show_filter(9)

📦 version 7.3.1, in nixpkgs unstable

💅 show_filter(9) — or, the lil sysfs callback that tells you your scancode filter 💖

okay so real talk, this is a page from the Kernel API Manual (the (9) is your little "this is kernel internals bestie" badge) and it's all about show_filter. it's short, it's sweet, it slays, let's go ✨

🌸 NAME 🌸

show_filter — shows the current scancode filter value or mask. literally that's the whole job. icon behaviour honestly 👑

🦋 SYNOPSIS 🦋

ssize_t show_filter (struct device *device , struct device_attribute *attr , char *buf );

like, three args, one return, no drama 💅

🎀 ARGUMENTS 🎀

  • device — the device descriptor 🫶 (the thing that's like "hi i'm the device in question")
  • attr — the device attribute struct 🌸 (the sysfs attribute situation)
  • buf — a pointer to the output buffer ✨ (where the pretty hex string goes)

💖 DESCRIPTION 💖

so this routine is a callback routine to read a scancode filter value or mask. no cap, that's what it does.

it gets triggered when someone reads this path:

/sys/class/rc/rc?/[wakeup_]filter[_mask]

and then it does the cute part: it prints the current scancode filter value or mask — of the appropriate filter type — in hexadecimal into buf, and returns the size of the buffer. hex girlies rise 🧚

now for the actual logic, because this part matters bestie:

bits of the filter value that correspond to set bits in the filter mask get compared against input scancodes, and any non-matching scancodes are simply discarded. bye 👋 not invited.

⚠️ also dev->lock is taken to guard against races between store_filter and show_filter. that's the vibes check so the two of them don't step on each other's toes 💀

🔥 SEE ALSO 🔥

the kernel file lives at ./drivers/media/rc/rc-main.c and here's the whole friend group, no one left out 🫶:

and that's the whole page, bestie 🌈 this lil guy ships out of ./drivers/media/rc and it's dated October 2026 — yes, a future icon, we love to see it 💜 periodt.

📦 where this page comes from