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xv6's Introduction
1.启动xv6在上个md文件已经写过了 2.如何提交以及评分也写过了 3.准备工作 实现sleep函数在xv6上，功能和unix的sleep一样，然后这个函数的参数是用户指定的一个数，这个数的单位是xv6内核提供的，是计时器两次中断的时间差值。然后这个函数被定义在user/sleep.c里面。 我们先不着急编写代码，先去目录下看看有什么，如何在vscode远程打开服务器文件请看上一章。  文件看起来很乱，因为编译生成了一堆中间文件编译结果，所以先清理一下,使用make clean 额结果还是很乱  带有out的先不管，应该是生成文件，LICENSE是版权声明，Makefile是cmake编译的配置文件，gradelib.py应该是执行make grade的脚本文件，也就是评分文件，先不用管。4个文件夹，conf应该是配置  kernel是内核文件，现在也应该用不到  mkfs文件夹，查了一下这个命令在linux上是，*mkfs*(英文全拼:make file system)命令用于在特定的分区上建立 linux 文件系统。同时观察到main函数也在里面，或许系统便是从这开始启动的。  最后一个文件夹便是user，也是本次实验的目标文件夹。我们要在里面实现sleep函数，然后发现没有sleep.c这个文件，结合user.h重的声明与文件夹的函数定义来看。应该是自己定义一个sllep文件，并实现user.h的声明。  4.实现sleep - Before you start coding, read Chapter 1 of the [xv6 book](https://pdos.csail.mit.edu/6.828/2020/xv6/book-riscv-rev1.pdf). - Look at some of the other programs in `user/` (e.g., `user/echo.c`, `user/grep.c`, and `user/rm.c`) to see how you can obtain the command-line arguments passed to a program. - If the user forgets to pass an argument, sleep should print an error message. - The command-line argument is passed as a string; you can convert it to an integer using `atoi` (see user/ulib.c). - Use the system call `sleep`. - See `kernel/sysproc.c` for the xv6 kernel code that implements the `sleep` system call (look for `sys_sleep`), `user/user.h` for the C definition of `sleep` callable from a user program, and `user/usys.S` for the assembler code that jumps from user code into the kernel for `sleep`. - Make sure `main` calls `exit()` in order to exit your program. - Add your `sleep` program to `UPROGS` in Makefile; once you've done that, `make qemu` will compile your program and you'll be able to run it from the xv6 shell. - Look at Kernighan and Ritchie's book *The C programming language (second edition)* (K&R) to learn about C. 官方给了我们一些建议， 1.做之前读xv6的第一章https://pdos.csail.mit.edu/6.828/2020/xv6/book-riscv-rev1.pdf 2.看一下其他函数怎么实现的，怎么读取命令行参数 3.如果没有参数，我们实现的sleep应该报错 4.如果是参数是string，应该使用user/ulib.c的atoi函数转为数字 5.使用系统调用在kernel/sysproc.c文件里面的sys_sleep函数。然后是.s文件是用户代码向系统调用跳转的桥梁 6.确保exit()能够离开程序 7.将写的sleep.c添加到makefile里面确保被编译 8.多读读c语言看看咋写 ```c // system calls int sleep(int n) Pause for n clock ticks. //使用这个系统调用 ``` 然后观察sys_sleep函数 ```c uint64 sys_sleep(void) // /kernel/sysproc.c { int n; uint ticks0; if(argint(0, &n) < 0) return -1; acquire(&tickslock); ticks0 = ticks; while(ticks - ticks0 < n){ if(myproc()->killed){ release(&tickslock); return -1; } sleep(&ticks, &tickslock); } release(&tickslock); return 0; } int atoi(const char *s) // path: /user/ulib.c { int n; n = 0; while('0' <= *s && *s <= '9') n = n*10 + *s++ - '0'; return n; } //kill.c 看看人家咋写的 int main(int argc, char **argv) { int i; if(argc < 2){ fprintf(2, "usage: kill pid...\n"); exit(1); } for(i=1; i<argc; i++) kill(atoi(argv[i])); exit(0); } int atoi(const char *s) { int n; n = 0; while('0' <= *s && *s <= '9') n = n*10 + *s++ - '0'; return n; } ``` argc 是参数的个数，argv是参数的数组。例如 sleep 7 则argc等于2 然后argv[0]=sleep argue[1]=7 atoi函数会把字符转为数字，如果是非数字字符则返回一个0，不满足条件跳出while循环，n被赋初值0. 然后代码如下 ```c #include "kernel/types.h" #include "kernel/stat.h" #include "user/user.h" int main(int argc, char **argv) { int ticks; if(argc!=2 || argv[1]==0) { fprintf(2, "usage: args is error\n"); exit(1); } ticks=atoi(argv[1]); sleep(ticks); exit(0); } ``` 注意：include的顺序，我怀疑他gcc版本太低，导致include顺序不对会链接失败！！！例如 ```c #include "kernel/stat.h" #include "user/user.h" #include "kernel/types.h" //按如上顺序编译连接会出现如下错误 In file included from user/sleep.c:1: ./kernel/stat.h:7:3: error: unknown type name ‘uint’ 7 | uint ino; // Inode number | ^~~~ ./kernel/stat.h:10:3: error: unknown type name ‘uint64’ 10 | uint64 size; // Size of file in bytes | ^~~~~~ In file included from user/sleep.c:2: ./user/user.h:36:1: error: unknown type name ‘uint’; did you mean ‘int’? 36 | uint strlen(const char*); | ^~~~ | int ./user/user.h:37:26: error: unknown type name ‘uint’; did you mean ‘int’? 37 | void* memset(void*, int, uint); | ^~~~ | int ./user/user.h:38:1: error: parameter names (without types) in function declaration [-Werror] 38 | void* malloc(uint); | ^~~~ ./user/user.h:41:40: error: unknown type name ‘uint’; did you mean ‘int’? 41 | int memcmp(const void *, const void *, uint); | ^~~~ | int ./user/user.h:42:36: error: unknown type name ‘uint’; did you mean ‘int’? 42 | void *memcpy(void *, const void *, uint); | ^~~~ | int cc1: all warnings being treated as errors ``` 个人认为因为 uint的定义在types.c定义 而user.c使用了types.c的定义，所以应该先链接types.c再链接user,c。然后因为stat.h使用了types.c的定义的东西所以应该先引用types.c 然后引用 stat.c 最后引用user.h 不知道理解正确不正确。当然如果直接抄其他函数的定义应该就遇不到这个错误了。现在编码几乎没遇到过这种问题。咔咔一堆引用就完事了。因为我印象里面老的c语言版本好像是只能在开头定义变量，然后实验了一下在任何地方都能定义变量。应该不是老版c语言规则。 编写完函数别忘了在makefile里面添加上去，要不然cmake是不会识别的。 ```makefile UPROGS=\ $U/_cat\ $U/_echo\ $U/_forktest\ $U/_grep\ $U/_init\ $U/_kill\ $U/_ln\ $U/_ls\ $U/_mkdir\ $U/_rm\ $U/_sh\ $U/_stressfs\ $U/_usertests\ $U/_grind\ $U/_wc\ $U/_zombie\ $U/_sleep\ ``` 然后启动xv6，输入ls命令可以看到我们写的sleep命令了就  最后测一下我们写的代码能不能通过测试 方式一 ```shell make GRADEFLAGS=sleep grade make[1]: Leaving directory '/home/ubuntu/xv6-labs-2020' == Test sleep, no arguments == sleep, no arguments: OK (2.9s) == Test sleep, returns == sleep, returns: OK (0.6s) == Test sleep, makes syscall == sleep, makes syscall: OK (0.9s) ``` 方式二 ```shell ./grade-lab-util sleep make: 'kernel/kernel' is up to date. == Test sleep, no arguments == sleep, no arguments: OK (0.7s) == Test sleep, returns == sleep, returns: OK (1.2s) == Test sleep, makes syscall == sleep, makes syscall: OK (0.9s) ``` 方式三 ```shell make grade == Test sleep, no arguments == $ make qemu-gdb sleep, no arguments: OK (2.5s) == Test sleep, returns == $ make qemu-gdb sleep, returns: OK (0.8s) == Test sleep, makes syscall == $ make qemu-gdb sleep, makes syscall: OK (0.8s) == Test pingpong == $ make qemu-gdb pingpong: FAIL (1.2s) ... $ pingpong exec pingpong failed $ echo OK GOOD OK $ qemu-system-riscv64: terminating on signal 15 from pid 214185 (make) MISSING '^\d+: received ping$' MISSING '^\d+: received pong$' QEMU output saved to xv6.out.pingpong == Test primes == $ make qemu-gdb primes: FAIL (0.9s) ... $ primes exec primes failed $ echo OK GOOD OK $ qemu-system-riscv64: terminating on signal 15 from pid 214218 (make) MISSING 'prime 2' MISSING 'prime 3' MISSING 'prime 5' MISSING 'prime 7' MISSING 'prime 11' MISSING 'prime 13' MISSING 'prime 17' MISSING 'prime 19' MISSING 'prime 23' MISSING 'prime 29' MISSING 'prime 31' QEMU output saved to xv6.out.primes == Test find, in current directory == ``` ## pingpong 编写一个pingpong程序，和sleep一样位于user/pingpong.c。功能是fork一个子进程，然后可以双向传输数据。当子进程收到父进程传输的数据的时候应该输出如下格式：“<pid>: received ping” pid是该进程的pid。然后给父进程发送数据后结束本身。父进程收到数据后应该输出如下格式：“<pid>: received pong”，下面是给的提示。 - Use `pipe` to create a pipe. 使用pipe创建管道 - Use `fork` to create a child. 使用fork创建子进程 - Use `read` to read from the pipe, and `write` to write to the pipe. 用read读出管道数据，用write写数据向管道 - Use `getpid` to find the process ID of the calling process. 用find找到所属pid - Add the program to `UPROGS` in Makefile. 将文件添加到makefile - User programs on xv6 have a limited set of library functions available to them. You can see the list in `user/user.h`; the source (other than for system calls) is in `user/ulib.c`, `user/printf.c`, and `user/umalloc.c`. 只能使用xv6提供的函数，可以在user.h和剩下的文件里面找到。 ```c int write(int fd, char *buf, int n) Write n bytes from buf to file descriptor fd; returns n. int read(int fd, char *buf, int n) Read n bytes into buf; returns number read; or 0 if end of file. int close(int fd) Release open file fd. int pipe(int p[]) Create a pipe, put read/write file descriptors in p[0] and p[1]. ``` 一开始没搞清楚close在pipe上的用法，写完就关闭写端导致无法继续写入报错。读完关闭读端导致读失败。因为父进程和子进程共用一个pipe所以不用关闭但要分时使用pipe，或者创建两个pipe将半双工改造成全双工。**注意一定要用sleep岔开子进程与父进程的运行，printf或者fprintf是可以被中断的，会一起打印一些东西** ```c #include "kernel/types.h" #include "kernel/stat.h" #include "user/user.h" int main(int argc, char **argv) { //no use args if(argc!=1) { fprintf(2, "usage: args is error\n"); exit(1); } int p_c_fd[2]; //fd[0] --read fd[1] --write int c_p_fd[2]; //fd[0] --read fd[1] --write if(pipe(p_c_fd)!=0 || pipe(c_p_fd)!=0) { fprintf(2, "usage: create pipe faild!\n"); exit(1); } int pid=fork(); if(pid<0) //创建失败 { fprintf(2, "usage: create process faild!\n"); exit(1); } else if(pid==0) //子进程 { sleep(10); char buf[255]; char *msg="pong"; if(read(p_c_fd[0], buf, sizeof(buf))==-1) { fprintf(2, "%d: read faild!\n",getpid()); exit(1); } printf("%d: received ping\n",getpid()); if(write(c_p_fd[1], msg, strlen(msg))==-1) { fprintf(2, "%d: write faild!\n",getpid()); exit(1); } exit(0); } else //父进程 { char buf[255]; char *msg="ping"; if(write(p_c_fd[1], msg, strlen(msg))==-1) { fprintf(2, "%d: write faild!\n",getpid()); exit(1); } sleep(30); if(read(c_p_fd[0], buf, sizeof(buf))==-1) { fprintf(2, "%d: read faild!\n",getpid()); exit(1); } printf("%d: received pong\n",getpid()); exit(0); } exit(0); } ``` ## 2.4 管道读写规则[#](https://www.cnblogs.com/Grong/p/15630119.html#24-管道读写规则) 用阻塞的方式打开管道（即默认情况下） 1. 如果**所有管道写端对应的文件描述符被关闭**（管道写端引用计数为 0），读端在将管道中剩余数据读取后，再次**read会返回0**。（写端关闭） 2. 如果**有指向管道写端的文件描述符没关闭**，且持有管道**写端的进程也没有向管道中写数据**，这时有进程从管道读端读数据，那么管道中剩余的数据都被读取后，再次 **read 会阻塞**。（读完不写） 3. 如果**所有指向管道读端的文件描述符都关闭了**（管道读端引用计数为 0），进行write操作会产生信号SIGPIPE,进而可能导致write进程退出。（读端关闭） 4. 如果**有指向管道读端的文件描述符没关闭**（管道读端引用计数大于 0），且**读端进程并没有向管道中读进程**，则当写端进程写满后，会进入阻塞。（写满不读） ## 2.5 管道的特点[#](https://www.cnblogs.com/Grong/p/15630119.html#25-管道的特点) - 只能用于具有共同祖先的进程（具有亲缘关系的进程）之间进行通信。 - 管道提供流式服务。 - 管道的生命周期随进程，进程退出，管道释放。 - 内核会对管道操作进行同步与互斥。 - 管道是半双工的，数据只能向一个方向流动；需要双方通信时，需要建立起两个管道 - 管道大小为65536 byte 如果不关闭读写端而采用分时的形式去读写也可以完成，因为半双工的意识是能双向传递但是不能同时 ```c #include "kernel/types.h" #include "kernel/stat.h" #include "user/user.h" int main(int argc, char **argv) { //no use args if(argc!=1) { fprintf(2, "usage: args is error\n"); exit(1); } int fd[2]; //fd[0] --read fd[1] --write if(pipe(fd)!=0) { fprintf(2, "usage: create pipe faild!\n"); exit(1); } int pid=fork(); if(pid<0) //创建失败 { fprintf(2, "usage: create process faild!\n"); exit(1); } else if(pid==0) //子进程 { sleep(5); char buf[255]; char *msg="pong"; if(read(fd[0], buf, sizeof(buf))==-1) { fprintf(2, "%d: read faild!\n",getpid()); exit(1); } close(fd[0]); printf("%d: received ping\n",getpid()); if(write(fd[1], msg, strlen(msg))==-1) { fprintf(2, "%d: write faild!\n",getpid()); exit(1); } close(fd[1]); exit(0); } else //父进程 { char buf[255]; char *msg="ping"; if(write(fd[1], msg, strlen(msg))==-1) { fprintf(2, "%d: write faild!\n",getpid()); exit(1); } close(fd[1]); sleep(30); if(read(fd[0], buf, sizeof(buf))==-1) { fprintf(2, "%d: read faild!\n",getpid()); exit(1); } close(fd[0]); printf("%d: received pong\n",getpid()); exit(0); } exit(0); } ``` 评分 ```shell make GRADEFLAGS=pingpong grade make[1]: Leaving directory '/home/ubuntu/xv6-labs-2020' == Test pingpong == make GRADEFLAGS=pingpong gradepingpong: OK (6.2s) ``` primes ```c #include <unistd.h> int dup(int fd); //int dup(int fd) Return a new file descriptor referring to the same file as fd. int wait(int *status); //Wait for a child to exit; exit status in *status; returns child PID. ``` ```c #include "kernel/types.h" #include "user/user.h" #include "stddef.h" void primes(int readfd,int writefd) { int prenum,nextnum; if(read(readfd,&prenum,sizeof(int))) { printf("%d prime %d\n",getpid(),prenum); int pid=fork(); if(pid==0) { //**了 光想节省资源，使用一个管道 //这段代码会导致一边读一边写死循环的节奏！！！ while(read(readfd,&nextnum,sizeof(int))) { fprintf(2, "%d: read %d!\n",getpid(),nextnum); if(nextnum%prenum!=0) { if(write(writefd,&nextnum,sizeof(int))==-1) { fprintf(2, "%d: write faild!\n",getpid()); exit(1); } } } close(readfd); close(writefd); exit(0); } else if(pid>0) { wait(NULL); //printf("pid :%d write ok\n",getpid()); primes(readfd,writefd); } else { fprintf(2, "usage: fork is error\n"); exit(1); } } else { fprintf(2, "usage: read pipe is error\n"); exit(1); } } // 创建一个进程为主进程 创建一个子进程将2-35写入管道，然后递归判断 //先输出第一个元素，然后将n的倍数的元素写入另外一个管道递归执行直到为空 int main(int argc, char **argv) { int fd[2]; if(pipe(fd)!=0) //经过pipe函数后，fd存的是两个数，拿到这两个数就能对管道读写 { fprintf(2, "usage: create pipe is error\n"); exit(1); } int pid=fork(); if(pid==0) //子进程 { for(int i=2;i<36;i++) { write(fd[1],&i,sizeof(int));//guide说用数字比acsii码好使，然后xv6 book上是char *buf。所以对i取地址 } exit(0); } else if(pid>0) //父进程 { wait(NULL);//Wait for a child to exit; exit status in *status; returns child PID. //数据已经全部写入管道了 //guide上的意思应该是对管道复用否则系统资源不够分配 //当进程没有结束的时候管道应该是不会被释放的 fprintf(2, "pid %d: write ok!\n",getpid()); primes(fd[0],fd[1]); } else { fprintf(2, "usage: fork is error\n"); exit(1); } return 0; } ``` ```c #include "kernel/types.h" #include "user/user.h" #include "stddef.h" void primes(int readfd,int writefd) { int prenum,nextnum; if(read(readfd,&prenum,sizeof(int))) { if(prenum==-1) return; printf("prime %d\n",prenum); int pid=fork(); if(pid==0) { //**了 光想节省资源使用一个管道 //这段代码会导致一边读一边写死循环的节奏！！！ while(read(readfd,&nextnum,sizeof(int))) { if(nextnum==-1) break; if(nextnum%prenum!=0) { if(write(writefd,&nextnum,sizeof(int))==-1) { fprintf(2, "%d: write faild!\n",getpid()); exit(1); } } } int end_flag=-1; if(write(writefd,&end_flag,sizeof(int))) { fprintf(2, "usage: wirte pipe is error\n"); exit(1); } close(readfd); close(writefd); exit(0); } else if(pid>0) { wait(NULL); //printf("pid :%d write ok\n",getpid()); primes(readfd,writefd); } else { fprintf(2, "usage: fork is error\n"); exit(1); } } else { fprintf(2, "usage: read pipe is error\n"); exit(1); } return; } // 创建一个进程为主进程 创建一个子进程将2-35写入管道，然后递归判断 //先输出第一个元素，然后将n的倍数的元素写入另外一个管道递归执行直到为空 int main(int argc, char **argv) { int fd[2]; if(pipe(fd)!=0) //经过pipe函数后，fd存的是两个数，拿到这两个数就能对管道读写 { fprintf(2, "usage: create pipe is error\n"); exit(1); } int pid=fork(); if(pid==0) //子进程 { for(int i=2;i<36;i++) { //guide说用数字比acsii码好使，然后xv6 book上是char *buf。所以对i取地址 if(write(fd[1],&i,sizeof(int))==-1) { fprintf(2, "usage: wirte pipe is error\n"); exit(1); } } //标识符，因为只使用一个pipe需要区分一个那一次读写 int end_flag=-1; if(write(fd[1],&end_flag,sizeof(int))) { fprintf(2, "usage: wirte pipe is error\n"); exit(1); } exit(0); //执行完成结束占用 } else if(pid>0) //父进程 { wait(NULL);//Wait for a child to exit; exit status in *status; returns child PID. //数据已经全部写入管道了 //guide上的意思应该是对管道复用否则系统资源不够分配 //当进程没有结束的时候管道应该是不会被释放的 fprintf(2, "pid %d: write ok!\n",getpid()); primes(fd[0],fd[1]); exit(0); } else { fprintf(2, "usage: fork is error\n"); exit(1); } return 0; } ``` ```c make GRADEFLAGS=primes grade make[1]: Leaving directory '/home/ubuntu/xv6-labs-2020' == Test primes == primes: OK (3.2s) ``` 测试成功！调用primes的是主进程会一直存在，子进程完成读出-判断-写入后便会exit，调用primes的时候第一个元素就是素数。因为只使用一个管道，所以需要标识符来判断是不是本次primes的。然后文件表示符，说白了就是个int数字，跟id一样，所以当作参数传入。每次结束后需要exit结束占用，后边的进程才能正常读写。 ## find ([moderate](https://pdos.csail.mit.edu/6.828/2020/labs/guidance.html)) Write a simple version of the UNIX find program: find all the files in a directory tree with a specific name. Your solution should be in the file `user/find.c`. Some hints: - Look at user/ls.c to see how to read directories. - Use recursion to allow find to descend into sub-directories. - Don't recurse into "." and "..". - Changes to the file system persist across runs of qemu; to get a clean file system run make clean and then make qemu. - You'll need to use C strings. Have a look at K&R (the C book), for example Section 5.5. - Note that == does not compare strings like in Python. Use strcmp() instead. - Add the program to `UPROGS` in Makefile. Your solution is correct if produces the following output (when the file system contains the files `b` and `a/b`): ```shell $ make qemu ... init: starting sh $ echo > b $ mkdir a $ echo > a/b $ find . b ./b ./a/b $ ``` 先看ls.c的东西 ```c void ls(char *path) { char buf[512], *p; int fd; struct dirent de; struct stat st; if((fd = open(path, 0)) < 0){ //打开指定路径的文件/文件夹 fd文件描符 fprintf(2, "ls: cannot open %s\n", path); return; } /* #define T_DIR 1 // Directory #define T_FILE 2 // File #define T_DEVICE 3 // Device struct stat { int dev; // File system's disk device uint ino; // Inode number short type; // Type of file short nlink; // Number of links to file uint64 size; // Size of file in bytes }; */ if(fstat(fd, &st) < 0){ //根据文件描述符找到文件的描述状态 然后复制到st里面 fprintf(2, "ls: cannot stat %s\n", path); close(fd); return; } switch(st.type){ //根据文件是dir file 还是device做出分类 如果是文件夹则打印然后退出l case T_FILE: printf("%s %d %d %l\n", fmtname(path), st.type, st.ino, st.size); break; case T_DIR: if(strlen(path) + 1 + DIRSIZ + 1 > sizeof buf){ printf("ls: path too long\n"); break; }//文件超出缓冲区则不打印 strcpy(buf, path); //path复制到buf里面 p = buf+strlen(buf);//p指向字符串末尾在buf的位置 *p++ = '/';//附加一个“/”符号 while(read(fd, &de, sizeof(de)) == sizeof(de)){ //这个地方不太明白为什么是sizeof(de)==sizeof(de) 个人感觉sizeof(de)就好了 if(de.inum == 0) continue; memmove(p, de.name, DIRSIZ); p[DIRSIZ] = 0; if(stat(buf, &st) < 0){ printf("ls: cannot stat %s\n", buf); continue; } printf("%s %d %d %d\n", fmtname(buf), st.type, st.ino, st.size); } break; } close(fd); } // Directory is a file containing a sequence of dirent structures. #define DIRSIZ 14 struct dirent { ushort inum; char name[DIRSIZ]; }; ``` ```shell usertrap(): unexpected scause 0x000000000000000d pid=7 sepc=0x0000000000000110 stval=0x0000000000003008 ``` 如果遇到上述错误，应该是函数退出时应该使用exit(0)让操作系统知道命令结束而不是单纯return
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