {
+ addr = (unsigned long) iov[seg].iov_base;
+ count = min(iov[seg].iov_len, nbytes);
+ if (addr & blocksize_mask || count & blocksize_mask)
+ return -EINVAL;
+ } while (!count && ++seg < nr_segs);
+ atomic_set(bio_count, 1);
+
+ while (nbytes) {
+ /* roughly estimate number of bio vec needed */
+ nvec = (nbytes + PAGE_SIZE - 1) / PAGE_SIZE;
+ nvec = max(nvec, nr_segs - seg);
+ nvec = min(nvec, (unsigned long) BIO_MAX_PAGES);
+
+ /* bio_alloc should not fail with GFP_KERNEL flag */
+ bio = bio_alloc(GFP_KERNEL, nvec);
+ bio->bi_bdev = I_BDEV(inode);
+ bio->bi_end_io = blk_end_aio;
+ bio->bi_private = iocb;
+ bio->bi_sector = pos >> blkbits;
+same_bio:
+ cur_off = addr & ~PAGE_MASK;
+ cur_len = PAGE_SIZE - cur_off;
+ if (count < cur_len)
+ cur_len = count;
+
+ page = blk_get_page(addr, count, rw, &pvec);
+ if (unlikely(IS_ERR(page)))
+ goto backout;
+
+ if (bio_add_page(bio, page, cur_len, cur_off)) {
+ pos += cur_len;
+ addr += cur_len;
+ count -= cur_len;
+ nbytes -= cur_len;
+
+ if (count)
+ goto same_bio;
+ while (++seg < nr_segs) {
+ addr = (unsigned long) iov[seg].iov_base;
+ count = iov[seg].iov_len;
+ if (!count)
+ continue;
+ if (unlikely(addr & blocksize_mask ||
+ count & blocksize_mask)) {
+ page = ERR_PTR(-EINVAL);
+ goto backout;
+ }
+ count = min(count, nbytes);
+ goto same_bio;
+ }
+ } else {
+ blk_unget_page(page, &pvec);
+ }
+
+ /* bio is ready, submit it */
+ if (rw == READ)
+ bio_set_pages_dirty(bio);
+ atomic_inc(bio_count);
+ submit_bio(rw, bio);
+ }