text: // SPDX-License-Identifier: GPL-2.0
  /*
   * Copyright (c) 2019 Christoph Hellwig.
   */
  #include "xfs.h"
  
  static inline unsigned int bio_max_vecs(unsigned int count)
  {
  	return bio_max_segs(howmany(count, PAGE_SIZE));
  }
  
  static void
  xfs_flush_bdev_async_endio(
  	struct bio	*bio)
  {
  	complete(bio->bi_private);
  }
  
  /*
   * Submit a request for an async cache flush to run. If the request queue does
   * not require flush operations, just skip it altogether. If the caller needs
   * to wait for the flush completion at a later point in time, they must supply a
   * valid completion. This will be signalled when the flush completes.  The
   * caller never sees the bio that is issued here.
   */
  void
  xfs_flush_bdev_async(
  	struct bio		*bio,
  	struct block_device	*bdev,
  	struct completion	*done)
  {
  	struct request_queue	*q = bdev->bd_disk->queue;
  
  	if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
  		complete(done);
  		return;
  	}
  
  	bio_init(bio, NULL, 0);
  	bio_set_dev(bio, bdev);
  	bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC;
  	bio->bi_private = done;
  	bio->bi_end_io = xfs_flush_bdev_async_endio;
  
  	submit_bio(bio);
  }
  int
  xfs_rw_bdev(
  	struct block_device	*bdev,
  	sector_t		sector,
  	unsigned int		count,
  	char			*data,
  	unsigned int		op)
  
  {
  	unsigned int		is_vmalloc = is_vmalloc_addr(data);
  	unsigned int		left = count;
  	int			error;
  	struct bio		*bio;
  
  	if (is_vmalloc && op == REQ_OP_WRITE)
  		flush_kernel_vmap_range(data, count);
  
  	bio = bio_alloc(GFP_KERNEL, bio_max_vecs(left));
  	bio_set_dev(bio, bdev);
  	bio->bi_iter.bi_sector = sector;
  	bio->bi_opf = op | REQ_META | REQ_SYNC;
  
  	do {
  		struct page	*page = kmem_to_page(data);
  		unsigned int	off = offset_in_page(data);
  		unsigned int	len = min_t(unsigned, left, PAGE_SIZE - off);
  
  		while (bio_add_page(bio, page, len, off) != len) {
  			struct bio	*prev = bio;
  
  			bio = bio_alloc(GFP_KERNEL, bio_max_vecs(left));
  			bio_copy_dev(bio, prev);
  			bio->bi_iter.bi_sector = bio_end_sector(prev);
  			bio->bi_opf = prev->bi_opf;
  			bio_chain(prev, bio);
  
  			submit_bio(prev);
  		}
  
  		data += len;
  		left -= len;
  	} while (left > 0);
  
  	error = submit_bio_wait(bio);
  	bio_put(bio);
  
  	if (is_vmalloc && op == REQ_OP_READ)
  		invalidate_kernel_vmap_range(data, count);
  	return error;
  }
  