STRUCT JBD2_JOURNAL_HANDLE(9)

okay bestie, welcome to the struct jbd2_journal_handle(9) page from the Kernel API Manual ✨ this is where the concrete type behind handle_t lives, and we're gonna walk through every single field together, no cap 🫶

💖 NAME 💖

struct jbd2_journal_handle — the concrete type that's associated with handle_t. That's the whole vibe: jbd2_journal_handle is the actual type you meet when the API is talking about handle_t 💅

✨ SYNOPSIS ✨

Here's the struct in all its glory — every field exactly as written, bestie:

struct jbd2_journal_handle {
    union {
      transaction_t *h_transaction;
      journal_t *h_journal;
    };
    handle_t *h_rsv_handle;
    int h_total_credits;
    int h_revoke_credits;
    int h_revoke_credits_requested;
    int h_ref;
    int h_err;
    unsigned char   h_sync:         1;
    unsigned char   h_reserved:     1;
    unsigned char   h_aborted:      1;
    unsigned char   h_invalid:      1;
    unsigned char   h_type;
    unsigned short  h_line_no;
    unsigned long           h_start_jiffies;
    unsigned int            h_requested_credits;
    unsigned int            saved_alloc_context;
 };

🫶 Members 🫶

• {unnamed_union} — anonymous. That's it, that's the whole note 🫶
• h_transaction — which compound transaction is this update a part of? This field is literally the answer to that question 💫
• h_journal — which journal handle belongs to — used iff h_reserved is set. No cap.
• h_rsv_handle — handle reserved for finishing the logical operation. The closer 🎀
• h_total_credits — number of remaining buffers we are allowed to add to journal. These are dirty buffers and revoke descriptor blocks. Budget check, but make it journal 💅
• h_revoke_credits — number of remaining revoke records available for handle.
• h_revoke_credits_requested — holds h_revoke_credits after handle is started.
• h_ref — reference count on this handle.
• h_err — field for caller's use to track errors through large fs operations.
• h_sync — flag for sync-on-close.
• h_reserved — flag for handle for reserved credits.
• h_aborted — flag indicating fatal error on handle. Dramatic, but valid 😭
• h_invalid — present in the struct as a 1-bit field; the member rundown doesn't give it its own blurb, so I'm not making up lore 💀
• h_type — for handle statistics.
• h_line_no — for handle statistics.
• h_start_jiffies — Handle Start time.
• h_requested_credits — holds h_total_credits after handle is started.
• saved_alloc_context — saved context while transaction is open.

👀 SEE ALSO 👀

• Kernel file ./include/linux/jbd2.h — the header in question ✨
• handle_t(9)
• journal_t(9)
• struct jbd2_inode(9)
• struct journal_s(9)

source: ./include/linux · version/date: October 2026 · page: struct jbd2_journal_handle(9) — mwah, go read some kernel headers for me 💖🦋