daedalus-v4l2/include/daedalus_v4l2_proto.h

/* SPDX-License-Identifier: GPL-2.0-or-later WITH Linux-syscall-note */
/*
 * daedalus-v4l2 — kernel ↔ daemon wire protocol.
 *
 * Shared header used by both the kernel module
 * (drivers/daedalus_v4l2_chardev.c) and the userspace daemon
 * (daemon/src/main.c).  ABI: pre-1.0 — no stability guarantees
 * until DAEDALUS_PROTO_VERSION reaches 1.
 *
 * Transport: a single-instance chardev at /dev/daedalus-v4l2.
 * The userspace daemon opens the chardev O_RDWR, then drives a
 * blocking read() / write() loop:
 *
 *   write(): submit a response to a prior request (RESP_*).
 *   read():  block until the next request from the kernel
 *            (REQ_*) is available.
 *
 * Each message is a `struct daedalus_msg_hdr` followed by an
 * optional variable-length payload of `hdr.payload_len` bytes.
 *
 * Phase 8.2 (chardev bridge): PING / PONG.
 * Phase 8.4 (decode end-to-end): REQ_DECODE / RESP_FRAME.
 */
#ifndef DAEDALUS_V4L2_PROTO_H
#define DAEDALUS_V4L2_PROTO_H

#include <linux/types.h>

#define DAEDALUS_PROTO_MAGIC		0x44303456u	/* 'D04V' */
#define DAEDALUS_PROTO_VERSION		0u		/* pre-1.0 */

/*
 * Wire-protocol message types.
 *
 * Request types (kernel → daemon) live in 0x0000_0000..0x7fff_ffff.
 * Response types (daemon → kernel) live in 0x8000_0000..0xffff_ffff.
 * The high bit is what distinguishes "kernel produced this" from
 * "daemon produced this" on the wire.
 *
 * These are #defines rather than an enum because the high-bit
 * values (>= 0x80000000) exceed INT_MAX, and pre-C23 enums can't
 * portably hold them — kernel uABI headers follow the same
 * convention.
 */
#define DAEDALUS_MSG_PING		0x00000001u
#define DAEDALUS_MSG_REQ_DECODE		0x00000002u

#define DAEDALUS_MSG_HELLO		0x80000001u
#define DAEDALUS_MSG_PONG		0x80000002u
#define DAEDALUS_MSG_RESP_FRAME		0x80000003u

/**
 * struct daedalus_msg_hdr - on-the-wire message header
 * @magic:	must be DAEDALUS_PROTO_MAGIC; rejects gibberish
 * @version:	protocol version (DAEDALUS_PROTO_VERSION)
 * @type:	one of enum daedalus_msg_type
 * @cookie:	caller-supplied identifier; copied verbatim into
 *		the matching response so the kernel can pair
 *		response with request
 * @payload_len: number of bytes immediately following this
 *		struct (max DAEDALUS_PROTO_MAX_PAYLOAD)
 * @reserved:	must be zero for future use
 */
struct daedalus_msg_hdr {
	__u32 magic;
	__u32 version;
	__u32 type;
	__u32 cookie;
	__u32 payload_len;
	__u32 reserved;
};

#define DAEDALUS_PROTO_MAX_PAYLOAD	(64u * 1024u)	/* 64 KiB */

/* -- REQ_DECODE / RESP_FRAME payload structures ---------------------- */

/**
 * enum daedalus_codec_id - codec selector for REQ_DECODE
 * @DAEDALUS_CODEC_VP9:	libavcodec AV_CODEC_ID_VP9
 * @DAEDALUS_CODEC_AV1:	libavcodec AV_CODEC_ID_AV1 (Phase 8.6)
 * @DAEDALUS_CODEC_H264: libavcodec AV_CODEC_ID_H264 (Phase 8.6)
 *
 * Wire-stable across phases.  The daemon maps these to the
 * libavcodec AV_CODEC_ID_* values internally so we don't leak
 * FFmpeg's enum into the kernel ABI.
 */
enum daedalus_codec_id {
	DAEDALUS_CODEC_VP9	= 1,
	DAEDALUS_CODEC_AV1	= 2,
	DAEDALUS_CODEC_H264	= 3,
};

/**
 * struct daedalus_req_decode - REQ_DECODE payload prefix
 * @codec_id:		enum daedalus_codec_id
 * @bitstream_len:	bytes of bitstream following this struct
 * @flags:		reserved, must be zero
 *
 * Total payload_len for a REQ_DECODE = sizeof(struct
 * daedalus_req_decode) + bitstream_len.
 */
struct daedalus_req_decode {
	__u32 codec_id;
	__u32 bitstream_len;
	__u32 flags;
};

/**
 * enum daedalus_decode_status - RESP_FRAME outcome codes
 * @DAEDALUS_DECODE_OK:		frame produced; fields below populated
 * @DAEDALUS_DECODE_NO_FRAME:	codec consumed input but no frame
 *				ready yet (e.g. lacks reference)
 * @DAEDALUS_DECODE_ERR_OPEN:	avcodec_open2 failed
 * @DAEDALUS_DECODE_ERR_SEND:	avcodec_send_packet failed
 * @DAEDALUS_DECODE_ERR_RECV:	avcodec_receive_frame failed
 * @DAEDALUS_DECODE_ERR_CODEC:	unknown codec_id
 */
enum daedalus_decode_status {
	DAEDALUS_DECODE_OK		= 0,
	DAEDALUS_DECODE_NO_FRAME	= 1,
	DAEDALUS_DECODE_ERR_OPEN	= 100,
	DAEDALUS_DECODE_ERR_SEND	= 101,
	DAEDALUS_DECODE_ERR_RECV	= 102,
	DAEDALUS_DECODE_ERR_CODEC	= 103,
};

/**
 * struct daedalus_resp_frame - RESP_FRAME payload
 * @status:		enum daedalus_decode_status
 * @codec_id:		echoes the request's codec_id
 * @width:		decoded frame width in pixels (0 if !OK)
 * @height:		decoded frame height in pixels (0 if !OK)
 * @pix_fmt:		libavcodec AVPixelFormat as int (informational)
 * @luma_len:		Y-plane byte count actually hashed
 * @chroma_len:		U+V byte count actually hashed (planar combined)
 * @fnv1a_yuv:		FNV-1a 32-bit hash of Y,U,V planes concatenated
 *			(line-by-line, stripping any libav alignment
 *			stride padding).  Lets the kernel side compare
 *			against an offline reference without shipping
 *			full pixel data through the chardev.
 * @reserved:		must be zero
 *
 * Fixed size — keeps wire parsing simple.  No variable-length
 * pixel data in Phase 8.4; dmabuf in Phase 8.5 carries that.
 */
struct daedalus_resp_frame {
	__u32 status;
	__u32 codec_id;
	__u32 width;
	__u32 height;
	__s32 pix_fmt;
	__u32 luma_len;
	__u32 chroma_len;
	__u32 fnv1a_yuv;
	__u32 reserved;
};

#endif /* DAEDALUS_V4L2_PROTO_H */