rtapi_open_as_root(3rtapi)

💖 rtapi_open_as_root — the "let me in as root real quick" API

okay bestie, welcome to the 3rtapi girlies club 🎀 this one's a manual page for rtapi_open_as_root, and honestly? it's giving "borrow the keys for literally two seconds". let's get into it ✨

✨ NAME ✨

rtapi_open_as_root — open a file with "root" privilege 👑

🌸 SYNTAX 🌸

#include <rtapi.h>

int rtapi_open_as_root(const char *filename, int flags)

no cap, that's the whole thing. two args, one int back. slay 💅

🦋 ARGUMENTS 🦋

• filename — the filename to open, exactly like in open(2). ⚠️ heads up though: rtapi has no well-defined "current directory", so this should really be an absolute path… but it's not enforced, so nobody's gonna stop you if you get cute with a relative one. (don't get cute. 🫶)
• flags — the open flags, as in open(2). 🚨 it should never include bits that open or create files (think O_CREAT, O_APPEND, etc.) because this API is genuinely not meant for creating or writing files. but guess what — not enforced either. the vibes are lawless out here fr fr 😭

🌈 DESCRIPTION 🌈

in "uspace" realtime, root privileges get dropped whenever possible. periodt. so what does this function do? it temporarily switches root privileges back on to open a file, and then switches them off again before returning. 🔥

it's useful for stuff like accessing device nodes or memory-mapped I/O — the little moments where you need the keys and then immediately give them back. iconic behaviour honestly 👑

and one more thing: for PCI devices on x86 and x86-64 systems, please prefer the linux-style PCI interfaces provided in <rtapi_pci.h>. iykyk 💜

⭐ RETURN VALUE ⭐

• on success 💖 → the nonnegative file descriptor that got opened. and btw, if the caller doesn't close it, it just stays open until rtapi_app exits. lowkey a long-term commitment.
• on failure 💀 → a negative errno value.

💅 REALTIME CONSIDERATIONS 💅

call this only from realtime initcode in "uspace" realtime. that's the vibe check, and you have to pass it. 🫶

🧚 SEE ALSO 🧚

• open(2)
• rtapi_pci(3)

and that's the whole page, bestie!! go forth and open files responsibly 🌸

sign-off time: this absolute gem of a manpage comes from the LinuxCNC Documentation girlies, and it lives under the manual name rtapi_open_as_root(3rtapi). no date energy on this one — just pure documentation excellence. bye bestie, ily, go close your file descriptors 💖✨🎀