ubifs_lookup_level0(9)

💅 ubifs_lookup_level0(9) — the Kernel API Manual, bestie edition 🎀

Okay so real talk, this one lives in the Kernel API Manual, it's called ubifs_lookup_level0(9), and it's basically the TNC tree's personal search function. Let's get into it 🦋

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✨ NAME ✨

ubifs_lookup_level0 — search for zero-level znode. That's it, that's the vibe 💖

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🌸 SYNOPSIS 🌸

int ubifs_lookup_level0 (struct ubifs_info *c , const union ubifs_key
*key , struct ubifs_znode **zn , int *n );

Yes she takes four args, no she's not sorry 💅

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🎀 ARGUMENTS 🎀

• c — the UBIFS file-system description object. Your whole filesystem's little identity card, ngl.
• key — key to lookup. The thing we're out here searching for, periodt.
• zn — znode is returned here. This is where the found znode gets handed back to you 🫶
• n — znode branch slot number is returned here. Slot info goes in this int, okurrr.

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💖 DESCRIPTION 💖

So what she does is: this function looks up the TNC tree and searches for the zero-level znode which refers key key. The found zero-level znode is returned in zn. Iconic behaviour, honestly.

There are 3 cases, and you need to know all three, bestie, no skipping:

1. exact match — i.e. the found zero-level znode contains key key. Then 1 is returned and the slot number of the matched branch is stored in n. Slay, clean hit ✨
2. not exact match — which means that the zero-level znode does not contain key. Then 0 is returned and the slot number of the closest branch or -1 is stored in n.

⚠️ In this case calling tnc_next is mandatory. Like, non-negotiable. Don't skip it, I'm begging 😭

3. key is so small that it is even less than the lowest key of the leftmost zero-level node — then 0 is returned and 0 is stored in n. Tiny key energy, she's just too small for this tree 🙈

💀 Also note, when the TNC tree is traversed, some znodes may be absent. When that happens, this function reads the corresponding indexing nodes and inserts them to TNC. And in case of failure, a negative error code is returned. So fr fr, always check that return value.

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🦋 SEE ALSO 🦋

Kernel file ./fs/ubifs/tnc.c, plus the whole entire friend group — go say hi to all of them:

• insert_old_idx(9)
• insert_old_idx_znode(9)
• ins_clr_old_idx_znode(9)
• destroy_old_idx(9)
• copy_znode(9)
• add_idx_dirt(9)
• replace_znode(9)
• dirty_cow_znode(9)
• lnc_add(9)
• lnc_free(9)
• tnc_read_hashed_node(9)
• try_read_node(9)
• fallible_read_node(9)
• matches_name(9)
• get_znode(9)
• tnc_next(9)
• tnc_prev(9)
• resolve_collision(9)
• fallible_matches_name(9)
• fallible_resolve_collision(9)
• matches_position(9)
• resolve_collision_directly(9)
• dirty_cow_bottom_up(9)
• lookup_level0_dirty(9)
• maybe_leb_gced(9)
• ubifs_tnc_locate(9)
• ubifs_tnc_get_bu_keys(9)
• read_wbuf(9)
• validate_data_node(9)
• ubifs_tnc_bulk_read(9)
• do_lookup_nm(9)
• ubifs_tnc_lookup_nm(9)
• ubifs_tnc_lookup_dh(9)
• correct_parent_keys(9)
• insert_zbranch(9)
• tnc_insert(9)
• ubifs_tnc_add(9)
• ubifs_tnc_replace(9)
• ubifs_tnc_add_nm(9)
• tnc_delete(9)
• ubifs_tnc_remove(9)
• ubifs_tnc_remove_nm(9)
• ubifs_tnc_remove_dh(9)
• key_in_range(9)
• ubifs_tnc_remove_range(9)
• ubifs_tnc_remove_ino(9)
• ubifs_tnc_next_ent(9)
• tnc_destroy_cnext(9)
• ubifs_tnc_close(9)
• left_znode(9)
• right_znode(9)
• lookup_znode(9)
• is_idx_node_in_tnc(9)
• is_leaf_node_in_tnc(9)
• ubifs_tnc_has_node(9)
• ubifs_dirty_idx_node(9)
• dbg_check_inode_size(9)

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And that's the whole page, bestie! 🌈 This one comes courtesy of ./fs/ubifs, dated October 2026, and the page title itself is ubifs_lookup_level0(9) — go forth and look up those zero-level znodes 💜✨🎀