marfrit
895f57c63a
Adds /dev/daedalus-v4l2 misc chardev to the kernel module. The
chardev is the IPC channel for the future userspace decoder
daemon: kernel enqueues REQ_* messages, daemon read()s them,
processes, write()s RESP_* back.
Wire protocol (pre-1.0, header in include/daedalus_v4l2_proto.h):
- struct daedalus_msg_hdr: magic (D04V) + version + type +
cookie + payload_len + reserved
- Request/response separated by high bit of type field
- Max 64 KiB payload per message
- Cookie correlates request with matching response
Kernel implementation (kernel/daedalus_v4l2_chardev.{c,h}):
- Single-instance chardev (-EBUSY on second open)
- In-kernel FIFO bounded at 64 messages
- Blocking + non-blocking read; poll() with EPOLLIN on queued
- write() parses + validates header, logs response at pr_debug
- Bad magic → -EBADMSG, bad version → -EPROTO, oversize → -EMSGSIZE
- All error paths free resources
Phase 8.2 test trigger via debugfs:
- /sys/kernel/debug/daedalus_v4l2/test_ping — any byte
enqueues a PING with a fixed 24-byte payload. Removed in
Phase 8.4 when real REQ_DECODE from V4L2 path takes over.
Userspace verification tool (tools/test_chardev_pingpong.c):
- Real C program, proper error reporting via strerror
- Validates the 6-step round-trip: open → empty-queue EAGAIN →
trigger ping → read PING → verify all fields → write PONG → close
- Builds with -Wall -Wextra clean
Verification on hertz (Pi 5, 6.12.75+rpt-rpi-2712):
$ sudo insmod daedalus_v4l2.ko
$ sudo tools/test_chardev_pingpong
opening /dev/daedalus-v4l2...
non-blocking read on empty queue: EAGAIN ✓
injected PING via debugfs ✓
read PING: magic ✓ version ✓ type=PING ✓ cookie=0x1234 ✓ payload=24 bytes
payload: "DAEDALUS-V4L2-PING-PL"
wrote PONG (cookie=0x1234) ✓
ALL TESTS PASSED.
$ sudo rmmod daedalus_v4l2 # clean
Per correctness-before-speed: full kerneldoc on structs, 8-tab
kernel style, SPDX headers, proper error paths, real test
program (not "I ran it once"), failure-mode coverage documented.
Phase 8.3 next: userspace daemon with dlopen'd FFmpeg parse path.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
48 lines
1.3 KiB
Makefile
48 lines
1.3 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0-or-later
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#
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# daedalus-v4l2 — out-of-tree kbuild for the Linux kernel V4L2
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# stateless decoder shim. Forwards bitstream + controls to the
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# daedalus-v4l2 userspace daemon via a chardev bridge.
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#
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# Build against the running kernel:
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# make
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# Or against a specific kernel:
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# make KERNELDIR=/path/to/kernel/source
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# Install (requires root):
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# sudo make install
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# Clean:
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# make clean
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obj-m := daedalus_v4l2.o
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daedalus_v4l2-objs := daedalus_v4l2_main.o daedalus_v4l2_chardev.o
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KERNELDIR ?= /lib/modules/$(shell uname -r)/build
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PWD := $(shell pwd)
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# Be strict: warnings are errors, kernel coding style enforced.
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# include/ is for the shared kernel↔daemon wire protocol header.
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ccflags-y := -Wall -Wextra -Wno-unused-parameter -I$(src)/../include
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all:
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$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
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install: all
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$(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install
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depmod -a
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clean:
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$(MAKE) -C $(KERNELDIR) M=$(PWD) clean
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# Run kernel checkpatch.pl against the source. Picks up the
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# kernel-tree-installed checkpatch via the running kernel's
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# build directory if present.
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checkpatch:
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@if [ -x $(KERNELDIR)/scripts/checkpatch.pl ]; then \
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$(KERNELDIR)/scripts/checkpatch.pl --no-tree --strict -f *.c; \
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else \
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echo "checkpatch.pl not available at $(KERNELDIR)/scripts/"; \
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exit 1; \
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fi
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.PHONY: all install clean checkpatch
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