一，前言
动手写驱动系列将从简单到复杂，我在复习的同时，做了笔记，从小牛到大牛就是这样一步步走过来的。等我将来回头看还是很有成就感的，同时给要系统学习的同学一个学习路线的参考方向。
在动手写linux驱动(1)--Apple的学习笔记后，今天在工程3中添加ioctl和llseek。在工程4中将设备创建为3个并且驱动中添加互斥锁。
代码工程放在我gitee上https://gitee.com/applecai/linux-driver-study
二，问题记录
- unlocked_ioctl对应的宏定义参考了ioctl-number.rst，找了个没有用的0xB7。
- 添加llseek，主要应用了ppos参数。一开始当个命令测试了，即打开文件操作单独命令后关闭文件，所以ppos一直为0。因为打开后就关闭fd。后来修改了代码，实现连续操作。
- 多设备创建后无法释放导致卸载模块再重新加载后出现oop，这是因为__exit中的参数设置不对。
- APP程序调用open返回失败。因为setup_dev那个函数传的参数中index应该从6开始。虽然表明看sys/class及device都是6,7,8。但是cdev_add的inode是不对的。
- APP程序调用参数为dev7或者dev8不正确会死。但dev6则正确，原因是kmalloc申请空间的时候没有乘以3。
三，测试效果
工程3的效果：
APP中的lseek操作为retvalue = lseek(fd, -6, APPLEPAPER_CUR_POS); 写入后指针为18，此句代码的含义是指针从当前位置向前移动6个位置。我写入Apple's usr data!向前移动6个位置后再开始读取，测试通过如下：
# ./applepaper3 /dev/applepaper6
goto file applepaperApp3.c,line 88[ 63.427014] applepaper is set to zero
start to write usrdata:Apple's usr data!
[ 63.434079] written 18 bytes(s) from 0
[ 63.441267] filp->f_pos=12
[ 63.441280] read 18 bytes(s) from 12
In the end,read data:data!
retvalue = lseek(fd, 8, APPLEPAPER_BEGIN_POS);写入后指针为18，此句代码的含义是指针从开始位置向后移动8个位置。我写入Apple's usr data!则从第8个位置后再开始读取，测试通过如下：
# ./applepaper3 /dev/applepaper6
goto file applepaperApp3.c,line 88[ 90.183172] applepaper is set to zero
start to write usrdata:Apple's usr data!
[ 90.189684] written 18 bytes(s) from 0
[ 90.198539] filp->f_pos=8
[ 90.198562] read 18 bytes(s) from 8
In the end,read data:usr data!
工程4的效果
工程4包括2个锁的宏定义(打开1个即可)，一种是open/close的时候使用锁，代表文件不能同时打开。将宏定义FILE_LOCK设置为1即可APP和driver都设置为1。效果如下，说明要等第一次运行close后才能再次打开设备文件。
# ./applepaper4 /dev/applepaper6 &
# goto file applepaperApp4.c,line 88[ 140.730968] applepaper is set to zero
start to write usrdata:Apple's usr data!
[ 140.737775] written 18 bytes(s) from 0
[ 140.746198] filp->f_pos=8
[ 140.746219] read 18 bytes(s) from 8
In the end,read data:usr data!
./applepaper4App running times:1
/dev/applepaperApp running times:2
6
App running times:3
App running times:4
App running times:5
App running times:6[ 170.756126] applepaper is set to zero
goto file applepaperApp4.c,line 88
start to write usrdata:App[ 170.760564] written 18 bytes(s) from 0
le's usr data!
[ 170.771010] filp->f_pos=8
[ 170.771030] read 18 bytes(s) from 8
In the end,read data:usr data!
[ 175.522953] random: crng init done
App running times:1
App running times:2
App running times:3
App running times:4
App running times:5
App running times:6
[1]+ Done ./applepaper4 /dev/applepaper6
还有一个宏定义FILEOP_LOCK设置为1，代表读写即擦除过程加锁。driver中设置宏定义即可。效果如下，做了个sh脚本./run.sh让一个在后台运行，一个在前台运行。这个看起来不明显。
# insmod applepaper4.ko
[ 21.523194] applepaper4: loading out-of-tree module taints kernel.
[ 21.530767] Registered character driver
[ 21.536164] Registered character driver
[ 21.540895] Registered character driver
# ./applepaper4 /dev/applepaper6
goto file applepaperApp4.c,line 88[ 33.450871] applepaper is set to zero
start to write usrdata:Apple's usr data!
[ 33.457846] written 18 bytes(s) from 0
[ 33.466101] filp->f_pos=8
[ 33.466118] read 18 bytes(s) from 8
In the end,read data:usr data!
# ./run.sh
run one in backgroup,run other in console
goto file applepaperApp4.c,line 88[ 38.516497] applepaper is set to zero
start to write usrdata:Apple's usr data!
[ 38.525298] applepaper is set to zero
goto file applepaperApp4.c,line 88
start to write usrdata:Apple[ 38.530707] written 18 bytes(s) from 0
's usr data!
[ 38.541227] written 18 bytes(s) from 0
[ 38.545911] filp->f_pos=8
[ 38.545928] read 18 bytes(s) from 8
In the end,read data:usr data!
# [ 38.555957] filp->f_pos=8
[ 38.555979] read 18 bytes(s) from 8
In the end,read data:usr data!
