STRUCT ARENA_INFO(9)

💖 struct arena_info(9) — handle for an arena 💖

okay bestie, welcome to the Kernel API Manual page for struct arena_info(9) — yes, the manual name is literally right there, we’re being organized today 💅. This is the whole struct, every member, and all the little details, so let’s get into it.

🌸 NAME 🌸

struct arena_info — handle for an arena

✨ SYNOPSIS ✨

struct arena_info {
    u64 size;
    u64 external_lba_start;
    u32 internal_nlba;
    u32 internal_lbasize;
    u32 external_nlba;
    u32 external_lbasize;
    u32 nfree;
    u16 version_major;
    u16 version_minor;
    u32 sector_size;
    u64 nextoff;
    u64 infooff;
    u64 dataoff;
    u64 mapoff;
    u64 logoff;
    u64 info2off;
    struct free_entry *freelist;
    u32 *rtt;
    struct aligned_lock *map_locks;
    struct nd_btt *nd_btt;
    struct list_head list;
    struct dentry *debugfs_dir;
    u32 flags;
    struct mutex err_lock;
    int log_index[2];
};

🧚 Members 🧚

• size — Size in bytes this arena occupies on the raw device. This includes arena metadata. metadata is included, no cap.
• external_lba_start — The first external LBA in this arena.
• internal_nlba — Number of internal blocks available in the arena including nfree reserved blocks.
• internal_lbasize — Internal and external lba sizes may be different as we can round up 'odd' external lbasizes such as 520B to be aligned.
• external_nlba — Number of blocks contributed by the arena to the number reported to upper layers. (internal_nlba - nfree)
• external_lbasize — LBA size as exposed to upper layers.
• nfree — A reserve number of 'free' blocks that is used to handle incoming writes.
• version_major — Metadata layout version major.
• version_minor — Metadata layout version minor.
• sector_size — The Linux sector size - 512 or 4096.
• nextoff — Offset in bytes to the start of the next arena.
• infooff — Offset in bytes to the info block of this arena.
• dataoff — Offset in bytes to the data area of this arena.
• mapoff — Offset in bytes to the map area of this arena.
• logoff — Offset in bytes to the log area of this arena.
• info2off — Offset in bytes to the backup info block of this arena.
• freelist — Pointer to in-memory list of free blocks.
• rtt — Pointer to in-memory "Read Tracking Table".
• map_locks — Spinlocks protecting concurrent map writes.
• nd_btt — Pointer to parent nd_btt structure.
• list — List head for list of arenas.
• debugfs_dir — Debugfs dentry.
• flags — Arena flags - may signify error states.
• err_lock — Mutex for synchronizing error clearing.
• log_index — Indices of the valid log entries in a log_group.

💖 Description 💖

arena_info is a per-arena handle. Once an arena is narrowed down for an IO, this struct is passed around for the duration of the IO. it’s giving “main character struct” for exactly one IO’s journey 🦋.

🦋 SEE ALSO 🦋

Kernel file ./drivers/nvdimm/btt.h and struct btt(9) — go read those too, bestie 👀.

with love and zero missing fields, your kernel group chat 💅✨ — source/version: ./drivers/nvdimm, date: October 2026, and yeah, the manual name is struct arena_info(9) 🎀.