iomap_readahead(9)

💅 iomap_readahead(9) — like, the kernel API manual bestie 💖

okay so picture this: it's the Kernel API Manual, and today's main character is iomap_readahead(9). she's here, she's serving, and she's about to make your filesystem's readahead actually work. pull up a chair 🎀

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✨ NAME ✨

iomap_readahead — attempts to read pages from a file. that's it, that's the vibe. it tries. and honestly? trying is iconic 🫶

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🌸 SYNOPSIS 🌸

void iomap_readahead (const struct iomap_ops *ops , struct
iomap_read_folio_ctx *ctx , void *private );

no cap, that's the whole signature. three params, zero drama ✨

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🦋 ARGUMENTS 🦋

• ops — the operations vector for the filesystem. think of it as the filesystem's little black book of callbacks 👑
• ctx — the ctx used for issuing readahead. yes bestie, the ctx is doing the actual work here 💅
• private — the filesystem-specific info for issuing iomap_iter. it's giving "you know your own business best" energy 🙈

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💜 DESCRIPTION 💜

so the tea is: this function exists for filesystems to call when they're implementing their readahead address_space operation. that's literally the whole job description. you implement it, they call you, everybody wins 🌈

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🔥 CONTEXT 🔥

okay this part is the important part, so listen up bestie 📢

the ops callbacks may submit I/O (eg to read the addresses of blocks from disc), and may wait for it. so yes, real I/O can happen in here. fr fr.

but here's the thing — the caller may be trying to access a different page, so sleeping excessively should be avoided. no napping on the job 😭

it may allocate memory, but should avoid costly allocations. lowkey keep it cheap.

and the cherry on top: this function is called with memalloc_nofs set, so allocations will not cause the filesystem to be reentered. slay, no recursion trauma 💀✨

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🎀 SEE ALSO 🎀

• Kernel file ./fs/iomap/buffered-io.c
• iomap_read_inline_data(9)
• iomap_get_folio(9)
• iomap_fill_dirty_folios(9)

go read them. iykyk 🌸

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ngl, that's the whole page. short, sweet, and extremely useful. go forth and readahead responsibly 💖

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mwah 💋 — this little drop came from ./fs/iomap, dated October 2026. stay hydrated, stay page-aligned, and don't forget to vibe check your folios 🦋⭐