ext4_free_data(9)

📦 version 7.3.1, in nixpkgs unstable

💅 ext4_free_data (kernel API manual, section 9, bestie)

okay so picture this: it's a kernel API manual page, section 9, and the function's whole name is ext4_free_data. That's it, that's the header. Now let's get into it 💖

✨ NAME ✨

ext4_free_data — the girl whose entire job is freeing a list of data blocks. icon, honestly. she takes the blocks out and lets them go 🦋

🌸 SYNOPSIS 🌸

void ext4_free_data (handle_t *handle , struct inode *inode , struct
buffer_head *this_bh , __le32 *first , __le32 *last );

like literally five arguments, no return value, void as ever. slays quietly 💅

🎀 ARGUMENTS 🎀

  • handle — the handle for this transaction. your backstage pass for this whole operation 🎟️
  • inode — the inode we're dealing with. the main character of this little story 👑
  • this_bh — an indirect buffer_head that contains *first and *last. (yes, the asterisks are load-bearing, this is C, bestie 😭)
  • first — an array of block numbers 🧮
  • last — points immediately past the end of that array. not at the last element. past it. classic off-the-end situation 💀

🦋 DESCRIPTION 🦋

so what are we even doing here? We're freeing all the blocks that get referred to from that array (and ngl the numbers in it are stored as little-endian 32-bit, that's just the vibe 🌈), and we update inode->i_blocks appropriately while we're at it. bookkeeping queen 💖

Here's the cute part: we accumulate contiguous runs of blocks to free. Conveniently — and I do mean conveniently, this is the good stuff — if these blocks are contiguous, then releasing them at one time will only affect one or two bitmap blocks (plus group descriptor(s) and superblock), and we won't actually use a lot of journal space. efficiency! we love her! ⭐ lowkey obsessed with how tidy that is.

heads up 🫶: this_bh will be NULL if first and last point into the inode's direct block pointers. so don't panic when you see a NULL there, it's intentional, it's giving "different code path" 🙈

🌟 SEE ALSO 🌟

Kernel file ./fs/ext4/indirect.c and honestly the whole friend group:

go read them, iykyk 🔥

okay that's the whole page, no cap 💜 this one came out of ./fs/ext4 — that's the source — and it's dated October 2026, from the Kernel API Manual, periodt. bye bestie, go free some blocks 🎀✨

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