On Mon, May 11, 2015 at 02:34:55PM +0800, xuw2015@xxxxxxxxx wrote:
> From: George Wang <xuw2015@xxxxxxxxx>
>
> There are a lot of 4096 magic number in disk-io.c and volumes.c. Most of them
> are used for block size of the bdev. By the block_size(bdev) and macor
> BTRFS_MIN_BLOCK_SIZE, it can be more descriptive.
There must be some misunderstanding. Not all the 4096 constants refer to
the same thing (and for that reason a symbolic name is better).
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -2548,8 +2548,8 @@ 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_MIN_BLOCK_SIZE;
> + sb->s_blocksize_bits = blksize_bits(BTRFS_MIN_BLOCK_SIZE);
At this point in open_ctree, we're reading the superblock. Superblock
has a fixed size, defined as BTRFS_SUPER_INFO_SIZE.
s_blocksize is not used outside of the filesystem, and AFAICS unused
until we read the superblock via btrfs_read_dev_super. So at this point
it looks redundant.
> sb->s_bdi = &fs_info->bdi;
>
> btrfs_init_btree_inode(fs_info, tree_root);
> @@ -3140,11 +3140,12 @@ struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
> * later supers, using BTRFS_SUPER_MIRROR_MAX instead
> */
> for (i = 0; i < 1; i++) {
> + unsigned int blksz = block_size(bdev);
> bytenr = btrfs_sb_offset(i);
> if (bytenr + BTRFS_SUPER_INFO_SIZE >=
> i_size_read(bdev->bd_inode))
> break;
> - bh = __bread(bdev, bytenr / 4096,
> + bh = __bread(bdev, bytenr / blksz,
I think I wrote this in the first review comments, all 4096 in
btrfs_read_dev_super mean BTRFS_SUPER_INFO_SIZE. The block size is
hardcoded and not dependent on the block device.
> BTRFS_SUPER_INFO_SIZE);
> if (!bh)
> continue;
> @@ -3193,13 +3194,14 @@ static int write_dev_supers(struct btrfs_device *device,
> - bh = __find_get_block(device->bdev, bytenr / 4096,
> + bh = __find_get_block(device->bdev, bytenr / blksz,
> @@ -3229,7 +3231,7 @@ static int write_dev_supers(struct btrfs_device *device,
> - bh = __getblk(device->bdev, bytenr / 4096,
> + bh = __getblk(device->bdev, bytenr / blksz,
Same here.
> @@ -3904,13 +3906,13 @@ static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
> * The common minimum, we don't know if we can trust the nodesize/sectorsize
> * items yet, they'll be verified later. Issue just a warning.
> */
> - if (!IS_ALIGNED(btrfs_super_root(sb), 4096))
> + if (!IS_ALIGNED(btrfs_super_root(sb), BTRFS_MIN_BLOCK_SIZE))
> - if (!IS_ALIGNED(btrfs_super_chunk_root(sb), 4096))
> + if (!IS_ALIGNED(btrfs_super_chunk_root(sb), BTRFS_MIN_BLOCK_SIZE))
> - if (!IS_ALIGNED(btrfs_super_log_root(sb), 4096))
> + if (!IS_ALIGNED(btrfs_super_log_root(sb), BTRFS_MIN_BLOCK_SIZE))
> @@ -3918,14 +3920,14 @@ static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
> - if (btrfs_super_nodesize(sb) < 4096) {
> - printk(KERN_ERR "BTRFS: nodesize too small: %u < 4096\n",
> - btrfs_super_nodesize(sb));
> + if (btrfs_super_nodesize(sb) < BTRFS_MIN_BLOCK_SIZE) {
> + printk(KERN_ERR "BTRFS: nodesize too small: %u < %d\n",
> + btrfs_super_nodesize(sb), BTRFS_MIN_BLOCK_SIZE);
> - if (btrfs_super_sectorsize(sb) < 4096) {
> - printk(KERN_ERR "BTRFS: sectorsize too small: %u < 4096\n",
> - btrfs_super_sectorsize(sb));
> + if (btrfs_super_sectorsize(sb) < BTRFS_MIN_BLOCK_SIZE) {
> + printk(KERN_ERR "BTRFS: sectorsize too small: %u < %d\n",
> + btrfs_super_sectorsize(sb), BTRFS_MIN_BLOCK_SIZE);
These are correct.
> }
>
> diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
> index d4cbfee..6f43b33 100644
> --- a/fs/btrfs/disk-io.h
> +++ b/fs/btrfs/disk-io.h
> @@ -21,6 +21,7 @@
>
> #define BTRFS_SUPER_INFO_OFFSET (64 * 1024)
> #define BTRFS_SUPER_INFO_SIZE 4096
> +#define BTRFS_MIN_BLOCK_SIZE 4096
>
> #define BTRFS_SUPER_MIRROR_MAX 3
> #define BTRFS_SUPER_MIRROR_SHIFT 12
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 8bcd2a0..1f9d0de 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -200,7 +200,7 @@ 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_MIN_BLOCK_SIZE);
The set_blocksize 4096s are yet another category, that does not fit
under BTRFS_MIN_BLOCK_SIZE. The argument has other constraints like it
has to be at most a PAGE_SIZE, so the "minimal block size" does not make
sense here. See below.
> @@ -1746,14 +1746,16 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
> - bh = __bread(bdev, bytenr / 4096,
> - BTRFS_SUPER_INFO_SIZE);
> + bh = __bread(bdev, bytenr / blksz,
BTRFS_SUPER_INFO_SIZE again
> + BTRFS_SUPER_INFO_SIZE);
> if (!bh)
> continue;
>
> @@ -2167,7 +2169,7 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
> - set_blocksize(device->bdev, 4096);
> + set_blocksize(device->bdev, BTRFS_MIN_BLOCK_SIZE);
> @@ -2374,7 +2376,7 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_root *root, char *device_path,
> - set_blocksize(device->bdev, 4096);
> + set_blocksize(device->bdev, BTRFS_MIN_BLOCK_SIZE);
And set_blocksize again, so I'd say best to add another define, called
BTRFS_BDEV_BLOCK_SIZE and use it for set_blocksize.
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