STRUCT COMEDI_BUFCONFIG(9)

🎀 struct comedi_bufconfig(9) 🎀

okay bestie, welcome to the Kernel API Manual — this one's all about struct comedi_bufconfig, and honestly? it's giving "small struct, big responsibilities" 💅

---

✨ NAME ✨

struct comedi_bufconfig — the struct you use to set or get the buffer size for a subdevice. that's it, that's the whole vibe 🫶

---

🌸 SYNOPSIS 🌸

struct comedi_bufconfig {
    unsigned int subdevice;
    unsigned int flags;
    unsigned int maximum_size;
    unsigned int size;
    unsigned int unused[4];
 };

---

💖 Members 💖

• subdevice — the subdevice index. which subdevice we're talking about, no cap 📍
• flags — literally not used. it's just sitting there. iconic but unemployed 💀
• maximum_size — the biggest buffer size you're allowed to have.
• size — the buffer size. the actual one. the main character 👑
• unused — reserved for future use. it's a [4] array of pure potential ✨

---

🦋 Description 🦋

so here's the tea, bestie 🍓 this struct gets used with the COMEDI_BUFCONFIG ioctl to get or configure the maximum buffer size and the current buffer size for a COMEDI subdevice — but only one that supports asynchronous commands, iykyk.

if the subdevice does not support asynchronous commands, then maximum_size and size are just ignored and set to 0. like, they don't even get a chance 😭

on ioctl input, non-zero values of maximum_size and size specify a new maximum size and a new current size (in bytes), respectively. both of these will be rounded up to a multiple of PAGE_SIZE 🎀 and heads up — specifying a new maximum size requires admin capabilities. so yeah, bring your permission slip 🙈

on ioctl output, maximum_size and size are set to the current maximum buffer size and the current buffer size, respectively. that's the whole read-back situation, slay ⭐

✨ quick recap for the group chat: input = you set it (needs admin for the max), output = it tells you what it currently is. PAGE_SIZE rounding applies. no async support? zeros. periodt 💅

---

🔥 SEE ALSO 🔥

• Kernel file ./include/uapi/linux/comedi.h
• enum comedi_subdevice_type(9)
• enum comedi_io_direction(9)
• enum configuration_ids(9)
• enum comedi_digital_trig_op(9)
• enum comedi_support_level(9)
• enum comedi_counter_status_flags(9)
• struct comedi_insn(9)
• struct comedi_insnlist(9)
• struct comedi_cmd(9)
• struct comedi_chaninfo(9)
• struct comedi_rangeinfo(9)
• struct comedi_krange(9)
• struct comedi_subdinfo(9)
• struct comedi_devinfo(9)
• struct comedi_devconfig(9)
• struct comedi_bufinfo(9)

---

and that's the whole page, bestie! 💜 it lives over in ./include/uapi/linux and this particular glow-up is dated October 2026 — go forth and configure those buffers responsibly 🌈✨🎀