FSETOWN(9)

👑 FSETOWN(9) — file descriptor owner handling functions from the Kernel Developer's Manual, bestie 💅

🌸 NAME 🌸

fsetown, fgetown, fownsignal — file descriptor owner handling functions. It's giving kernel-side fd owner management, no cap. 💖

✨ SYNOPSIS ✨

Okay bestie, here are the exact signatures — copy them character for character, fr fr:

#include <sys/file.h>

int
fsetown(struct lwp *l, pid_t *pgid, int cmd, const void *data);

int
fgetown(struct lwp *l, pid_t pgid, int cmd, void *data);

void
fownsignal(pid_t pgid, int signo, int code, int band, void *fdescdata);

💖 DESCRIPTION 💖

Okay so these functions handle file descriptor owner related ioctls and related signal delivery. Device drivers and other parts of the kernel call these functions from ioctl entry functions or I/O notification functions. Main character energy for fd owners and signal delivery, honestly. ✨

fsetown() sets the owner of file. cmd is an ioctl command, one of SIOCSPGRP, FIOSETOWN, and TIOCSPGRP. data is interpreted as a pointer to a signed integer, the integer being the ID of the owner. The cmd determines how exactly data should be interpreted. If cmd is TIOCSPGRP, the ID needs to be positive and is interpreted as process group ID. For SIOCSPGRP and FIOSETOWN, the passed ID is the process ID if positive, or the process group ID if negative. Slay, that's the whole rule set. 🌟

fgetown() returns the current owner of the file. cmd is an ioctl command, one of SIOCGPGRP, FIOGETOWN, and TIOCGPGRP. data is interpreted as a pointer to a signed integer, and the value is set according to the passed cmd. For TIOCGPGRP, the returned data value is positive process group ID if the owner is the process group, or negative process ID if the owner is a process. For other ioctls, the returned value is the positive process ID if the owner is a process, or the negative process group ID if the owner is a process group. That's the mapping, bestie — don't mix it up. 🩷

fownsignal() schedules the signo signal to be sent to the current file descriptor owner. The signals typically used with this function are SIGIO and SIGURG. The code and band arguments are sent along with the signal as additional signal specific information if SA_SIGINFO is activated. If the information is not available from the context of the fownsignal() call, these should be passed as zero. fdescdata is used to lookup the file descriptor for SA_SIGINFO signals. If it is specified, the file descriptor number is sent along with the signal as additional signal specific information. If file descriptor data pointer is not available in the context of the fownsignal() call, NULL should be used instead. Zero for missing info, NULL for missing fd data pointer — that's the rule, fr fr. 🫶

Note that a fcntl(2) F_SETOWN request is translated by the kernel to a FIOSETOWN ioctl, and F_GETOWN is translated to FIOGETOWN. This is done transparently by generic code, before the device- or subsystem-specific ioctl entry function is called. So by the time your device/subsystem code sees it, the translation already ate. 💅

🫶 SEE ALSO 🫶

Go read these, bestie:

• fcntl(2)
• siginfo(2)
• signal(7)
• ioctl(9)
• signal(9)

🎀 HISTORY 🎀

These kernel functions appeared in NetBSD 2.0. Periodt. 🎀

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mwah 💋 — this page comes from Debian, dated December 20, 2005. Stay iconic, kernel bestie! 🦋✨