STRUCT UBIFS_SB_NODE(9)

💖 struct ubifs_sb_node(9) — the superblock node, bestie 💖

okay so this is a page from the Kernel API Manual, and it's literally all about struct ubifs_sb_node — the superblock node. that's it, that's the whole vibe. it's giving "the main character of your UBIFS filesystem's metadata" 👑

✨ SYNOPSIS ✨

here's the whole struct, copied exactly, no notes:

struct ubifs_sb_node {
    struct ubifs_ch ch;
    __u8 padding[2];
    __u8 key_hash;
    __u8 key_fmt;
    __le32 flags;
    __le32 min_io_size;
    __le32 leb_size;
    __le32 leb_cnt;
    __le32 max_leb_cnt;
    __le64 max_bud_bytes;
    __le32 log_lebs;
    __le32 lpt_lebs;
    __le32 orph_lebs;
    __le32 jhead_cnt;
    __le32 fanout;
    __le32 lsave_cnt;
    __le32 fmt_version;
    __le16 default_compr;
    __u8 padding1[2];
    __le32 rp_uid;
    __le32 rp_gid;
    __le64 rp_size;
    __le32 time_gran;
    __u8 uuid[16];
    __le32 ro_compat_version;
    __u8 hmac[UBIFS_MAX_HMAC_LEN];
    __u8 hmac_wkm[UBIFS_MAX_HMAC_LEN];
    __le16 hash_algo;
    __u8 hash_mst[UBIFS_MAX_HASH_LEN];
    __u8 padding2[3774];
};

slay. now let's meet the members one by one, they all have main character energy in their own way 🫶

🌸 Members 🌸

• ch — the common header. every struct needs a little hello.
• padding — reserved for future, zeroes. it's just vibing, holding space 💅
• key_hash — the type of hash function used in keys.
• key_fmt — the format of the key.
• flags — file-system flags (UBIFS_FLG_BIGLPT, etc). yes there are more, this is just the example, iykyk.
• min_io_size — minimal input/output unit size.
• leb_size — logical eraseblock size in bytes.
• leb_cnt — count of LEBs used by the file-system.
• max_leb_cnt — maximum count of LEBs used by the file-system. the ceiling, the limit, the "don't push it" ✋
• max_bud_bytes — maximum amount of data stored in buds.
• log_lebs — log size in logical eraseblocks.
• lpt_lebs — number of LEBs used for the lprops table.
• orph_lebs — number of LEBs used for recording orphans. 🥺 they're not really orphans, they're just between parents rn.
• jhead_cnt — count of journal heads.
• fanout — tree fanout (max. number of links per indexing node).
• lsave_cnt — number of LEB numbers in LPT's save table.
• fmt_version — UBIFS on-flash format version.
• default_compr — default compression algorithm (UBIFS_COMPR_LZO, etc). squish it, bestie 🗜️
• padding1 — reserved for future, zeroes. second reserved block, still zeroes, still chillin'.
• rp_uid — reserve pool UID.
• rp_gid — reserve pool GID.
• rp_size — size of the reserved pool in bytes.
• time_gran — time granularity in nanoseconds. tiny tiny time baby ⏱️
• uuid — UUID generated when the file system image was created. its little birth certificate 🎀
• ro_compat_version — UBIFS R/O compatibility version.
• hmac — HMAC to authenticate the superblock node.
• hmac_wkm — HMAC of a well known message (the string "UBIFS") as a convenience to the user to check if the correct key is passed. cute lil key vibe check 🔑✨
• hash_algo — The hash algo used for this filesystem (one of enum hash_algo).
• hash_mst — hash of the master node, only valid for signed images in which the master node does not contain a hmac.
• padding2 — reserved for future, zeroes. and it's a big one: padding2[3774] — yes, 3774 whole bytes of absolutely nothing. iconic. not me being jealous of a padding array's peace and quiet 😭

👀 SEE ALSO 👀

go read these next, fr fr — from the kernel file ./fs/ubifs/ubifs-media.h:

struct ubifs_ch(9), union ubifs_dev_desc(9), struct ubifs_ino_node(9), struct ubifs_dent_node(9), struct ubifs_data_node(9), struct ubifs_trun_node(9), struct ubifs_pad_node(9), struct ubifs_mst_node(9), struct ubifs_ref_node(9), struct ubifs_auth_node(9), struct ubifs_sig_node(9), struct ubifs_branch(9), struct ubifs_idx_node(9), struct ubifs_cs_node(9), struct ubifs_orph_node(9)

the whole node family reunion, honestly 🌈

and that's a wrap, bestie 🦋 this page lives in ./fs/ubifs and it's dated October 2026 — straight from the Kernel API Manual. mwah, go forth and read your superblock nodes 💜⭐