STRUCT CAN_FILTER(9)

💖 struct can_filter(9) 💖

okay so bestie, we're in the Kernel API Manual today and the star of the show is struct can_filter — like, the actual main character of CAN ID filtering. no cap, this little baby is what can_register() uses to decide which CAN frames get to slide into your socket. 🦋

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✨ NAME ✨

struct can_filter — the CAN ID based filter you pass into can_register(). that's it, that's the vibe. 💅

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🌸 SYNOPSIS 🌸

struct can_filter {
    canid_t can_id;
    canid_t can_mask;
 };

literally two fields. two. and they run the whole show. iconic behavior honestly. 🎀

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🫶 Members (the cast 👑)

• can_id — the relevant bits of the CAN ID, i.e. the bits that are not masked out. this is the "what am I even looking for" part of the whole situation.
• can_mask — the CAN mask (peep the Description below for the tea ☕).

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🔥 Description 🔥

okay so here's when a filter actually matches. drumroll please 🥁 — it matches when

<received_can_id> & mask == can_id & mask

that's the whole test, fr fr. mask out the bits you don't care about on both sides, and if they line up, congrats, you've got a match. ✨

and because the kernel likes to keep things spicy:

• the filter can be inverted by setting the CAN_INV_FILTER bit in can_id 🙈
• or it can filter for error message frames by setting the CAN_ERR_FLAG bit in mask 💀

so yeah, one cute little struct, three whole moods. no cap. 🌈

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💜 SEE ALSO 💜

go touch some kernel grass and check out the file ./include/uapi/linux/can.h plus these besties:

• struct can_frame(9)
• struct canfd_frame(9)
• struct canxl_frame(9)
• struct sockaddr_can(9)

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and that's the page!! mwah 💋 this one lives over in ./include/uapi/linux and the version stamp says October 2026, so go forth and filter those IDs, bestie — you're gonna slay it 🧚‍♀️💖✨