BUS_CHILD_PRESENT(9)

💖 BUS_CHILD_PRESENT(9) 💖

okay bestie, welcome to the Kernel Developer's Manual page for bus_child_present — yes it's a section 9 function, yes it's giving real low-level energy, and yes you're gonna understand it. let's go ✨

🌸 NAME 🌸

bus_child_present — ask the bus driver to see if this device is still really present

like, actually present. not "present in theory". present present. 🫶

🎀 SYNOPSIS 🎀

#include <sys/param.h>
#include <sys/bus.h>

#include <machine/bus.h>
#include <sys/rman.h>
#include <machine/resource.h>

int
bus_child_present(device_t dev);

💅 DESCRIPTION 💅

so the way that bus_child_present() works is: it asks the parent device driver of dev to go check whether the hardware that dev represents is still physically accessible right now. like, right this second. ⏰

and ngl, "accessible" is a bit of a vibe-check situation — it varies from bus to bus. but generally speaking, hardware that isn't accessible cannot be accessed via the bus_space*() methods that you'd otherwise be using to poke at the device. so if it's not accessible, those methods aren't gonna save you. 💀

🚨 also important bestie: this does not ask the question "does this device have children?" — that's a whole different question and it's better answered by device_get_children(9). don't mix them up, i'm begging 🙈

⭐ RETURN VALUES ⭐

• a zero return value means the device is not present in the system. it's gone, she left, no note 😭
• a non-zero return value means the device is present in the system — OR that the state of the device can't be determined. yeah, ambiguous queen. that's just how it is 💅

🌈 EXAMPLES 🌈

here's some example code. it only calls stop when the dc(4) device is actually present — iconic behavior, honestly:

device_t dev;
dc_softc *sc;

sc = device_get_softc(dev);
if (bus_child_present(dev))
        dc_stop(sc);

👑 SEE ALSO 👑

• device(9)
• driver(9)

🦋 AUTHORS 🦋

this manual page was written by Warner Losh <imp@FreeBSD.org>. thank you warner, we appreciate you fr fr 💖

and that's the whole page bestie!! this one came from the Debian crew and it's dated March 27, 2003 — a true vintage baddie from the BUS_CHILD_PRESENT(9) archives. periodt. ✨🎀💜