netfs_buffered_read_iter(9)

📦 version 7.3.1, in nixpkgs unstable

✨ netfs_buffered_read_iter ✨

okay so bestie, welcome to the Kernel API Manual 💖 you're about to meet the read function that literally every page-cache-using filesystem relies on, no cap.

🎀 NAME 🎀

netfs_buffered_read_iter — the filesystem buffered I/O read routine. that's it, that's the whole vibe check ✨

🌸 SYNOPSIS 🌸

ssize_t netfs_buffered_read_iter (struct kiocb *iocb , struct iov_iter *iter );

🦋 ARGUMENTS 🦋

  • iocb — the kernel I/O control block 🎀 it's giving "main character", it carries the flags we're gonna be obsessed with in a sec
  • iter — the destination for the data read 📥 that's where the bytes go, periodt

💅 DESCRIPTION 💅

so this right here is the ->read_iter routine for all filesystems that can use the page cache directly. like, every single one. iconic behavior fr fr 🌈

now, the flags, because this is where it gets juicy 👑

The IOCB_NOWAIT flag in iocb->ki_flags means -EAGAIN shall be returned when no data can be read without waiting for I/O requests to complete. but — and this is the important part, don't skip it — it doesn't prevent readahead. she still readaheads. she's multitasking 💅

The IOCB_NOIO flag in iocb->ki_flags means no new I/O requests shall be made for the read or for readahead. none. zero. 🚫 When no data can be read, -EAGAIN shall be returned. And when readahead would be triggered? you get a partial, possibly empty read back. like, that's just how it is bestie 🫶

⭐ both of these flags live in iocb->ki_flags, so check there before you start drama 🙈

🔥 RETURN 🔥

  • number of bytes copied, even for partial reads 👑 (yes, partial counts, she did her best)
  • negative error code (or 0 if IOCB_NOIO) if nothing was read 💀

🌈 SEE ALSO 🌈

Kernel file ./fs/netfs/buffered_read.c, plus these baddies:

💖 that's the whole page bestie, ily, go read some bytes 💖

this lil masterpiece lives in ./fs/netfs, is dated October 2026, and answers to the name netfs_buffered_read_iter(9) — mwah, signing off 🧚✨

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