文件系统：目录与文件
This commit is contained in:
lzy
@@ -162,6 +162,7 @@ int setvbuf(FILE *stream, char *buf, int mode, size_t size);
|
||||
*
|
||||
* !!! 里面有 malloc 动作，未释放
|
||||
* !!! 是方言，可以自己封装一个mygetline和mygetline_free
|
||||
* !!! 但是根据chatgpt，好像直接 free(*lineptr) 就行了
|
||||
*
|
||||
*/
|
||||
ssize_t getline(char **lineptr, size_t *n, FILE *stream);
|
||||
@@ -260,6 +261,77 @@ off_t lseek(int fd, offt offset, int whence);
|
||||
### IO的效率问题
|
||||
习题：将`mycpy.c`程序进行更改，将`BUFSIZE`的值放大，观察进程消耗的时间，注意性能出现拐点的值以及程序何时段错误。
|
||||
|
||||
解答：
|
||||
将`BUFSIZE`作为命令行参数传入，`int bufsize = atoi(argv[3]);`
|
||||
通过脚本进行试验：
|
||||
```bash
|
||||
#!/bin/bash
|
||||
|
||||
# 生成一个 5GB 的文件
|
||||
dd if=/dev/urandom of=/tmp/bigfile bs=1G count=5
|
||||
|
||||
# 输入和输出文件的路径
|
||||
src="/tmp/bigfile"
|
||||
dst="/tmp/outfile"
|
||||
|
||||
# 编译你的程序
|
||||
gcc -o mycpy_bufsize mycpy_bufsize.c
|
||||
|
||||
# 初始化 BUFSIZE
|
||||
bufsize=512
|
||||
|
||||
# 循环，每次 BUFSIZE * 2
|
||||
while true; do
|
||||
# 用 time 命令运行你的程序，并将结果重定向到一个临时文件
|
||||
{ time ./mycpy_bufsize $src $dst $bufsize; } 2> time.txt
|
||||
|
||||
# 检查程序的退出状态
|
||||
if [ $? -ne 0 ]; then
|
||||
echo "Max BUFSIZE before segfault: $bufsize"
|
||||
break
|
||||
fi
|
||||
|
||||
# 提取 time 的结果
|
||||
real_time=$(grep real time.txt | awk -F' ' '{print $2}')
|
||||
user_time=$(grep user time.txt | awk -F' ' '{print $2}')
|
||||
sys_time=$(grep sys time.txt | awk -F' ' '{print $2}')
|
||||
|
||||
# 输出 BUFSIZE 和 time 的结果
|
||||
echo "BUFSIZE: $bufsize, Real Time: $real_time, User Time: $user_time, Sys Time: $sys_time"
|
||||
|
||||
# BUFSIZE * 2
|
||||
bufsize=$((bufsize * 2))
|
||||
done
|
||||
|
||||
# 删除临时文件
|
||||
rm time.txt
|
||||
rm $src
|
||||
rm $dst
|
||||
|
||||
```
|
||||
|
||||
结果：
|
||||
```bash
|
||||
wan@SK-20240106UQUX:~/Linux-C-Notes/C13-Linux系统编程/io/sys$ ./time.sh
|
||||
BUFSIZE: 512, Real Time: 0m7.672s, User Time: 0m0.650s, Sys Time: 0m7.007s
|
||||
BUFSIZE: 1024, Real Time: 0m5.026s, User Time: 0m0.201s, Sys Time: 0m4.651s
|
||||
BUFSIZE: 2048, Real Time: 0m3.535s, User Time: 0m0.158s, Sys Time: 0m3.183s
|
||||
BUFSIZE: 4096, Real Time: 0m2.418s, User Time: 0m0.059s, Sys Time: 0m2.232s
|
||||
BUFSIZE: 8192, Real Time: 0m2.363s, User Time: 0m0.040s, Sys Time: 0m2.150s
|
||||
BUFSIZE: 16384, Real Time: 0m2.279s, User Time: 0m0.030s, Sys Time: 0m2.079s
|
||||
BUFSIZE: 32768, Real Time: 0m2.238s, User Time: 0m0.020s, Sys Time: 0m2.026s
|
||||
BUFSIZE: 65536, Real Time: 0m2.114s, User Time: 0m0.000s, Sys Time: 0m1.972s
|
||||
BUFSIZE: 131072, Real Time: 0m2.302s, User Time: 0m0.019s, Sys Time: 0m1.982s
|
||||
BUFSIZE: 262144, Real Time: 0m2.244s, User Time: 0m0.000s, Sys Time: 0m2.016s
|
||||
BUFSIZE: 524288, Real Time: 0m2.254s, User Time: 0m0.000s, Sys Time: 0m2.039s
|
||||
BUFSIZE: 1048576, Real Time: 0m2.249s, User Time: 0m0.010s, Sys Time: 0m2.037s
|
||||
BUFSIZE: 2097152, Real Time: 0m2.304s, User Time: 0m0.000s, Sys Time: 0m2.108s
|
||||
BUFSIZE: 4194304, Real Time: 0m2.234s, User Time: 0m0.010s, Sys Time: 0m2.082s
|
||||
Max BUFSIZE before segfault: 8388608
|
||||
```
|
||||
在`ulimit -a`中，我的系统的`stack size`是`8192`，所以`BUFSIZE`不能超过`8192`，否则会段错误。与测试结果一致。
|
||||
|
||||
|
||||
### 文件共享
|
||||
多个任务共同操作一个文件或者协同完成任务
|
||||
|
||||
@@ -325,3 +397,262 @@ int ioctl(int fd, unsigned long request, ... /* arg */);
|
||||
|
||||
### /dev/fd/目录
|
||||
**虚目录**：显示当前进程的文件描述符信息
|
||||
|
||||
|
||||
|
||||
# 文件系统
|
||||
|
||||
类`ls`的实现，如`myls -l -a -i -n`
|
||||
|
||||
`cmd --长格式 -短格式 非选项的传参`
|
||||
|
||||
## 目录和文件
|
||||
|
||||
1. 获取文件属性
|
||||
```c
|
||||
/**
|
||||
* 将文件的属性存储到buf中
|
||||
* stat : 通过文件路径获取属性，面对符号链接文件时，
|
||||
* 获取的是指向的目标文件的属性
|
||||
* fstat: 通过文件描述符获取属性
|
||||
* lstat: 通过文件路径获取属性，面对符号链接文件时，
|
||||
*/
|
||||
int stat(const char *path, struct stat *buf);
|
||||
int fstat(int fd, struct stat *buf);
|
||||
int lstat(const char *path, struct stat *buf);
|
||||
|
||||
struct stat {
|
||||
dev_t st_dev; /* ID of device containing file */
|
||||
ino_t st_ino; /* inode number */
|
||||
// 文件唯一标识，身份证号
|
||||
|
||||
mode_t st_mode; /* protection */
|
||||
// st_mode: 文件权限+文件类型
|
||||
// 文件权限
|
||||
// 七种文件类型：dcb-lsp
|
||||
|
||||
nlink_t st_nlink; /* number of hard links */
|
||||
uid_t st_uid; /* user ID of owner */
|
||||
gid_t st_gid; /* group ID of owner */
|
||||
dev_t st_rdev; /* device ID (if special file) */
|
||||
off_t st_size; /* total size, in bytes */
|
||||
// 在linux下，与windows不同，size值仅仅是属性
|
||||
// 不能实际体现占用磁盘大小，详见 big.c
|
||||
|
||||
blksize_t st_blksize; /* blocksize for file system I/O */
|
||||
blkcnt_t st_blocks; /* number of 512B blocks allocated */
|
||||
time_t st_atime; /* time of last access */
|
||||
time_t st_mtime; /* time of last modification */
|
||||
time_t st_ctime; /* time of last status change */
|
||||
};
|
||||
```
|
||||
|
||||
2. 文件访问权限
|
||||
`st_mode`是一个16位的二进制数，文件类型，文件权限，特殊权限。
|
||||
|
||||
3. `umask`
|
||||
作用：防止产生权限过松的文件。
|
||||
`0666 &~umask`
|
||||
`umask`也是一个终端命令，可以查看和设置。
|
||||
`mode_t umask(mode_t mask);`
|
||||
|
||||
4. 文件权限的更改/管理
|
||||
```c
|
||||
/**
|
||||
* 更改文件权限
|
||||
*/
|
||||
int chmod(const char *path, mode_t mode);
|
||||
int fchmod(int fd, mode_t mode);
|
||||
```
|
||||
|
||||
5. 粘住位
|
||||
t位，例如`/tmp`目录。
|
||||
|
||||
6. 文件系统：`FAT`, `UFS`
|
||||
文件或数据的存储格式。
|
||||
- `FAT`：静态存储的单链表
|
||||
```c
|
||||
struct node_st{
|
||||
int next[N];
|
||||
char data[N][SIZE];
|
||||
};
|
||||
```
|
||||
- `UFS`：
|
||||
缺点：不善于处理大量的小文件，因为每个文件都有一个`inode`，占用空间。
|
||||
|
||||
> 面试题：
|
||||
> 不用比较，比较两个uint32_t的大小
|
||||
> 使用位图
|
||||
|
||||
7. 硬链接，符号链接
|
||||
- 硬链接
|
||||
`ln bigfile bigfile_link`
|
||||
与目录项是同义词
|
||||
相当于目录项又弄了一份，使用`ls -i`可以看到`inode`号相同。
|
||||
|
||||
限制：不能给分区建立，不能给目录建立
|
||||
|
||||
- 符号链接
|
||||
`ln -s bigfile_link bigfile_s`
|
||||
|
||||
优点：可以跨分区，可以给目录建立
|
||||
|
||||
```c
|
||||
int link(const char *oldpath, const char *newpath);
|
||||
|
||||
/**
|
||||
* 只有没有引用的数据才会真正删除
|
||||
* 可以利用这一点创建匿名文件
|
||||
*/
|
||||
int unlink(const char *pathname);
|
||||
|
||||
int remove(const char *pathname);
|
||||
|
||||
/**
|
||||
* 改变文件的路径或者名字
|
||||
*/
|
||||
int rename(const char *oldpath, const char *newpath);
|
||||
```
|
||||
|
||||
8. `utime`
|
||||
```c
|
||||
/**
|
||||
* 更改文件最后读/写的时间
|
||||
*/
|
||||
int utime(const char *filename, const struct utimbuf *times);
|
||||
|
||||
struct utimbuf {
|
||||
time_t actime; /* access time */
|
||||
time_t modtime; /* modification time */
|
||||
};
|
||||
|
||||
struct time_t {
|
||||
long tv_sec; /* seconds */
|
||||
long tv_usec; /* microseconds */
|
||||
};
|
||||
```
|
||||
|
||||
9. 目录的创建和销毁
|
||||
`mkdir, rmdir`
|
||||
```c
|
||||
int mkdir(const char *pathname, mode_t mode);
|
||||
|
||||
/**
|
||||
* 只有目录为空才能删除
|
||||
*/
|
||||
int rmdir(const char *pathname);
|
||||
```
|
||||
|
||||
10. 更改当前工作路径
|
||||
`cd, pwd`
|
||||
```c
|
||||
/**
|
||||
* 改变当前工作路径
|
||||
* 可以突破假根目录
|
||||
* 但是不能突破chroot
|
||||
*/
|
||||
int chdir(const char *path);
|
||||
int fchdir(int fd);
|
||||
|
||||
/**
|
||||
* 获取当前工作路径
|
||||
*/
|
||||
long getcwd(char *buf, unsigned long size);
|
||||
```
|
||||
|
||||
11. 分析目录/读取目录内容
|
||||
|
||||
```c
|
||||
|
||||
/**
|
||||
* 法一
|
||||
* 解析模式/通配符
|
||||
*
|
||||
* @prarm: pattern 匹配模式
|
||||
* @prarm: flags 匹配标志
|
||||
* @prarm: errfunc 错误回调函数
|
||||
* @prarm: pglob 匹配结果
|
||||
*
|
||||
* @return 匹配的文件数量
|
||||
*/
|
||||
int glob(const char *restrict pattern, int flags,
|
||||
int (*errfunc)(const char *epath, int eerrno),
|
||||
glob_t *restrict pglob);
|
||||
/**
|
||||
* 释放glob_t结构体
|
||||
*/
|
||||
void globfree(glob_t *pglob);
|
||||
|
||||
/**
|
||||
* 与argc, argv类似
|
||||
*/
|
||||
typedef struct {
|
||||
size_t gl_pathc; /* Count of paths matched so far */
|
||||
char **gl_pathv; /* List of matched pathnames */
|
||||
size_t gl_offs; /* Slots to reserve in gl_pathv */
|
||||
} glob_t;
|
||||
|
||||
/**
|
||||
* 法二
|
||||
*/
|
||||
|
||||
/**
|
||||
* 打开一个目录
|
||||
* 返回一个指向DIR结构体的指针
|
||||
* 是堆区，需要 closedir 释放
|
||||
*/
|
||||
DIR *opendir(const char *name);
|
||||
DIR *fdopendir(int fd);
|
||||
|
||||
/**
|
||||
* 关闭一个目录
|
||||
*/
|
||||
int closedir(DIR *dirp);
|
||||
|
||||
/**
|
||||
* 读取一个目录
|
||||
*
|
||||
* 返回指针指向静态区
|
||||
*/
|
||||
struct dirent *readdir(DIR *dirp);
|
||||
int readdir_r(DIR *restrict dirp,
|
||||
struct dirent *restrict entry,
|
||||
struct dirent **restrict result);
|
||||
|
||||
struct dirent {
|
||||
ino_t d_ino; /* inode number */
|
||||
off_t d_off; /* offset to the next dirent */
|
||||
unsigned short d_reclen; /* length of this record */
|
||||
unsigned char d_type; /* type of file; not supported
|
||||
by all file system types */
|
||||
char d_name[256]; /* filename */
|
||||
};
|
||||
|
||||
|
||||
/**
|
||||
* 重置一个目录
|
||||
*/
|
||||
void rewinddir(DIR *dirp);
|
||||
|
||||
void seekdir(DIR *dirp, long offset);
|
||||
|
||||
long telldir(DIR *dirp);
|
||||
|
||||
/**
|
||||
* du 命令
|
||||
* 以字节为单位，统计目录下所有文件的大小
|
||||
*
|
||||
*/
|
||||
|
||||
|
||||
```
|
||||
|
||||
作业：用另一套函数实现`mydu`
|
||||
|
||||
|
||||
## 系统数据文件和信息
|
||||
|
||||
|
||||
|
||||
## 进程环境
|
||||
|
||||
|
||||
Reference in New Issue
Block a user