# Linux 核心專題: 虛擬攝影機裝置驅動程式
> 執行人: hankTaro
> [專題解說錄影](https://youtu.be/Ze4QXG0Ov9I)

:::success
:question: 提問清單
* ?
:::

## 任務簡述

[vcam](https://github.com/sysprog21/vcam) 是個針對 Linux 核心開發的虛擬攝影機裝置，全部程式碼僅 1 千 5 百行，從而可理解 V4L2 (video fro Linux APIs, version 2) 的使用和 Linux 多媒體架構。

## TODO: 整理過往報告

閱讀以下報告，並針對 Linux v5.15+ 的 [V4L2 介面](https://www.kernel.org/doc/html/latest/driver-api/media/) (及異動)，予以更新，應包含 V4L2 和 [vcam](https://github.com/sysprog21/vcam) 運作原理，可善用 [HackMD 書本模式](https://hackmd.io/s/how-to-create-book-tw)展現。
* [2020 年開發紀錄](https://hackmd.io/@eecheng/B16rQ3GjU)
* [2021 年開發紀錄](https://hackmd.io/@WayneLin1992/HkDBmLUDO)
* [2022 年開發紀錄](https://hackmd.io/@Masamaloka/linux2022-vcam)

可沿用過去的內容，但應該在整理的材料開頭提及貢獻者。紀錄你的認知和疑惑。

### V4L2 架構與簡介

V4L2 全名為 video for linux two ，前身為 V4L ，故 V4L2 尾端的 2 是2代的概念

V4L2 是 linux 中的一個驅動程式框架，其作為 API 支援實時(realtime)影音捕捉，他提供不同硬體一個統一的框架，像是你電腦的攝影機與螢幕之間，sensor 獲取了資料，要如何處理這些資料、怎麼傳輸、傳輸到哪，都是在 V4L2 的框架下統一管理。

為何需要一個這樣的框架去界在裝置與裝置之間，因為在過去不同裝置之間會需要有個別的驅動程序來供其運作，這是一件耗時且困難的工作，也容易使得裝置不正確運作，並且許多通用的代碼由於沒有共同框架，在[代碼重構](https://en.wikipedia.org/wiki/Code_refactoring)上會十分困難，故 V4L2 提供一個驅動框架收錄了各類驅動所需的基礎架構塊(basic building blocks)，可以依照使用者所需選用。

在Linux 中，所有裝置都被看成一種特殊的文件，可以像訪問一般文件一樣對其進行讀寫。像是筆電的攝影機就是在 `/dev/videoX` (其中`X`是數字，取決於有幾個註冊的攝影裝置)，V4L2 藉由對其內存映射(mmap)或直接讀取(read)來採集影像。

V4L2規範中不僅定義了通用API元素(Common API Elements)，圖像的格式(Image Formats)，輸入/輸出方法(Input/Output)，還定義了Linux內核驅動處理視頻信息的一系列接口(Interfaces)，這些接口主要有：

* 視頻採集接口——Video Capture Interface;
* 視頻輸出接口—— Video Output Interface;
* 視頻覆蓋/預覽接口——Video Overlay Interface;
* 視頻輸出覆蓋接口——Video Output Overlay Interface;
* 編解碼接口——Codec Interface。

<!-- 雖然說其名稱是 video for linux 2 ，但其應用面相十分廣泛，影片傳輸只是其中一個部份，還有包括解碼、格式轉換等等各種 -->

對於使用者來說，V4L2 的大體操作流程如下:

* Opening the device
* Changing device properties, selecting a video and audio input, video standard, picture brightness a. o.
* Negotiating a data format
* Negotiating an input/output method
* The actual input/output loop
* Closing the device

<!-- 接下來會依照 [2.4 Video device' s internal representation](https://www.kernel.org/doc/html/latest/driver-api/media/v4l2-dev.html) 來介紹如何將一新裝置藉由 V4L2 註冊進電腦 -->

<!-- #### 裝置的宣告

The actual device nodes in the /dev directory are created using the video_device struct (v4l2-dev.h). This struct can either be allocated dynamically or embedded in a larger struct.

To allocate it dynamically use video_device_alloc():

struct video_device *vdev = video_device_alloc();

if (vdev == NULL)
        return -ENOMEM;

vdev->release = video_device_release;

### v4l2 framework

<!-- ### Vcam 其作用 -->

## 確認通過 v4l2-compliance

依據 [2022 年開發紀錄](https://hackmd.io/@Masamaloka/linux2022-vcam)，確保 vcam 可通過所有 [v4l2-compliance](https://manpages.ubuntu.com/manpages/bionic/man1/v4l2-compliance.1.html) 的測試項目，若有無法通過，則逐一排除。

使用 `sudo v4l2-compliance -d /dev/video2 -f` 測試

### 5.19.0 測試結果

$ sudo v4l2-compliance -d /dev/video2 -f
v4l2-compliance 1.22.1, 64 bits, 64-bit time_t

Compliance test for vcam device /dev/video2:

Driver Info:
	Driver name      : vcam
	Card type        : vcam
	Bus info         : platform: virtual
	Driver version   : 5.19.17
	Capabilities     : 0x85200001
		Video Capture
		Read/Write
		Streaming
		Extended Pix Format
		Device Capabilities
	Device Caps      : 0x05200001
		Video Capture
		Read/Write
		Streaming
		Extended Pix Format

Required ioctls:
	test VIDIOC_QUERYCAP: OK
	test invalid ioctls: OK

Allow for multiple opens:
	test second /dev/video2 open: OK
	test VIDIOC_QUERYCAP: OK
	test VIDIOC_G/S_PRIORITY: OK
	test for unlimited opens: OK

Debug ioctls:
	test VIDIOC_DBG_G/S_REGISTER: OK (Not Supported)
	test VIDIOC_LOG_STATUS: OK (Not Supported)

Input ioctls:
	test VIDIOC_G/S_TUNER/ENUM_FREQ_BANDS: OK (Not Supported)
	test VIDIOC_G/S_FREQUENCY: OK (Not Supported)
	test VIDIOC_S_HW_FREQ_SEEK: OK (Not Supported)
	test VIDIOC_ENUMAUDIO: OK (Not Supported)
	test VIDIOC_G/S/ENUMINPUT: OK
	test VIDIOC_G/S_AUDIO: OK (Not Supported)
	Inputs: 1 Audio Inputs: 0 Tuners: 0

Output ioctls:
	test VIDIOC_G/S_MODULATOR: OK (Not Supported)
	test VIDIOC_G/S_FREQUENCY: OK (Not Supported)
	test VIDIOC_ENUMAUDOUT: OK (Not Supported)
	test VIDIOC_G/S/ENUMOUTPUT: OK (Not Supported)
	test VIDIOC_G/S_AUDOUT: OK (Not Supported)
	Outputs: 0 Audio Outputs: 0 Modulators: 0

Input/Output configuration ioctls:
	test VIDIOC_ENUM/G/S/QUERY_STD: OK (Not Supported)
	test VIDIOC_ENUM/G/S/QUERY_DV_TIMINGS: OK (Not Supported)
	test VIDIOC_DV_TIMINGS_CAP: OK (Not Supported)
	test VIDIOC_G/S_EDID: OK (Not Supported)

Control ioctls (Input 0):
	test VIDIOC_QUERY_EXT_CTRL/QUERYMENU: OK (Not Supported)
	test VIDIOC_QUERYCTRL: OK (Not Supported)
	test VIDIOC_G/S_CTRL: OK (Not Supported)
	test VIDIOC_G/S/TRY_EXT_CTRLS: OK (Not Supported)
	test VIDIOC_(UN)SUBSCRIBE_EVENT/DQEVENT: OK (Not Supported)
	test VIDIOC_G/S_JPEGCOMP: OK (Not Supported)
	Standard Controls: 0 Private Controls: 0

Format ioctls (Input 0):
	test VIDIOC_ENUM_FMT/FRAMESIZES/FRAMEINTERVALS: OK
	test VIDIOC_G/S_PARM: OK
	test VIDIOC_G_FBUF: OK (Not Supported)
	test VIDIOC_G_FMT: OK
	test VIDIOC_TRY_FMT: OK
	test VIDIOC_S_FMT: OK
	test VIDIOC_G_SLICED_VBI_CAP: OK (Not Supported)
	test Cropping: OK (Not Supported)
	test Composing: OK (Not Supported)
	test Scaling: OK (Not Supported)

Codec ioctls (Input 0):
	test VIDIOC_(TRY_)ENCODER_CMD: OK (Not Supported)
	test VIDIOC_G_ENC_INDEX: OK (Not Supported)
	test VIDIOC_(TRY_)DECODER_CMD: OK (Not Supported)

Buffer ioctls (Input 0):
	test VIDIOC_REQBUFS/CREATE_BUFS/QUERYBUF: OK
	test VIDIOC_EXPBUF: OK
	test Requests: OK (Not Supported)

Test input 0:

Stream using all formats:
	test MMAP for Format RGB3, Frame Size 640x480@59.94 Hz:
		Stride 1920, Field None: OK                                 
	test MMAP for Format RGB3, Frame Size 640x480@1.00 Hz:
		Stride 1920, Field None: OK                                 
Total for vcam device /dev/video2: 47, Succeeded: 47, Failed: 0, Warnings: 0

### 6.1.32 虛擬環境測試結果

root@(none):/tmp/vcam#  v4l2-compliance -d /dev/video0 -f
v4l2-compliance 1.22.1, 64 bits, 64-bit time_t

Compliance test for vcam device /dev/video0:

Driver Info:
	Driver name      : vcam
	Card type        : vcam
	Bus info         : platform: virtual
	Driver version   : 6.1.35
	Capabilities     : 0x85200001
		Video Capture
		Read/Write
		Streaming
		Extended Pix Format
		Device Capabilities
	Device Caps      : 0x05200001
		Video Capture
		Read/Write
		Streaming
		Extended Pix Format

Required ioctls:
	test VIDIOC_QUERYCAP: OK
	test invalid ioctls: OK

Allow for multiple opens:
	test second /dev/video0 open: OK
	test VIDIOC_QUERYCAP: OK
	test VIDIOC_G/S_PRIORITY: OK
	test for unlimited opens: OK

Debug ioctls:
	test VIDIOC_DBG_G/S_REGISTER: OK (Not Supported)
	test VIDIOC_LOG_STATUS: OK (Not Supported)

Input ioctls:
	test VIDIOC_G/S_TUNER/ENUM_FREQ_BANDS: OK (Not Supported)
	test VIDIOC_G/S_FREQUENCY: OK (Not Supported)
	test VIDIOC_S_HW_FREQ_SEEK: OK (Not Supported)
	test VIDIOC_ENUMAUDIO: OK (Not Supported)
	test VIDIOC_G/S/ENUMINPUT: OK
	test VIDIOC_G/S_AUDIO: OK (Not Supported)
	Inputs: 1 Audio Inputs: 0 Tuners: 0

Output ioctls:
	test VIDIOC_G/S_MODULATOR: OK (Not Supported)
	test VIDIOC_G/S_FREQUENCY: OK (Not Supported)
	test VIDIOC_ENUMAUDOUT: OK (Not Supported)
	test VIDIOC_G/S/ENUMOUTPUT: OK (Not Supported)
	test VIDIOC_G/S_AUDOUT: OK (Not Supported)
	Outputs: 0 Audio Outputs: 0 Modulators: 0

Input/Output configuration ioctls:
	test VIDIOC_ENUM/G/S/QUERY_STD: OK (Not Supported)
	test VIDIOC_ENUM/G/S/QUERY_DV_TIMINGS: OK (Not Supported)
	test VIDIOC_DV_TIMINGS_CAP: OK (Not Supported)
	test VIDIOC_G/S_EDID: OK (Not Supported)

Control ioctls (Input 0):
	test VIDIOC_QUERY_EXT_CTRL/QUERYMENU: OK (Not Supported)
	test VIDIOC_QUERYCTRL: OK (Not Supported)
	test VIDIOC_G/S_CTRL: OK (Not Supported)
	test VIDIOC_G/S/TRY_EXT_CTRLS: OK (Not Supported)
	test VIDIOC_(UN)SUBSCRIBE_EVENT/DQEVENT: OK (Not Supported)
	test VIDIOC_G/S_JPEGCOMP: OK (Not Supported)
	Standard Controls: 0 Private Controls: 0

Format ioctls (Input 0):
	test VIDIOC_ENUM_FMT/FRAMESIZES/FRAMEINTERVALS: OK
	test VIDIOC_G/S_PARM: OK
	test VIDIOC_G_FBUF: OK (Not Supported)
	test VIDIOC_G_FMT: OK
	test VIDIOC_TRY_FMT: OK
	test VIDIOC_S_FMT: OK
	test VIDIOC_G_SLICED_VBI_CAP: OK (Not Supported)
	test Cropping: OK (Not Supported)
	test Composing: OK (Not Supported)
	test Scaling: OK (Not Supported)

Codec ioctls (Input 0):
	test VIDIOC_(TRY_)ENCODER_CMD: OK (Not Supported)
	test VIDIOC_G_ENC_INDEX: OK (Not Supported)
	test VIDIOC_(TRY_)DECODER_CMD: OK (Not Supported)

Buffer ioctls (Input 0):
	test VIDIOC_REQBUFS/CREATE_BUFS/QUERYBUF: OK
	test VIDIOC_EXPBUF: OK
	test Requests: OK (Not Supported)

Test input 0:

Stream using all formats:
	test MMAP for Format RGB3, Frame Size 640x480@59.94 Hz:
		Stride 1920, Field None: OK                                 
	test MMAP for Format RGB3, Frame Size 640x480@1.00 Hz:
		Stride 1920, Field None: OK                                 
Total for vcam device /dev/video0: 47, Succeeded: 47, Failed: 0, Warnings: 0

## TODO: 排除記憶體錯誤

運用 [kmemleak](https://www.kernel.org/doc/html/latest/dev-tools/kmemleak.html) 和 [kasan](https://www.kernel.org/doc/html/latest/dev-tools/kasan.html) 排除記憶體錯誤

但是在使用 [kmemleak](https://www.kernel.org/doc/html/latest/dev-tools/kmemleak.html) 前,需要先編譯核心,使其可以運作,因為這個工具並非是正常使用者會使用到的,故開發者沒必要讓其在所有環境下都執行(另一方面也不是所有環境下都能讓此工具運做),故其只能在特定狀況下運行,而要如何打造這個環境就是首要的目標

### 打造虛擬環境

根據 [測試 Linux 核心的虛擬化環境](https://hackmd.io/@sysprog/linux-virtme) 來設定環境

在使用 virtme 選取預設核心組態並編譯階段,需要確保 CONFIG_DEBUG_INFO 在組態中有被開啟，以利後續實驗使用，並且在[kmemleak](https://www.kernel.org/doc/html/latest/dev-tools/kmemleak.html) 文件中寫到,需要先將 CONFIG_DEBUG_KMEMLEAK enable。

執行 `$ grep CONFIG_DEBUG_INFO .config` 若輸出沒有出現 `CONFIG_DEBUG_INFO=y` ,如下

CONFIG_DEBUG_INFO_NONE=y
# CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT is not set
# CONFIG_DEBUG_INFO_DWARF4 is not set
# CONFIG_DEBUG_INFO_DWARF5 is not set

會需要執行 `make menuconfig` 進行設定

6.1.x 的[CONFIG_DEBUG_INFO](https://www.kernelconfig.io/config_debug_info?q=&kernelversion=6.1.32&arch=x86)和[CONFIG_DEBUG_KMEMLEAK](https://www.kernelconfig.io/config_debug_kmemleak?arch=x86&kernelversion=6.1.32)是依照此位置


在你的抵達位置時不一定會找到 Compile the kernel with debug info 這個選項,你需要將 Debug information 設定成任一顯示方法,個人是設定成用 DWARF 4代格式顯示


隨後就會出現其選項了


隨後就出現了 `CONFIG_DEBUG_INFO=y`

$ grep CONFIG_DEBUG_INFO .config
CONFIG_DEBUG_INFO=y
# CONFIG_DEBUG_INFO_NONE is not set
# CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT is not set
CONFIG_DEBUG_INFO_DWARF4=y
# CONFIG_DEBUG_INFO_DWARF5 is not set
# CONFIG_DEBUG_INFO_REDUCED is not set
CONFIG_DEBUG_INFO_COMPRESSED=y
# CONFIG_DEBUG_INFO_SPLIT is not set


隨後等待其 make 結束（會需要一段時間),在編譯結束後，預期可見以下訊息:

Kernel: arch/x86/boot/bzImage is ready

隨後便可透過以下命令，在 QEMU 虛擬機器中啟動 Linux 核心:

$ virtme-run --kdir . --mods=auto

:::warning
要注意一點,在 virtme 中,除了/tmp 外的路徑都是唯獨的,若要寫入需要切換到 host 端
:::

> 確保 Debug Filesystem 是開啟的

### 編譯和測試核心模組

照著[測試 Linux 核心的虛擬化環境](https://hackmd.io/@sysprog/linux-virtme#%E5%88%A9%E7%94%A8-virtme-%E5%BB%BA%E7%AB%8B-Linux-%E6%A0%B8%E5%BF%83%E6%B8%AC%E8%A9%A6%E7%92%B0%E5%A2%83)中,編譯和測試核心模組的步驟,撰寫 hello.c 以及Makefile

#include <linux/init.h>
#include <linux/module.h>
MODULE_LICENSE("GPL");

static int hello_init(void)
{
    printk(KERN_ALERT "Hello World! - init\n");
    return 0;
}

static void hello_exit(void)
{
    printk(KERN_ALERT "Hello World! - exit\n");
}

module_init(hello_init);
module_exit(hello_exit);

KDIR=/home/ubuntu/linux

obj-m += hello.o

PWD := $(shell pwd)

all:
    $(MAKE) -C $(KDIR) M=$(PWD) modules
clean:
    $(MAKE) -C $(KDIR) M=$(PWD) clean

:::warning
在[測試 Linux 核心的虛擬化環境](https://hackmd.io/@sysprog/linux-virtme#%E5%88%A9%E7%94%A8-virtme-%E5%BB%BA%E7%AB%8B-Linux-%E6%A0%B8%E5%BF%83%E6%B8%AC%E8%A9%A6%E7%92%B0%E5%A2%83)中， Makefile 的代碼有誤
`KDIR := $(PWD)/..` 這行會導致 KDIR 導引到錯誤位置,故將其刪除

以及要將 `KDIR=/home/ubuntu/linux` 設定為自己存放虛擬環境的目錄
:::

# make
make -C /home/hank/linux2023/virtme/linux M=/tmp/hello modules
make[1]: Entering directory '/home/hank/linux2023/virtme/linux'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: x86_64-linux-gnu-gcc (Ubuntu 11.3.0-1ubuntu1~22.04.1) 11.3.0
  You are using:           gcc (Ubuntu 11.3.0-1ubuntu1~22.04.1) 11.3.0
  CC [M]  /tmp/hello/hello.o
  MODPOST /tmp/hello/Module.symvers
  CC [M]  /tmp/hello/hello.mod.o
  LD [M]  /tmp/hello/hello.ko
make[1]: Leaving directory '/home/hank/linux2023/virtme/linux'

隨後便可測試載入以及移除模組

# insmod hello.ko 
[  902.474833] Hello World! - init

# rmmod hello 
[  934.470132] Hello World! - exit

### 嘗試建立 ko 檔

因為 vcam 需要 videobuf2-vmalloc videobuf2-v4l2 兩個核心模組作為前製,

$ sudo make modules_install modules=videobuf2-vmalloc
[sudo] hank 的密碼： 
make[1]: *** 沒有規則可製作目標「videobuf2-vmalloc」，由「__modinst」 需求。 停止。
make: *** [Makefile:1941：modules_install] 錯誤 2

發現 make modules 也只有少少幾個 ko 檔被編譯出來

$ make modules
  UPD     include/generated/compile.h
  CC      scripts/mod/empty.o
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/modpost.o
  CC      scripts/mod/devicetable-offsets.s
  HOSTCC  scripts/mod/file2alias.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTLD  scripts/mod/modpost
  CC      kernel/bounds.s
  CC      arch/x86/kernel/asm-offsets.s
  CALL    scripts/checksyscalls.sh
  DESCEND objtool
  CC [M]  fs/efivarfs/inode.o
  CC [M]  fs/efivarfs/file.o
  CC [M]  fs/efivarfs/super.o
  CC [M]  fs/efivarfs/vars.o
  LD [M]  fs/efivarfs/efivarfs.o
  CC [M]  drivers/thermal/intel/x86_pkg_temp_thermal.o
  CC [M]  net/netfilter/nf_log_syslog.o
  CC [M]  net/netfilter/xt_mark.o
  CC [M]  net/netfilter/xt_nat.o
  CC [M]  net/netfilter/xt_LOG.o
  CC [M]  net/netfilter/xt_MASQUERADE.o
  CC [M]  net/netfilter/xt_addrtype.o
  CC [M]  net/ipv4/netfilter/iptable_nat.o
  MODPOST Module.symvers
  LDS     scripts/module.lds
  CC [M]  drivers/thermal/intel/x86_pkg_temp_thermal.mod.o
  LD [M]  drivers/thermal/intel/x86_pkg_temp_thermal.ko
  CC [M]  fs/efivarfs/efivarfs.mod.o
  LD [M]  fs/efivarfs/efivarfs.ko
  CC [M]  net/ipv4/netfilter/iptable_nat.mod.o
  LD [M]  net/ipv4/netfilter/iptable_nat.ko
  CC [M]  net/netfilter/nf_log_syslog.mod.o
  LD [M]  net/netfilter/nf_log_syslog.ko
  CC [M]  net/netfilter/xt_LOG.mod.o
  LD [M]  net/netfilter/xt_LOG.ko
  CC [M]  net/netfilter/xt_MASQUERADE.mod.o
  LD [M]  net/netfilter/xt_MASQUERADE.ko
  CC [M]  net/netfilter/xt_addrtype.mod.o
  LD [M]  net/netfilter/xt_addrtype.ko
  CC [M]  net/netfilter/xt_mark.mod.o
  LD [M]  net/netfilter/xt_mark.ko
  CC [M]  net/netfilter/xt_nat.mod.o
  LD [M]  net/netfilter/xt_nat.ko

<!-- 在 virtme 中無法裝上 v4l2 模組，因為 `/lib/modules/6.3.12/kernel/driver` 中並沒有 media 的目錄

/lib/modules/6.1.32/kernel/drivers$ ls -a
.  ..  thermal

<!-- 使用 `modinfo` 確認在 host 端所載入的模組位置,確認其是在 `/lib/modules/5.19.0-45-generic/kernel/drivers/media/common/videobuf2/videobuf2-v4l2.ko` 中,這是在 6.3.12 中沒有的路徑,接來就是要想辦法去建構出 6.3.12 版的 videobuf2-v4l2.ko 來

$ modinfo videobuf2-v4l2 
filename:       /lib/modules/5.19.0-45-generic/kernel/drivers/media/common/videobuf2/videobuf2-v4l2.ko

https://www.kernel.org/doc/Documentation/kbuild/kbuild.txt -->

<!-- 由於原先使用的版本是5.19.0,而虛擬環境是6.1.32,所以在 `lib/modules` 中並沒有 6.1.32 的目錄與相關文件,故在 makefile 中的 `modules_install` target 會變成建立一個 6.1.32 的目錄,並且將 `modules.oreder` 的 ko 檔加入原本的目錄(也就是於只有`modules.oreder` 中的 ko 檔會被建立)

modules_install: $(modinst_pre)
PHONY += __modinst_pre
__modinst_pre:
	@rm -rf $(MODLIB)/kernel
	@rm -f $(MODLIB)/source
	@mkdir -p $(MODLIB)/kernel
	@ln -s $(abspath $(srctree)) $(MODLIB)/source
	@if [ ! $(objtree) -ef  $(MODLIB)/build ]; then \
		rm -f $(MODLIB)/build ; \
		ln -s $(CURDIR) $(MODLIB)/build ; \
	fi
	@sed 's:^:kernel/:' modules.order > $(MODLIB)/modules.order
	@cp -f modules.builtin $(MODLIB)/
	@cp -f $(objtree)/modules.builtin.modinfo $(MODLIB)/

endif # CONFIG_MODULES

在與教授討論並重新詳閱 kernelconfig 加上反覆驗證後，得知需要在編譯核心時設定 [`CONFIG_MEDIA_SUPPORT = y`](https://www.kernelconfig.io/CONFIG_MEDIA_SUPPORT?kernelversion=6.1.35) 才會編譯出相關的 ko 檔

> [videobuf2-vmalloc.ko](https://www.kernelconfig.io/CONFIG_VIDEOBUF_VMALLOC?kernelversion=6.1.35) 與 [videobuf2-v4l2.ko](https://www.kernelconfig.io/CONFIG_VIDEOBUF2_V4L2?q=videobuf2-v4l2.ko&kernelversion=6.1.35&arch=x86) 都依賴於此

<!-- 
一開始裡面的東西很少,要將 Media device type 內的選項全選才會多出許多選項

 -->

使用 `/` 搜尋 VIDEOBUF2_V4L2,找出使其 enable 的設定

> 需要將自動選擇附加功能的這個選項關掉


隨後 make 完使用 make modules_install ,便可見到需要的那兩個 ko 檔

root@(none):/# modprobe videobuf2_v4l2 videobuf2_vmalloc
root@(none):/# lsmod
Module                  Size  Used by
videobuf2_vmalloc      16384  0
videobuf2_memops       16384  1 videobuf2_vmalloc
videobuf2_v4l2         36864  0
videobuf2_common       65536  3 videobuf2_vmalloc,videobuf2_v4l2,videobuf2_memops

架設成功

### 嘗試在虛擬環境中 make vcam

root@(none):/tmp/vcam# make
make -C /lib/modules/6.1.35/build M=/tmp/vcam modules
make[1]: Entering directory '/home/hank/linux2023/virtme/linux'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: x86_64-linux-gnu-gcc (Ubuntu 11.3.0-1ubuntu1~22.04.1) 11.3.0
  You are using:           gcc (Ubuntu 11.3.0-1ubuntu1~22.04.1) 11.3.0
  CC [M]  /tmp/vcam/module.o
  CC [M]  /tmp/vcam/control.o
...
[  190.819560] Tasks state (memory values in pages):
[  190.819844] [  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name
[  190.820366] [     98]     0    98     5780      528    61440        0             0 systemd-udevd
[  190.820890] [    163]     0   163     1193      151    45056        0             0 bash
[  190.821362] [    169]     0   169      795       77    45056        0             0 make
[  190.821871] [    171]     0   171      879      165    45056        0             0 make
[  190.822344] [    386]     0   386      897      169    45056        0             0 make
[  190.822821] [    409]     0   409      724       38    49152        0             0 sh
[  190.823284] [    410]     0   410      939       43    40960        0             0 gcc
[  190.823756] [    411]     0   411    18841     9025   188416        0             0 cc1
[  190.824284] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,task=cc1,pid=411,uid=0
[  190.824992] Out of memory: Killed process 411 (cc1) total-vm:75364kB, anon-rss:35828kB, file-rss:272kB, shmem-rss:0kB, UID:0 pgtables:184kB oom_score_adj:0
gcc: fatal error: Killed signal terminated program cc1
compilation terminated.
make[2]: *** [scripts/Makefile.build:250: /tmp/vcam/control.o] Error 1
make[1]: *** [Makefile:2012: /tmp/vcam] Error 2
make[1]: Leaving directory '/home/hank/linux2023/virtme/linux'
make: *** [Makefile:14: kmod] Error 2
root@(none):/tmp/vcam# 

發生了 oom (out of memory)，由於執行 kmemleak 需要較大的記憶體,故退出虛擬環境利用`virtme-run --kdir . --mods=auto --qemu-opts -m 2048` 配置 2048 的記憶體大小

再度執行 make

root@(none):/tmp/vcam# make
make -C /lib/modules/6.1.35/build M=/tmp/vcam modules
make[1]: Entering directory '/home/hank/linux2023/virtme/linux'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: x86_64-linux-gnu-gcc (Ubuntu 11.3.0-1ubuntu1~22.04.1) 11.3.0
  You are using:           gcc (Ubuntu 11.3.0-1ubuntu1~22.04.1) 11.3.0
  CC [M]  /tmp/vcam/module.o
  CC [M]  /tmp/vcam/control.o
  CC [M]  /tmp/vcam/device.o
  CC [M]  /tmp/vcam/videobuf.o
  CC [M]  /tmp/vcam/fb.o
  LD [M]  /tmp/vcam/vcam.o
  MODPOST /tmp/vcam/Module.symvers
  CC [M]  /tmp/vcam/vcam.mod.o
  LD [M]  /tmp/vcam/vcam.ko
make[1]: Leaving directory '/home/hank/linux2023/virtme/linux'
cc -O2 -Wall -Wextra -pedantic -std=c99 -o vcam-util vcam-util.c

成功通過

隨後將 vcam.ko 架設上,並開始測試

root@(none):/tmp/vcam# insmod vcam.ko
[65600.023786] vcam: loading out-of-tree module taints kernel.
[65600.026288] Console: switching to colour frame buffer device 80x30
root@(none):/tmp/vcam# lsmod
Module                  Size  Used by
vcam                   28672  1
videobuf2_vmalloc      16384  1 vcam
videobuf2_memops       16384  1 videobuf2_vmalloc
videobuf2_v4l2         36864  1 vcam
videobuf2_common       65536  4 videobuf2_vmalloc,vcam,videobuf2_v4l2,videobuf2_memops
root@(none):/tmp/vcam# ./vcam-util -l
Available virtual V4L2 compatible devices:
1. fb0(640,480,1/1,rgb24) -> /dev/video0

### kmemleak 的使用與架設

執行 `# mount -t debugfs nodev /sys/kernel/debug/` 後,利用 `mount | grep "debug"` 確認

root@(none):/# mount | grep "debug"
debugfs on /sys/kernel/debug type debugfs (rw,relatime)

確認已成功裝上

<!-- ### 過往被砍掉的東西 -->

<!-- <s>
一開始先在 [The Linux Kernel Archives](https://www.kernel.org/) 下載 linux-6.3.5，並且解壓縮在/usr/src，依照[鳥哥的教學](https://linux.vbird.org/linux_basic/mandrake9/0540kernel-2.4.18.php)似乎是要放在/usr/src/linux，但我的目錄結構中並沒有 /usr/src/linux，而且所有的核心目錄都是在 /usr/src 中，故解壓縮到 /usr/src
</s> -->

<!-- :::warning
不需要特別解壓縮到 `/usr/src` 目錄，在一般使用者的工作目錄編譯核心即可。鳥哥的教學關於 Linux 核心編譯的描述已過時。
:notes: jserv
::: -->

<!-- 
-->

<!-- :::warning
不要裝太新的 Linux 核心 (v6.3+)，參照 [測試 Linux 核心的虛擬化環境](https://hackmd.io/@sysprog/linux-virtme) 來設定和測試。
:notes: jserv
::: -->