Re: [PATCH 01/12] btrfs: add definitions and constants for remap-tree

[Boris Burkov <boris@bur.io>]

On Thu, Jun 05, 2025 at 05:23:31PM +0100, Mark Harmstone wrote:
> Add an incompat flag for the new remap-tree feature, and the constants
> and definitions needed to support it.
> 
> Signed-off-by: Mark Harmstone <maharmstone@fb.com>
> ---
>  fs/btrfs/accessors.h            |  3 +++
>  fs/btrfs/sysfs.c                |  2 ++
>  fs/btrfs/tree-checker.c         |  6 ++++--
>  fs/btrfs/volumes.c              |  1 +
>  include/uapi/linux/btrfs.h      |  1 +
>  include/uapi/linux/btrfs_tree.h | 12 ++++++++++++
>  6 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/accessors.h b/fs/btrfs/accessors.h
> index 15ea6348800b..5f5eda8d6f9e 100644
> --- a/fs/btrfs/accessors.h
> +++ b/fs/btrfs/accessors.h
> @@ -1046,6 +1046,9 @@ BTRFS_SETGET_STACK_FUNCS(stack_verity_descriptor_encryption,
>  BTRFS_SETGET_STACK_FUNCS(stack_verity_descriptor_size,
>  			 struct btrfs_verity_descriptor_item, size, 64);
>  
> +BTRFS_SETGET_FUNCS(remap_address, struct btrfs_remap, address, 64);
> +BTRFS_SETGET_STACK_FUNCS(stack_remap_address, struct btrfs_remap, address, 64);
> +
>  /* Cast into the data area of the leaf. */
>  #define btrfs_item_ptr(leaf, slot, type)				\
>  	((type *)(btrfs_item_nr_offset(leaf, 0) + btrfs_item_offset(leaf, slot)))
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index f186c8082eff..831c25c2fb25 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -292,6 +292,7 @@ BTRFS_FEAT_ATTR_COMPAT_RO(free_space_tree, FREE_SPACE_TREE);
>  BTRFS_FEAT_ATTR_COMPAT_RO(block_group_tree, BLOCK_GROUP_TREE);
>  BTRFS_FEAT_ATTR_INCOMPAT(raid1c34, RAID1C34);
>  BTRFS_FEAT_ATTR_INCOMPAT(simple_quota, SIMPLE_QUOTA);
> +BTRFS_FEAT_ATTR_INCOMPAT(remap_tree, REMAP_TREE);
>  #ifdef CONFIG_BLK_DEV_ZONED
>  BTRFS_FEAT_ATTR_INCOMPAT(zoned, ZONED);
>  #endif
> @@ -326,6 +327,7 @@ static struct attribute *btrfs_supported_feature_attrs[] = {
>  	BTRFS_FEAT_ATTR_PTR(raid1c34),
>  	BTRFS_FEAT_ATTR_PTR(block_group_tree),
>  	BTRFS_FEAT_ATTR_PTR(simple_quota),
> +	BTRFS_FEAT_ATTR_PTR(remap_tree),
>  #ifdef CONFIG_BLK_DEV_ZONED
>  	BTRFS_FEAT_ATTR_PTR(zoned),
>  #endif
> diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
> index 8f4703b488b7..a83fb828723a 100644
> --- a/fs/btrfs/tree-checker.c
> +++ b/fs/btrfs/tree-checker.c
> @@ -913,11 +913,13 @@ int btrfs_check_chunk_valid(const struct btrfs_fs_info *fs_info,
>  		return -EUCLEAN;
>  	}
>  	if (unlikely(type & ~(BTRFS_BLOCK_GROUP_TYPE_MASK |
> -			      BTRFS_BLOCK_GROUP_PROFILE_MASK))) {
> +			      BTRFS_BLOCK_GROUP_PROFILE_MASK |
> +			      BTRFS_BLOCK_GROUP_REMAPPED))) {

I'm not sure when we start a mask variable for these, but probably at
least at 3 of them. Wouldn't hate one here with the second, either.

>  		chunk_err(fs_info, leaf, chunk, logical,
>  			  "unrecognized chunk type: 0x%llx",
>  			  ~(BTRFS_BLOCK_GROUP_TYPE_MASK |
> -			    BTRFS_BLOCK_GROUP_PROFILE_MASK) & type);
> +			    BTRFS_BLOCK_GROUP_PROFILE_MASK |
> +			    BTRFS_BLOCK_GROUP_REMAPPED) & type);
>  		return -EUCLEAN;
>  	}
>  
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 1535a425e8f9..3e53bde0e605 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -234,6 +234,7 @@ void btrfs_describe_block_groups(u64 bg_flags, char *buf, u32 size_buf)
>  	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_DATA, "data");
>  	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_SYSTEM, "system");
>  	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_METADATA, "metadata");
> +	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_REMAPPED, "remapped");
>  
>  	DESCRIBE_FLAG(BTRFS_AVAIL_ALLOC_BIT_SINGLE, "single");
>  	for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
> diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
> index dd02160015b2..d857cdc7694a 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -336,6 +336,7 @@ struct btrfs_ioctl_fs_info_args {
>  #define BTRFS_FEATURE_INCOMPAT_EXTENT_TREE_V2	(1ULL << 13)
>  #define BTRFS_FEATURE_INCOMPAT_RAID_STRIPE_TREE	(1ULL << 14)
>  #define BTRFS_FEATURE_INCOMPAT_SIMPLE_QUOTA	(1ULL << 16)
> +#define BTRFS_FEATURE_INCOMPAT_REMAP_TREE	(1ULL << 17)
>  
>  struct btrfs_ioctl_feature_flags {
>  	__u64 compat_flags;
> diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
> index fc29d273845d..4439d77a7252 100644
> --- a/include/uapi/linux/btrfs_tree.h
> +++ b/include/uapi/linux/btrfs_tree.h
> @@ -76,6 +76,9 @@
>  /* Tracks RAID stripes in block groups. */
>  #define BTRFS_RAID_STRIPE_TREE_OBJECTID 12ULL
>  
> +/* Holds details of remapped addresses after relocation. */
> +#define BTRFS_REMAP_TREE_OBJECTID 13ULL
> +
>  /* device stats in the device tree */
>  #define BTRFS_DEV_STATS_OBJECTID 0ULL
>  
> @@ -282,6 +285,10 @@
>  
>  #define BTRFS_RAID_STRIPE_KEY	230
>  
> +#define BTRFS_IDENTITY_REMAP_KEY 	234
> +#define BTRFS_REMAP_KEY		 	235
> +#define BTRFS_REMAP_BACKREF_KEY	 	236
> +
>  /*
>   * Records the overall state of the qgroups.
>   * There's only one instance of this key present,
> @@ -1161,6 +1168,7 @@ struct btrfs_dev_replace_item {
>  #define BTRFS_BLOCK_GROUP_RAID6         (1ULL << 8)
>  #define BTRFS_BLOCK_GROUP_RAID1C3       (1ULL << 9)
>  #define BTRFS_BLOCK_GROUP_RAID1C4       (1ULL << 10)
> +#define BTRFS_BLOCK_GROUP_REMAPPED      (1ULL << 11)
>  #define BTRFS_BLOCK_GROUP_RESERVED	(BTRFS_AVAIL_ALLOC_BIT_SINGLE | \
>  					 BTRFS_SPACE_INFO_GLOBAL_RSV)
>  
> @@ -1323,4 +1331,8 @@ struct btrfs_verity_descriptor_item {
>  	__u8 encryption;
>  } __attribute__ ((__packed__));
>  
> +struct btrfs_remap {
> +	__le64 address;

Have we ever discussed any possible future extensions or more exotic
remappings? Would any metadata about the tree or type of remapping help
with the trickier relocation issues?

> +} __attribute__ ((__packed__));
> +
>  #endif /* _BTRFS_CTREE_H_ */
> -- 
> 2.49.0
>