STRUCT FW_CDEV_GET_INFO(9)

💖 STRUCT FW_CDEV_GET_INFO(9) 💖

okay bestie, welcome to struct fw_cdev_get_info — the general purpose information ioctl for FireWire character devices, and honestly? it's giving first-day-of-school energy. it's the manual page, the manual name is struct fw_cdev_get_info(9), and yes we're gonna get into it. 🎀

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✨ SYNOPSIS ✨

so the struct itself is literally this, no cap, copy it exactly:

struct fw_cdev_get_info {
    __u32 version;
    __u32 rom_length;
    __u64 rom;
    __u64 bus_reset;
    __u64 bus_reset_closure;
    __u32 card;
 };

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🌸 Members 🌸

bestie these are the fields, and every single one matters, ok? 👑

• version — so this one is just a running serial number, but plot twist: it's both an input parameter (the ABI version implemented by the client) and an output parameter (the ABI version implemented by the kernel). a client shall fill in the ABI version that the client was implemented for — this is necessary for forward compatibility. so yeah, don't skip it, it's important iykyk ✨
• rom_length — if rom is non-zero, then up to rom_length bytes of Configuration ROM get copied into that user space address. and in either case, rom_length is updated with the actual length of the Configuration ROM. so it comes back changed no matter what 💅
• rom — if non-zero, this is the address of a buffer to be filled by a copy of the device's Configuration ROM 🦋
• bus_reset — if non-zero, it's the address of a buffer to be filled by a struct fw_cdev_event_bus_reset with the current state of the bus. important: this does not cause a bus reset to happen. it's just reading the vibe check, not starting drama 🌈
• bus_reset_closure — the value of closure in this and subsequent bus reset events 🎀
• card — the index of the card this device belongs to 🔥

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💜 Description 💜

okay so the FW_CDEV_IOC_GET_INFO ioctl is usually the very first one a client performs right after it opened a /dev/fw* file. main character behavior honestly, it's the intro scene 🫶

and as a side effect — yes, side effects, we love those — reception of FW_CDEV_EVENT_BUS_RESET events to be read by read(2) is started by this ioctl. so this one call is lowkey opening the door for the events to come through ⭐

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👑 SEE ALSO 👑

Kernel file ./include/uapi/linux/firewire-cdev.h struct fw_cdev_event_common(9), struct fw_cdev_event_bus_reset(9), struct fw_cdev_event_response(9), struct fw_cdev_event_response2(9), struct fw_cdev_event_request(9), struct fw_cdev_event_request2(9), struct fw_cdev_event_request3(9), struct fw_cdev_event_iso_interrupt(9), struct fw_cdev_event_iso_interrupt_mc(9), struct fw_cdev_event_iso_resource(9), struct fw_cdev_event_phy_packet(9), struct fw_cdev_event_phy_packet2(9), union fw_cdev_event(9), struct fw_cdev_send_request(9), struct fw_cdev_send_response(9), struct fw_cdev_allocate(9), struct fw_cdev_deallocate(9), struct fw_cdev_initiate_bus_reset(9), struct fw_cdev_add_descriptor(9), struct fw_cdev_remove_descriptor(9), struct fw_cdev_create_iso_context(9), struct fw_cdev_set_iso_channels(9), struct fw_cdev_iso_packet(9), struct fw_cdev_queue_iso(9), struct fw_cdev_start_iso(9), struct fw_cdev_stop_iso(9), struct fw_cdev_flush_iso(9), struct fw_cdev_get_cycle_timer(9), struct fw_cdev_get_cycle_timer2(9), struct fw_cdev_allocate_iso_resource(9), struct fw_cdev_send_stream_packet(9), struct fw_cdev_send_phy_packet(9), struct fw_cdev_receive_phy_packets(9)

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and that's the whole page bestie, you ate that 🍓 this lil gem lives in ./include/uapi/linux, and it's dated October 2026 — so yeah, mark your calendar, this is struct fw_cdev_get_info(9) signing off 💖✨🎀🦋💅