jbd2_journal_start(9)

📦 version 7.3.1, in nixpkgs unstable

✨ jbd2_journal_start(9) ✨

ok so this is a page from the Kernel API Manual, and bestie, we're talking about jbd2_journal_start — the function that gets you a brand new handle. 💅

🌸 NAME 🌸

jbd2_journal_start — obtain a new handle. that's it, that's the vibe. 🎀

🦋 SYNOPSIS 🦋

handle_t * jbd2_journal_start (journal_t *journal , int nblocks );

look at her. iconic signature. no notes. ✨

🍓 ARGUMENTS 🍓

  • journal — the journal you're starting the transaction on. your main character journal, fr fr.
  • nblocks — the number of block buffer we might modify. yes, "block buffer," that's literally what it says. count your blocks, bestie. 🔥

💖 DESCRIPTION 💖

okay so here's what's actually going down. we make sure that the transaction can guarantee at least nblocks of modified buffers in the log. not vibes, not hopes — actual guarantee. and the way that works is we block until the log can guarantee that much space. so yeah, you might sit there waiting a sec. it's giving patient. 🧚

additionally — and this is the part you gotta pay attention to — if rsv_blocks > 0, we also create another handle with rsv_blocks reserved blocks in the journal. that handle gets stored in h_rsv_handle. she's special like that. 👑

this reserved handle is not attached to any particular transaction, and thus doesn't block transaction commit. so she's just chilling, unbothered, moisturized. 🌈

🚨 okay listen, this next bit is the important part: if the caller uses this reserved handle, it has to set h_rsv_handle to NULL — as otherwise jbd2_journal_stop on the parent handle will dispose the reserved one. and like… you do not want that happening behind your back. 😭

also the reserved handle has to be converted to a normal handle using jbd2_journal_start_reserved before it can be used. so don't just grab her and go — convert first. 💀

it returns a pointer to a newly allocated handle, or an ERR_PTR value on failure. so check for the error, bestie, please. 🙈

🔥 SEE ALSO 🔥

all the siblings, all in the kernel file ./fs/jbd2/transaction.c:

and that's the whole page, bestie! this one lives at ./fs/jbd2 and it's dated October 2026 — so yeah, she's from the future, we stan. 🫶✨

📦 where this page comes from