btrfs: use named constant for bdev blocksize

Superblock is read and written using buffer heads, we need to set the
bdev blocksize. The magic constant has been hardcoded in several places,
so replace it with a named constant.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/check-integrity.c

@@ -795,12 +795,12 @@ static int btrfsic_process_superblock_dev_mirror(
 	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 / 4096,
+	bh = __bread(superblock_bdev, dev_bytenr / BTRFS_BDEV_BLOCKSIZE,
 		     BTRFS_SUPER_INFO_SIZE);
 	if (NULL == bh)
 		return -1;
 	super_tmp = (struct btrfs_super_block *)
-	    (bh->b_data + (dev_bytenr & 4095));
+	    (bh->b_data + (dev_bytenr & (BTRFS_BDEV_BLOCKSIZE - 1)));
 
 	if (btrfs_super_bytenr(super_tmp) != dev_bytenr ||
 	    btrfs_super_magic(super_tmp) != BTRFS_MAGIC ||
@@ -2758,7 +2758,7 @@ int btrfsic_submit_bh(int op, int op_flags, struct buffer_head *bh)
 	    (op == REQ_OP_WRITE) && bh->b_size > 0) {
 		u64 dev_bytenr;
 
-		dev_bytenr = 4096 * bh->b_blocknr;
+		dev_bytenr = BTRFS_BDEV_BLOCKSIZE * bh->b_blocknr;
 		if (dev_state->state->print_mask &
 		    BTRFSIC_PRINT_MASK_SUBMIT_BIO_BH)
 			pr_info("submit_bh(op=0x%x,0x%x, blocknr=%llu (bytenr %llu), size=%zu, data=%p, bdev=%p)\n",

fs/btrfs/disk-io.c

@@ -2694,8 +2694,8 @@ int open_ctree(struct super_block *sb,
 	btrfs_init_balance(fs_info);
 	btrfs_init_async_reclaim_work(&fs_info->async_reclaim_work);
 
-	sb->s_blocksize = 4096;
-	sb->s_blocksize_bits = blksize_bits(4096);
+	sb->s_blocksize = BTRFS_BDEV_BLOCKSIZE;
+	sb->s_blocksize_bits = blksize_bits(BTRFS_BDEV_BLOCKSIZE);
 
 	btrfs_init_btree_inode(fs_info);
 
@@ -3316,7 +3316,7 @@ int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num,
 	if (bytenr + BTRFS_SUPER_INFO_SIZE >= i_size_read(bdev->bd_inode))
 		return -EINVAL;
 
-	bh = __bread(bdev, bytenr / 4096, BTRFS_SUPER_INFO_SIZE);
+	bh = __bread(bdev, bytenr / BTRFS_BDEV_BLOCKSIZE, BTRFS_SUPER_INFO_SIZE);
 	/*
 	 * If we fail to read from the underlying devices, as of now
 	 * the best option we have is to mark it EIO.
@@ -3409,7 +3409,7 @@ static int write_dev_supers(struct btrfs_device *device,
 		btrfs_csum_final(crc, sb->csum);
 
 		/* One reference for us, and we leave it for the caller */
-		bh = __getblk(device->bdev, bytenr / 4096,
+		bh = __getblk(device->bdev, bytenr / BTRFS_BDEV_BLOCKSIZE,
 			      BTRFS_SUPER_INFO_SIZE);
 		if (!bh) {
 			btrfs_err(device->fs_info,
@@ -3468,7 +3468,8 @@ static int wait_dev_supers(struct btrfs_device *device, int max_mirrors)
 		    device->commit_total_bytes)
 			break;
 
-		bh = __find_get_block(device->bdev, bytenr / 4096,
+		bh = __find_get_block(device->bdev,
+				      bytenr / BTRFS_BDEV_BLOCKSIZE,
 				      BTRFS_SUPER_INFO_SIZE);
 		if (!bh) {
 			errors++;

fs/btrfs/disk-io.h

@@ -25,6 +25,14 @@
 #define BTRFS_SUPER_MIRROR_MAX	 3
 #define BTRFS_SUPER_MIRROR_SHIFT 12
 
+/*
+ * Fixed blocksize for all devices, applies to specific ways of reading
+ * metadata like superblock. Must meet the set_blocksize requirements.
+ *
+ * Do not change.
+ */
+#define BTRFS_BDEV_BLOCKSIZE	(4096)
+
 enum btrfs_wq_endio_type {
 	BTRFS_WQ_ENDIO_DATA = 0,
 	BTRFS_WQ_ENDIO_METADATA = 1,

fs/btrfs/volumes.c

@@ -303,7 +303,7 @@ btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
 
 	if (flush)
 		filemap_write_and_wait((*bdev)->bd_inode->i_mapping);
-	ret = set_blocksize(*bdev, 4096);
+	ret = set_blocksize(*bdev, BTRFS_BDEV_BLOCKSIZE);
 	if (ret) {
 		blkdev_put(*bdev, flags);
 		goto error;
@@ -2395,7 +2395,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 	device->is_tgtdev_for_dev_replace = 0;
 	device->mode = FMODE_EXCL;
 	device->dev_stats_valid = 1;
-	set_blocksize(device->bdev, 4096);
+	set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE);
 
 	if (seeding_dev) {
 		sb->s_flags &= ~MS_RDONLY;
@@ -2598,7 +2598,7 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
 	device->is_tgtdev_for_dev_replace = 1;
 	device->mode = FMODE_EXCL;
 	device->dev_stats_valid = 1;
-	set_blocksize(device->bdev, 4096);
+	set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE);
 	device->fs_devices = fs_info->fs_devices;
 	list_add(&device->dev_list, &fs_info->fs_devices->devices);
 	fs_info->fs_devices->num_devices++;