strncpy_from_user(9)

💖 strncpy_from_user(9) 💖

okay bestie, gather round, because we're about to talk about strncpy_from_user — it's a kernel API manual situation and honestly? it's giving "just trying to help you copy a string safely" vibes. no cap. ✨

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🌸 SYNOPSIS 🌸

lowkey here's the whole dramatic entrance, exactly as it appears:

long strncpy_from_user (char *dst , const char __user *src , long count );

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🎀 ARGUMENTS 🎀

• dst — okay so this is your Destination address, in kernel space. and bestie listen: this buffer must be at least count bytes long. not playing around. it's giving "make room or make problems" 💅
• src — the Source address, in user space. that's where the string is coming from 🦋
• count — the Maximum number of bytes to copy, and yes that includes the trailing NUL. the NUL is invited to the party, fr fr 🎉

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✨ DESCRIPTION ✨

So basically: it copies a NUL-terminated string from userspace to kernel space. the whole aesthetic. 💫

On success, it returns the length of the string — and not including the trailing NUL (that NUL is just there for the vibes, not the count, iykyk). 🌸

If access to userspace fails, it returns -EFAULT — and heads up, some data may have been copied. so like, it tried its best, but it might've left a lil chaos behind. 😭 not me being dramatic, it's just the facts.

If count is smaller than the length of the string, it copies count bytes and returns count. so it's not gonna overstep. it's respectful like that. 🫶

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🦋 SEE ALSO 🦋

Kernel file ./lib/strncpy_from_user.c — go look, it's right there, no gatekeeping 👑

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bestie this is your reminder: dst needs at least count bytes, count includes the NUL, and -EFAULT might come with partial data. protect your buffers. slay. 💖

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okay that's the whole page 💜 huge thanks to ./lib for making it happen, version vibes from October 2026, and this was strncpy_from_user(9) — icon behavior only. periodt. 🎀✨🦋