# 前缘
去年在淘宝上买了一个无线网卡，由于是给办公室电脑用，系统是 Windows 10 ，就买了个便宜的，只支持 Windows 和 MAC 。
期间也尝试过插在蜗牛星际上(Ubuntu Server 18.04)，只看到多了一个 usb 设备，并不能产生无线网络接口，问淘宝卖家，给了一个驱动链接
CF-811AC驱动下载地址：http://www.comfast.cn/index.php?m=content&c=index&a=show&catid=30&id=335
下载下来也没编过，结果就没在 Linux上用上。
# 再续
最近在研究 Wi-Fi ，又把它掏了出来，看看能不能在 Linux 上用起来。
直接插在树莓派上，情况还是和之前在蜗牛星际上一样，只显示多了一个 usb 设备，并没有无线网络接口产生。
网上搜到了这篇教程 《Linux安装comfast 811AC usb网卡驱动》 ，就跟着上面的步骤下载编译。
由于树莓派里面没有装内核头文件，所以编译报错，解决办法，安装内核头文件
sudo apt install raspberrypi-kernel-headers
注意，ARM 架构的话要执行 README.md 里的三句指令
sudo cp /lib/modules/$(uname -r)/build/arch/arm/Makefile /lib/modules/$(uname -r)/build/arch/arm/Makefile.$(date +%Y%m%d%H%M)
sudo sed -i 's/-msoft-float//' /lib/modules/$(uname -r)/build/arch/arm/Makefile
sudo ln -s /lib/modules/$(uname -r)/build/arch/arm /lib/modules/$(uname -r)/build/arch/armv7l
继续编译，又报错
/home/pi/project/c/DRIVERS/rtl8821CU/core/rtw_debug.c: In function ‘dump_drv_version’:
/home/pi/project/c/DRIVERS/rtl8821CU/core/rtw_debug.c:45:62: error: macro "__DATE__" might prevent reproducible builds [-Werror=date-time]
RTW_PRINT_SEL(sel, "build time: %s %s\n", __DATE__, __TIME__);
^
/home/pi/project/c/DRIVERS/rtl8821CU/core/rtw_debug.c:45:62: error: macro "__TIME__" might prevent reproducible builds [-Werror=date-time]
/home/pi/project/c/DRIVERS/rtl8821CU/core/rtw_debug.c:45:62: error: macro "__DATE__" might prevent reproducible builds [-Werror=date-time]
/home/pi/project/c/DRIVERS/rtl8821CU/core/rtw_debug.c:45:62: error: macro "__TIME__" might prevent reproducible builds [-Werror=date-time]
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:304: /home/pi/project/c/DRIVERS/rtl8821CU/core/rtw_debug.o] Error 1
make[1]: *** [Makefile:1522: _module_/home/pi/project/c/DRIVERS/rtl8821CU] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-4.19.97-v7+'
make: *** [Makefile:2217: modules] Error 2
提示没有 __TIME__ 、 __DATE__ 宏，grep查看一下哪些地方使用了这些宏
pi@raspberrypi:~/project/c/DRIVERS/rtl8821CU $ grep -rn "__DATE__"
core/rtw_debug.c:45: RTW_PRINT_SEL(sel, "build time: %s %s\n", __DATE__, __TIME__);
本来想给它手动改个时间日期填上，发现只有一句，并且感觉不是什么重要的语句，就直接注释掉了
void dump_drv_version(void *sel)
{
RTW_PRINT_SEL(sel, "%s %s\n", DRV_NAME, DRIVERVERSION);
//RTW_PRINT_SEL(sel, "build time: %s %s\n", __DATE__, __TIME__);
}
编译通过，安装到内核
pi@raspberrypi:~/project/c/DRIVERS/rtl8821CU$ sudo modprobe 8821cu
查看驱动是否安装成功
pi@raspberrypi:~/project/c/DRIVERS/rtl8821CU$ lsmod
Module Size Used by
8821cu 2404352 0
r8188eu 438272 0
lib80211 16384 1 r8188eu
nls_ascii 16384 1
btsdio 20480 0
bluetooth 557056 1 btsdio
ecdh_generic 16384 1 bluetooth
ecc 36864 1 ecdh_generic
brcmfmac 385024 0
brcmutil 24576 1 brcmfmac
bcm2835_v4l2 45056 0
bcm2835_mmal_vchiq 40960 1 bcm2835_v4l2
vc_sm_cma 45056 1 bcm2835_mmal_vchiq
v4l2_common 16384 1 bcm2835_v4l2
videobuf2_vmalloc 20480 1 bcm2835_v4l2
videobuf2_memops 20480 1 videobuf2_vmalloc
cfg80211 692224 3 r8188eu,brcmfmac,8821cu
videobuf2_v4l2 28672 1 bcm2835_v4l2
出现了 8821cu 说明驱动模块载入内核成功。
接着，拔插无线网卡，看到无线网卡已经被成功驱动，并且可以正常使用了，wlan0 是树莓派自带的无线网卡，wlan1 就是 comfast 无线网卡。
pi@raspberrypi:~/project/c/DRIVERS/rtl8821CU $ ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.2.116 netmask 255.255.255.0 broadcast 192.168.2.255
inet6 fe80::c294:4582:7476:70d5 prefixlen 64 scopeid 0x20<link>
ether b8:27:eb:8a:bc:f4 txqueuelen 1000 (Ethernet)
RX packets 1122 bytes 123550 (120.6 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 849 bytes 280450 (273.8 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 172 bytes 14084 (13.7 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 172 bytes 14084 (13.7 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.2.211 netmask 255.255.255.0 broadcast 192.168.2.255
inet6 fe80::7186:984c:b898:8ef3 prefixlen 64 scopeid 0x20<link>
ether de:88:c4:e0:37:89 txqueuelen 1000 (Ethernet)
RX packets 330 bytes 42876 (41.8 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 225 bytes 31375 (30.6 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
wlan1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.2.178 netmask 255.255.255.0 broadcast 192.168.2.255
inet6 fe80::5ca7:f148:acc7:565a prefixlen 64 scopeid 0x20<link>
ether 6e:b8:f3:2a:7b:76 txqueuelen 1000 (Ethernet)
RX packets 462 bytes 76567 (74.7 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 245 bytes 34741 (33.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0