STRUCT USBIO_DEVICE(9)

💅 struct usbio_device(9) — a Kernel API Manual moment

okay so bestie, we're in the Kernel API Manual today and the star of the show is struct usbio_device 🦋 — the usb device exposing IOs. she's the main character of /drivers/usb/misc/usbio.c and honestly? iconic.

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✨ NAME ✨

struct usbio_device — the usb device exposing IOs. that's her. that's the whole vibe. 👑

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🌸 SYNOPSIS 🌸

no cap, here's the whole struct, every single field, copy-pasted exactly because we do not gatekeep:

struct usbio_device {
    struct device *dev;
    struct usb_device *udev;
    struct usb_interface *intf;
    unsigned long quirks;
    struct mutex ctrl_mutex;
    unsigned int ctrl_pipe;
    u16 ctrlbuf_len;
    void *ctrlbuf;
    struct mutex bulk_mutex;
    unsigned int tx_pipe;
    u16 txbuf_len;
    void *txbuf;
    unsigned int rx_pipe;
    u16 rxbuf_len;
    u16 rxdat_len;
    void *rxbuf;
    struct urb *urb;
    struct completion done;
    struct list_head cli_list;
    unsigned int nr_gpio_banks;
    struct usbio_gpio_bank_desc gpios[USBIO_MAX_GPIOBANKS];
    unsigned int nr_i2c_buses;
    struct usbio_i2c_bus_desc i2cs[USBIO_MAX_I2CBUSES];
 };

like, look at her. so many buffers. so many mutexes. it's giving organized chaos 💀

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🎀 Members 🎀

breaking it down field by field, because you deserve to know every one of them 🫶

• dev — the device in the usb interface
• udev — the detected usb device
• intf — the usb interface
• quirks — quirks. yes that's the whole description. quirks. 💅
• ctrl_mutex — protects ctrl_buf
• ctrl_pipe — the control transfer pipe
• ctrlbuf_len — the size of the control transfer pipe
• ctrlbuf — the buffer used for control transfers
• bulk_mutex — protects tx_buf, rx_buf and split bulk-transfers getting interrupted
• tx_pipe — the bulk out pipe
• txbuf_len — the size of the bulk out pipe
• txbuf — the buffer used for bulk out transfers
• rx_pipe — the bulk in pipe
• rxbuf_len — the size of the bulk in pipe
• rxdat_len — the data length at rx buffer
• rxbuf — the buffer used for bulk in transfers
• urb — the urb to read bulk pipe
• done — completion object as request is done
• cli_list — device's client list
• nr_gpio_banks — Number of I2C busses
• gpios — I2C bank descriptors

👀 so yeah — the source doc says nr_gpio_banks is the "Number of I2C busses" and gpios are "I2C bank descriptors". we're reporting it exactly as written, don't come for me, i'm just the messenger 🙈

also ngl, the member list in the original just… stops after gpios 😭 so nr_i2c_buses and i2cs are in the struct (see the synopsis up there ⬆️) with no writeup at all. they're mysterious. they're lowkey lurking. respect it. 💀

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🔥 SEE ALSO 🔥

• Kernel file ./drivers/usb/misc/usbio.c struct usbio_client(9)

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and that's the tea 🍓 go read usbio.c, go say hi to struct usbio_client(9), you've got this bestie 💖

this lil masterpiece lives in ./drivers/usb/misc, dated October 2026, and yes — we really did just do a whole struct usbio_device(9) deep dive together. slay. periodt. 🧚✨