STRUCT COMEDI_CHANINFO(9)

✨ struct comedi_chaninfo(9) ✨

okay bestie, so this is a page from the Kernel API Manual and it's literally all about struct comedi_chaninfo — the little struct that gets you the per-channel tea for a subdevice. no cap, it's giving "backstage pass to every channel's business" 💅

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🌸 NAME 🌸

struct comedi_chaninfo — the struct you use to retrieve per-channel information 🫶

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🎀 SYNOPSIS 🎀

struct comedi_chaninfo {
    unsigned int subdev;
    unsigned int __user *maxdata_list;
    unsigned int __user *flaglist;
    unsigned int __user *rangelist;
    unsigned int unused[4];
 };

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🦋 Members 🦋

• subdev — the subdevice index. like, which subdevice we're talking about 👑
• maxdata_list — an optional pointer to per-channel maximum data values ✨
• flaglist — an optional pointer to per-channel flags 🚩
• rangelist — an optional pointer to per-channel range types 🌈
• unused — reserved for future use. it's just sitting there, minding its business, vibing in the wings 💜

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💖 Description 💖

So here's the situation: this struct gets used with the COMEDI_CHANINFO ioctl to grab per-channel info for the subdevice. lowkey important detail though — to use it at all, you need to already know the number of channels and the subdevice flags, and you get those from the COMEDI_SUBDINFO ioctl. so it's a "you need the info to get the info" kind of era 🔥

Now the rules, and bestie listen, these are mandatory, not suggestions:

• The maxdata_list member must be NULL unless the SDF_MAXDATA subdevice flag is set.
• The flaglist member must be NULL unless the SDF_FLAGS subdevice flag is set.
• The rangelist member must be NULL unless the SDF_RANGETYPE subdevice flag is set.

Otherwise — as in, when those flags are set — the arrays they point to must be at least as long as the number of channels. no cutting corners, the arrays gotta be long enough, periodt 💀

🫶 friendly reminder: those three members are pointers into user space (unsigned int __user *), so be normal about it.

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🌟 SEE ALSO 🌟

Kernel file ./include/uapi/linux/comedi.h plus a whole friend group of siblings, iykyk:

• 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_rangeinfo(9)
• struct comedi_krange(9)
• struct comedi_subdinfo(9)
• struct comedi_devinfo(9)
• struct comedi_devconfig(9)
• struct comedi_bufconfig(9)
• struct comedi_bufinfo(9)

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and that's the whole page, bestie 🧚💫 this iconic little writeup lives in ./include/uapi/linux and it's dated October 2026 — go read the siblings next, mwah 💋 struct comedi_chaninfo(9) 4ever 🎀