[PATCH v7 8/8] btrfs: remove buffer_heads form superblock mirror integrity checking

[Johannes Thumshirn <johannes.thumshirn@wdc.com>]

The integrity checking code for the superblock mirrors is the last remaining
user of buffer_heads in BTRFS, change it to using plain BIOs as well.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>

---
Changes to v4:
- Remove mapping_gfp_constraint()

Changes to v2:
- Open-code kunmap() + put_page() (David)
- Remove __GFP_NOFAIL from allocation (Josef)
- Merge error paths (David)

Changes to v1:
- Convert from alloc_page() to find_or_create_page()
---
 fs/btrfs/check-integrity.c | 55 +++++++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index 4f6db2fe482a..e10a27d6db08 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -77,7 +77,6 @@
 
 #include <linux/sched.h>
 #include <linux/slab.h>
-#include <linux/buffer_head.h>
 #include <linux/mutex.h>
 #include <linux/genhd.h>
 #include <linux/blkdev.h>
@@ -762,29 +761,45 @@ static int btrfsic_process_superblock_dev_mirror(
 	struct btrfs_fs_info *fs_info = state->fs_info;
 	struct btrfs_super_block *super_tmp;
 	u64 dev_bytenr;
-	struct buffer_head *bh;
 	struct btrfsic_block *superblock_tmp;
 	int pass;
 	struct block_device *const superblock_bdev = device->bdev;
+	struct page *page;
+	struct bio bio;
+	struct bio_vec bio_vec;
+	struct address_space *mapping = superblock_bdev->bd_inode->i_mapping;
+	int ret;
 
 	/* super block bytenr is always the unmapped device bytenr */
 	dev_bytenr = btrfs_sb_offset(superblock_mirror_num);
 	if (dev_bytenr + BTRFS_SUPER_INFO_SIZE > device->commit_total_bytes)
 		return -1;
-	bh = __bread(superblock_bdev, dev_bytenr / BTRFS_BDEV_BLOCKSIZE,
-		     BTRFS_SUPER_INFO_SIZE);
-	if (NULL == bh)
+
+	page = find_or_create_page(mapping, dev_bytenr >> PAGE_SHIFT, GFP_NOFS);
+	if (!page)
+		return -1;
+
+	bio_init(&bio, &bio_vec, 1);
+	bio.bi_iter.bi_sector = dev_bytenr >> SECTOR_SHIFT;
+	bio_set_dev(&bio, superblock_bdev);
+	bio_set_op_attrs(&bio, REQ_OP_READ, 0);
+	bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE, 0);
+
+	ret = submit_bio_wait(&bio);
+	if (ret)
 		return -1;
-	super_tmp = (struct btrfs_super_block *)
-	    (bh->b_data + (dev_bytenr & (BTRFS_BDEV_BLOCKSIZE - 1)));
+
+	unlock_page(page);
+
+	super_tmp = kmap(page);
 
 	if (btrfs_super_bytenr(super_tmp) != dev_bytenr ||
 	    btrfs_super_magic(super_tmp) != BTRFS_MAGIC ||
 	    memcmp(device->uuid, super_tmp->dev_item.uuid, BTRFS_UUID_SIZE) ||
 	    btrfs_super_nodesize(super_tmp) != state->metablock_size ||
 	    btrfs_super_sectorsize(super_tmp) != state->datablock_size) {
-		brelse(bh);
-		return 0;
+		ret = 0;
+		goto out_unmap;
 	}
 
 	superblock_tmp =
@@ -795,8 +810,8 @@ static int btrfsic_process_superblock_dev_mirror(
 		superblock_tmp = btrfsic_block_alloc();
 		if (NULL == superblock_tmp) {
 			pr_info("btrfsic: error, kmalloc failed!\n");
-			brelse(bh);
-			return -1;
+			ret = -1;
+			goto out_unmap;
 		}
 		/* for superblock, only the dev_bytenr makes sense */
 		superblock_tmp->dev_bytenr = dev_bytenr;
@@ -880,8 +895,8 @@ static int btrfsic_process_superblock_dev_mirror(
 					      mirror_num)) {
 				pr_info("btrfsic: btrfsic_map_block(bytenr @%llu, mirror %d) failed!\n",
 				       next_bytenr, mirror_num);
-				brelse(bh);
-				return -1;
+				ret = -1;
+				goto out_unmap;
 			}
 
 			next_block = btrfsic_block_lookup_or_add(
@@ -890,8 +905,8 @@ static int btrfsic_process_superblock_dev_mirror(
 					mirror_num, NULL);
 			if (NULL == next_block) {
 				btrfsic_release_block_ctx(&tmp_next_block_ctx);
-				brelse(bh);
-				return -1;
+				ret = -1;
+				goto out_unmap;
 			}
 
 			next_block->disk_key = tmp_disk_key;
@@ -902,16 +917,18 @@ static int btrfsic_process_superblock_dev_mirror(
 					BTRFSIC_GENERATION_UNKNOWN);
 			btrfsic_release_block_ctx(&tmp_next_block_ctx);
 			if (NULL == l) {
-				brelse(bh);
-				return -1;
+				ret = -1;
+				goto out_unmap;
 			}
 		}
 	}
 	if (state->print_mask & BTRFSIC_PRINT_MASK_INITIAL_ALL_TREES)
 		btrfsic_dump_tree_sub(state, superblock_tmp, 0);
 
-	brelse(bh);
-	return 0;
+out_unmap:
+	kunmap(page);
+	put_page(page);
+	return ret;
 }
 
 static struct btrfsic_stack_frame *btrfsic_stack_frame_alloc(void)
-- 
2.24.1