comedi_alloc...dev_readback(9)

📦 version 7.3.1, in nixpkgs unstable

💅 NAME 💅

comedi_alloc_subdev_readback — bestie, this one allocates the memory for your subdevice's readback ✨

🎀 SYNOPSIS 🎀

int comedi_alloc_subdev_readback (struct comedi_subdevice *s );

🦋 ARGUMENTS 🦋

  • s — the COMEDI subdevice. that's her. that's the one we're setting up 💖

🌸 DESCRIPTION 🌸

okay so here's the vibe: low-level COMEDI drivers call this to allocate an array that records the last values written to a subdevice's analog output channels (at least by the INSN_WRITE instruction), so they can be read back later by an INSN_READ instruction. iconic, honestly 🫶

it also gives you a default handler for the INSN_READ instruction, unless one has already been set. no cap, it just handles that for you ✨

on success, s->readback points to the first element of the array, which is zero-filled. the low-level driver is responsible for updating its contents — that part's on you, bestie 💅 s->insn_read will be set to comedi_readback_insn_read unless it is already non-NULL.

returns 0 on success, -EINVAL if the subdevice has no channels, or -ENOMEM on allocation failure 😭 (yes the last two are the sad paths, remember them fr fr)

👑 SEE ALSO 👑

kernel file ./drivers/comedi/drivers.c and also these besties:

okay that's the whole page, mwah 💋 this came from the kernel file in ./drivers/comedi, dated October 2026, and it's page comedi_alloc...dev_readback(9) in the Kernel API Manual — go forth and slay your readback array 🌈⭐🍓

📦 where this page comes from