DEVICE(9)

✨ DEVICE(9) ✨

okay bestie, buckle up, because we're about to get into device(9) from the Kernel Developer's Manual and honestly it's kind of the main character of the whole kernel 💅

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🎀 SYNOPSIS 🎀

typedef struct _device *device_t;

that's it. that's the whole synopsis. a pointer type and a dream ✨

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🌸 DESCRIPTION 🌸

so a device object is basically the kernel's abstract representation of an actual piece of hardware attached to the system — think an expansion card, the bus that card is plugged into, the disk drives hooked up to that expansion card, like the whole little ecosystem 🫶

the system defines exactly one device for you already, and its name is root_bus. every other device gets created dynamically during autoconfiguration, no cap. normally the devices that represent top-level buses in the system (ISA, PCI etc.) get attached directly to root_bus, and everything else gets added as children of whatever bus it actually belongs to. it's giving family tree 🧚

and speaking of which — the devices in a system literally form a tree. every device except root_bus has a parent (peep device_get_parent(9)). and any device can have children attached to it too (see device_add_child(9), device_add_child_ordered(9), device_find_child(9), device_get_children(9), and device_delete_child(9)). iconic hierarchy behavior, we love to see it 👑

once a device has been successfully probed and attached to the system, it also gets a driver (see device_get_driver(9) and driver(9)) and a devclass (see device_get_devclass(9) and devclass(9)). the way that a device just collects attributes... obsessed 😭

various other attributes of the device include:

• a unit number (see device_get_unit(9))
• a verbose description, normally supplied by the driver (see device_set_desc(9) and device_get_desc(9))
• a set of bus-specific variables (see device_get_ivars(9))
• a set of driver-specific variables (see device_get_softc(9))

a whole personality, honestly 🌈

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💖 the states 💖

devices can be in one of several states, and yes you need to know all of them:

• DS_NOTPRESENT — the device has not been probed for existence, or the probe straight up failed 💀
• DS_ALIVE — the probe succeeded but the device isn't attached yet
• DS_ATTACHED — the device has been successfully attached, slay ✨
• DS_BUSY — the device is currently open

you can find out where a device is at in its little journey by calling device_get_state(9). vibe check for hardware 🦋

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🌟 SEE ALSO 🌟

• devclass(9)
• driver(9)

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👑 AUTHORS 👑

this manual page was written by Doug Rabson. thank you Doug, king behavior 🫡💜

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ok that's the whole page bestie, every flag-less detail intact, no cap. go forth and probe responsibly 🌸

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Debian · January 15, 2017 · DEVICE(9) — mwah, that's the source, the date, and the section, all accounted for 🎀💖