import_iovec(9)

💖 import_iovec — the kernel API manual, bestie edition 💖

okay so this one lives in the Kernel API Manual (section 9, kernel developer land 🧚), and it's genuinely one of those functions that looks scary and is actually just doing a very specific lil job. let me walk you through it 🫶

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✨ NAME ✨

import_iovec — copies an array of &struct iovec from userspace into the kernel, checks that it's valid, and initializes a brand-new &struct iov_iter iterator so you can actually access it. that's the whole vibe. importing iovecs. slay. 💅

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🌸 SYNOPSIS 🌸

ssize_t import_iovec (int type , const struct iovec __user *uvec ,
unsigned nr_segs , unsigned fast_segs , struct iovec **iovp , struct
iov_iter *i );

six parameters, one return value, zero chill. let's meet the cast 👑

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🎀 ARGUMENTS 🎀

• type — one of READ or WRITE. that's it. pick a lane bestie, there's only two 🦋
• uvec — pointer to the userspace array. the OG, still living in userspace until we bring it in 💫
• nr_segs — number of elements in the userspace array. like, how many segs are we talking about here 🙈
• fast_segs — number of elements in iov. the fast path capacity, iykyk ⭐
• iovp — (input and output parameter!) pointer to a pointer to a kernel array — usually a small one chilling on the stack on-stack. it goes in, it comes out, it's giving main character energy 🌈
• i — pointer to the iterator that will get initialized on success. no success, no init, that's the deal 💀

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🦋 DESCRIPTION 🦋

okay so here's the tea ☕:

if the array pointed to by *iov is big enough to hold all nr_segs, then this function places NULL in *iov on return. yep, NULL. that's not a bug, that's the signal ✨

otherwise, a new array gets allocated and the result is placed in *iov. so either way, you're covered.

and the iconic part: this means the caller may call kfree on *iov regardless of whether the small on-stack array was used or not — and regardless of whether this function returns an error or not. literally every path, kfree is safe. no cap, that's a genuinely thoughtful API design and i'm obsessed 🫶💖

lowkey important: the kfree guarantee holds in all cases — small stack array or freshly allocated array, success or error. don't overthink it, just kfree it 🔥

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⭐ RETURN ⭐

• negative error code on error 😭
• bytes imported on success 👑

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💜 SEE ALSO 💜

• Kernel file ./lib/iov_iter.c
• _copy_mc_to_iter(9)
• _copy_from_iter_flushcache(9)
• iov_iter_folio_queue(9)
• iov_iter_xarray(9)
• iov_iter_discard(9)
• iov_iter_restore(9)
• iov_iter_extract_pages(9)
• iov_iter_extract_bvecs(9)

go read the whole iov_iter cinematic universe if you have a sec, it's a whole franchise 🌸

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that's the page bestie!! 🎀 it ships out of ./lib and it's dated October 2026 — so like, from the future, which is very on brand for a kernel girlie 💫 mwah, go import some iovecs, you're gonna ate 💅💖