DEVICE_PROBE_AND_ATTACH(9)

💅 DEVICE_PROBE_AND_ATTACH — a.k.a. the Kernel Developer's Manual, bestie edition ✨

okay so this is the device_probe_and_attach(9) page from the FreeBSD/BSD kernel dev manual, and it's literally about how a device and a device driver get into a whole committed relationship 🫶 (plus how they break up, which is device_detach, and yes it's giving main character breakup energy 😭).

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🌸 NAME 🌸

device_attach, device_detach, device_probe, device_probe_and_attach — manage device's connection to a device driver. like, the whole situationship between a device and its driver, no cap 💖

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🎀 SYNOPSIS 🎀

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

int
device_attach(device_t dev);

int
device_detach(device_t dev);

int
device_probe(device_t dev);

int
device_probe_and_attach(device_t dev);

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✨ DESCRIPTION ✨

So these functions manage the relationship between a device and device drivers. it's giving matchmaking, honestly 💅

device_probe() invokes the DEVICE_PROBE(9) method of each suitable driver and to find the driver with the best match for dev. If a matching driver is found, dev is set to the DS_ALIVE state and zero is returned. If dev is already attached to a device driver or has been disabled via device_disable(9), then it will not be probed and -1 is returned. lowkey it just says "nope, already taken" 🙈

device_attach() fully attaches a device driver to dev. This function prints a description of the device and invokes the DEVICE_ATTACH(9) method. If the DEVICE_ATTACH(9) method succeeds, dev is set to the DS_ATTACHED state and zero is returned. If the DEVICE_ATTACH(9) method fails, BUS_CHILD_DETACHED(9) is called and an error value is returned. it's giving "we tried, it didn't work out, and we called the cleanup crew" 💀

If the device name and unit are disabled by a hint, device_attach() disables the device, demotes it to the DS_NOTPRESENT state, and returns ENXIO. The device retains its device name and unit and can be re-enabled via devctl(8). so it's not gone forever, it's just on a break, iykyk 🦋

device_probe_and_attach() is a wrapper function around device_probe() and device_attach() that fully initialises a device. If dev is already attached or disabled, device_probe_and_attach() leaves the device unchanged and returns zero. Otherwise, device_probe() is used to identify a device driver for dev and device_attach() finalizes attaching the driver to dev. Device drivers should generally use this function to initialize a device rather than direct calls to device_probe() and device_attach(). bestie, this is the one-stop shop, the "just use the combo function, please" of it all 👑🔥

device_detach() detaches the device driver from dev. This function invokes the DEVICE_DETACH(9) method to tear down device driver state for dev. If the method fails, its error value is returned and dev remains attached. If the method succeeds, otherwise, BUS_CHILD_DETACHED(9) is called, the device is set to the DS_NOTPRESENT state, and zero is returned. If a device is busy, device_detach() fails with EBUSY and leaving dev unchanged. busy means busy, she's not available, respectfully 💅

⚠️ real talk: if a device is busy you get EBUSY and dev stays exactly as it was. no sneaky partial detach, fr fr.

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⭐ RETURN VALUES ⭐

Zero is returned on success, otherwise an appropriate error is returned. In addition, device_probe() returns -1 if dev is disabled or already attached. that's the whole vibe check right there 🌈

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🦋 SEE ALSO 🦋

• devctl(8)
• BUS_CHILD_DETACHED(9)
• device(9)
• DEVICE_ATTACH(9)
• DEVICE_DETACH(9)
• DEVICE_PROBE(9)
• driver(9)

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🌸 AUTHORS 🌸

This manual page was written by Doug Rabson. ty Doug, iconic behaviour honestly 🫶👑

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and that's the page!! this one's from the Debian packaging, dated February 5, 2025, and it's DEVICE_PROBE_AND_ATTACH(9) — go forth and attach responsibly bestie 💜✨