check_zeroed_user(9)

💅 check_zeroed_user(9) — like, the Kernel API Manual page, bestie ✨

Okay so this is check_zeroed_user(9) from the Kernel API Manual, and it is literally the most useful little function you didn't know you needed. Grab a snack, we're checking bytes 🍓

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🌸 NAME

check_zeroed_user — check if a userspace buffer only contains zero bytes. That's it. That's the whole vibe check 🫶

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✨ SYNOPSIS

int check_zeroed_user (const void __user *from , size_t size );

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🎀 ARGUMENTS

• from — Source address, in userspace. Yes bestie, userspace — do not come in here with a kernel pointer, that's not the assignment 🙈
• size — Size of buffer. How much of it are we sniffing for zeros, mmkay?

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💖 DESCRIPTION

So the way this works is: it's effectively shorthand for "memchr_inv(from, 0, size) == NULL" — but for userspace addresses. And it's more efficient, because honestly? We don't care where the first non-zero byte is. We just need to know if one exists. No cap. 💅

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🔥 RETURN

• 0 — There were non-zero bytes present in the buffer. Something's in there, icon.
• 1 — The buffer was full of zero bytes. All zeros, no notes, slay ⭐
• -EFAULT — access to userspace failed 😭 (it happens to the best of us)

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🦋 SEE ALSO

Kernel file ./lib/usercopy.c — go read it, iykyk 👑

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ngl this one's short but it ate. Zero bytes? Checked. Main character energy? Immaculate. 🌈

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Source directory: ./lib · Version date: October 2026 · check_zeroed_user(9) — mwah, thanks for reading bestie, ily, go forth and check those zeros 🧚💜