text: /* bounce buffer handling for block devices
   *
   * - Split from highmem.c
   */
  
  #include <linux/mm.h>
  #include <linux/export.h>
  #include <linux/swap.h>
  #include <linux/gfp.h>
  #include <linux/bio.h>
  #include <linux/pagemap.h>
  #include <linux/mempool.h>
  #include <linux/blkdev.h>
  #include <linux/init.h>
  #include <linux/hash.h>
  #include <linux/highmem.h>
  #include <linux/bootmem.h>
  #include <asm/tlbflush.h>
  
  #include <trace/events/block.h>
  
  #define POOL_SIZE	64
  #define ISA_POOL_SIZE	16
  
  static mempool_t *page_pool, *isa_page_pool;
  
  #ifdef CONFIG_HIGHMEM
  static __init int init_emergency_pool(void)
  {
  #ifndef CONFIG_MEMORY_HOTPLUG
  	if (max_pfn <= max_low_pfn)
  		return 0;
  #endif
  
  	page_pool = mempool_create_page_pool(POOL_SIZE, 0);
  	BUG_ON(!page_pool);
  	printk("highmem bounce pool size: %d pages\n", POOL_SIZE);
  
  	return 0;
  }
  
  __initcall(init_emergency_pool);
  
  /*
   * highmem version, map in to vec
   */
  static void bounce_copy_vec(struct bio_vec *to, unsigned char *vfrom)
  {
  	unsigned long flags;
  	unsigned char *vto;
  
  	local_irq_save(flags);
  	vto = kmap_atomic(to->bv_page);
  	memcpy(vto + to->bv_offset, vfrom, to->bv_len);
  	kunmap_atomic(vto);
  	local_irq_restore(flags);
  }
  
  #else /* CONFIG_HIGHMEM */
  
  #define bounce_copy_vec(to, vfrom)	\
  	memcpy(page_address((to)->bv_page) + (to)->bv_offset, vfrom, (to)->bv_len)
  
  #endif /* CONFIG_HIGHMEM */
  
  /*
   * allocate pages in the DMA region for the ISA pool
   */
  static void *mempool_alloc_pages_isa(gfp_t gfp_mask, void *data)
  {
  	return mempool_alloc_pages(gfp_mask | GFP_DMA, data);
  }
  
  /*
   * gets called "every" time someone init's a queue with BLK_BOUNCE_ISA
   * as the max address, so check if the pool has already been created.
   */
  int init_emergency_isa_pool(void)
  {
  	if (isa_page_pool)
  		return 0;
  
  	isa_page_pool = mempool_create(ISA_POOL_SIZE, mempool_alloc_pages_isa,
  				       mempool_free_pages, (void *) 0);
  	BUG_ON(!isa_page_pool);
  
  	printk("isa bounce pool size: %d pages\n", ISA_POOL_SIZE);
  	return 0;
  }
  
  /*
   * Simple bounce buffer support for highmem pages. Depending on the
   * queue gfp mask set, *to may or may not be a highmem page. kmap it
   * always, it will do the Right Thing
   */
  static void copy_to_high_bio_irq(struct bio *to, struct bio *from)
  {
  	unsigned char *vfrom;
  	struct bio_vec *tovec, *fromvec;
  	int i;
  
  	__bio_for_each_segment(tovec, to, i, 0) {
  		fromvec = from->bi_io_vec + i;
  
  		/*
  		 * not bounced
  		 */
  		if (tovec->bv_page == fromvec->bv_page)
  			continue;
  
  		/*
  		 * fromvec->bv_offset and fromvec->bv_len might have been
  		 * modified by the block layer, so use the original copy,
  		 * bounce_copy_vec already uses tovec->bv_len
  		 */
  		vfrom = page_address(fromvec->bv_page) + tovec->bv_offset;
  
  		bounce_copy_vec(tovec, vfrom);
  		flush_dcache_page(tovec->bv_page);
  	}
  }
  
  static void bounce_end_io(struct bio *bio, mempool_t *pool, int err)
  {
  	struct bio *bio_orig = bio->bi_private;
  	struct bio_vec *bvec, *org_vec;
  	int i;
  
  	if (test_bit(BIO_EOPNOTSUPP, &bio->bi_flags))
  		set_bit(BIO_EOPNOTSUPP, &bio_orig->bi_flags);
  
  	/*
  	 * free up bounce indirect pages used
  	 */
  	__bio_for_each_segment(bvec, bio, i, 0) {
  		org_vec = bio_orig->bi_io_vec + i;
  		if (bvec->bv_page == org_vec->bv_page)
  			continue;
  
  		dec_zone_page_state(bvec->bv_page, NR_BOUNCE);
  		mempool_free(bvec->bv_page, pool);
  	}
  
  	bio_endio(bio_orig, err);
  	bio_put(bio);
  }
  
  static void bounce_end_io_write(struct bio *bio, int err)
  {
  	bounce_end_io(bio, page_pool, err);
  }
  
  static void bounce_end_io_write_isa(struct bio *bio, int err)
  {
  
  	bounce_end_io(bio, isa_page_pool, err);
  }
  
  static void __bounce_end_io_read(struct bio *bio, mempool_t *pool, int err)
  {
  	struct bio *bio_orig = bio->bi_private;
  
  	if (test_bit(BIO_UPTODATE, &bio->bi_flags))
  		copy_to_high_bio_irq(bio_orig, bio);
  
  	bounce_end_io(bio, pool, err);
  }
  
  static void bounce_end_io_read(struct bio *bio, int err)
  {
  	__bounce_end_io_read(bio, page_pool, err);
  }
  
  static void bounce_end_io_read_isa(struct bio *bio, int err)
  {
  	__bounce_end_io_read(bio, isa_page_pool, err);
  }
  
  static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
  			       mempool_t *pool)
  {
  	struct page *page;
  	struct bio *bio = NULL;
  	int i, rw = bio_data_dir(*bio_orig);
  	struct bio_vec *to, *from;
  
  	bio_for_each_segment(from, *bio_orig, i) {
  		page = from->bv_page;
  
  		/*
  		 * is destination page below bounce pfn?
  		 */
  		if (page_to_pfn(page) <= queue_bounce_pfn(q))
  			continue;
  
  		/*
  		 * irk, bounce it
  		 */
  		if (!bio) {
  			unsigned int cnt = (*bio_orig)->bi_vcnt;
  
  			bio = bio_alloc(GFP_NOIO, cnt);
  			memset(bio->bi_io_vec, 0, cnt * sizeof(struct bio_vec));
  		}
  			
  
  		to = bio->bi_io_vec + i;
  
  		to->bv_page = mempool_alloc(pool, q->bounce_gfp);
  		to->bv_len = from->bv_len;
  		to->bv_offset = from->bv_offset;
  		inc_zone_page_state(to->bv_page, NR_BOUNCE);
  
  		if (rw == WRITE) {
  			char *vto, *vfrom;
  
  			flush_dcache_page(from->bv_page);
  			vto = page_address(to->bv_page) + to->bv_offset;
  			vfrom = kmap(from->bv_page) + from->bv_offset;
  			memcpy(vto, vfrom, to->bv_len);
  			kunmap(from->bv_page);
  		}
  	}
  
  	/*
  	 * no pages bounced
  	 */
  	if (!bio)
  		return;
  
  	trace_block_bio_bounce(q, *bio_orig);
  
  	/*
  	 * at least one page was bounced, fill in possible non-highmem
  	 * pages
  	 */
  	__bio_for_each_segment(from, *bio_orig, i, 0) {
  		to = bio_iovec_idx(bio, i);
  		if (!to->bv_page) {
  			to->bv_page = from->bv_page;
  			to->bv_len = from->bv_len;
  			to->bv_offset = from->bv_offset;
  		}
  	}
  
  	bio->bi_bdev = (*bio_orig)->bi_bdev;
  	bio->bi_flags |= (1 << BIO_BOUNCED);
  	bio->bi_sector = (*bio_orig)->bi_sector;
  	bio->bi_rw = (*bio_orig)->bi_rw;
  
  	bio->bi_vcnt = (*bio_orig)->bi_vcnt;
  	bio->bi_idx = (*bio_orig)->bi_idx;
  	bio->bi_size = (*bio_orig)->bi_size;
  
  	if (pool == page_pool) {
  		bio->bi_end_io = bounce_end_io_write;
  		if (rw == READ)
  			bio->bi_end_io = bounce_end_io_read;
  	} else {
  		bio->bi_end_io = bounce_end_io_write_isa;
  		if (rw == READ)
  			bio->bi_end_io = bounce_end_io_read_isa;
  	}
  
  	bio->bi_private = *bio_orig;
  	*bio_orig = bio;
  }
  
  void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
  {
  	mempool_t *pool;
  
  	/*
  	 * Data-less bio, nothing to bounce
  	 */
  	if (!bio_has_data(*bio_orig))
  		return;
  
  	/*
  	 * for non-isa bounce case, just check if the bounce pfn is equal
  	 * to or bigger than the highest pfn in the system -- in that case,
  	 * don't waste time iterating over bio segments
  	 */
  	if (!(q->bounce_gfp & GFP_DMA)) {
  		if (queue_bounce_pfn(q) >= blk_max_pfn)
  			return;
  		pool = page_pool;
  	} else {
  		BUG_ON(!isa_page_pool);
  		pool = isa_page_pool;
  	}
  
  	/*
  	 * slow path
  	 */
  	__blk_queue_bounce(q, bio_orig, pool);
  }
  
  EXPORT_SYMBOL(blk_queue_bounce);
  