Linux 文件与目录

文件描述符

空洞程序示例：
[root@benxintuzi IO]# cat hole.c
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>

char buf1[] = "benxintuzi";
char buf2[] = "BENXINTUZI";

int main(void)
{
int fd;

if ((fd = open("file", O_RDWR | O_CREAT)) == -1)
printf("create error\n");

if (write(fd, buf1, 10) != 10)
printf("buf1 write error\n");
/* offset now = 10 */

if (lseek(fd, 16384, SEEK_SET) == -1)
printf("lseek error\n");
/* offset now = 16384 */

if (write(fd, buf2, 10) != 10)
printf("buf2 write error\n");
/* offset now = 16394 */

return 0;
}

[root@benxintuzi IO]# ls -l file
--wsr-S---. 1 root root 16394 Aug 25 02:13 file
[root@benxintuzi IO]# od -c file
0000000   b   e   n   x   i   n   t   u   z   i  \0  \0  \0  \0  \0  \0
0000020  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0040000   B   E   N   X   I   N   T   U   Z   I
0040012

#include <stdio.h>
#include <unistd.h>

#define BUFFSIZE 4096

int main(void)
{
int     n;
char    buf[BUFFSIZE];

while((n = read(STDIN_FILENO, buf, BUFFSIZE)) > 0)
if(write(STDOUT_FILENO, buf, n) != n)
printf("write error\n");

if(n < 0)
printf("read error\n");

return 0;
}

[root@benxintuzi IO]# ./read
benxintuzi
benxintuzi
hello
hello
tuzi
tuzi
^C
[root@benxintuzi IO]#

文件共享

#include <unistd.h> int dup(int fd); int dup2(int fd, int fd2); 函数返回新的文件描述符，与fd共享同一个文件表项。 说明： 由dup返回的文件描述符一定是当前可用的最小的文件描述符。对于dup2，可以用fd2指定特定的新的文件描述符。如果fd2已经打开，则先将其关闭；如果fd == fd2，则不关闭而直接返回。

Unix文件类型

[root@benxintuzi IO]# cat types.c
#include <sys/stat.h>
#include <stdio.h>

int main(int argc, char** argv)
{
int i;
struct stat buf;
char* ptr;

for(i = 1; i < argc; i++)
{
printf("%s: ", argv[i]);
if(lstat(argv[i], &buf) < 0)
{
printf("lstat error\n");
continue;
}
if(S_ISREG(buf.st_mode))
ptr = "regular";
else if(S_ISDIR(buf.st_mode))
ptr = "directory";
else if(S_ISBLK(buf.st_mode))
ptr = "block special";
else if(S_ISCHR(buf.st_mode))
ptr = "character special";
else if(S_ISFIFO(buf.st_mode))
ptr = "fifo";
else if(S_ISLNK(buf.st_mode))
ptr = "symbolic link";
else if(S_ISSOCK(buf.st_mode))
ptr = "socket";
else
ptr = "unknown mode";
printf("%s\n", ptr);
}

return 0;
}

[root@benxintuzi IO]# gcc types.c -o types
[root@benxintuzi IO]# ./types /etc/passwd /etc /dev/tty /dev/cdrom
/etc/passwd: regular
/etc: directory
/dev/tty: character special
/dev/cdrom: symbolic link

文件访问权限

[root@benxintuzi IO]# cat access.c
#include <fcntl.h>
#include <stdio.h>

int main(int argc, char** argv)
{
if(argc != 2)
{
printf("usage: execfile <pathname>\n");
return 1;
}
if(access(argv[1], R_OK) < 0)
printf("access error for %s\n", argv[1]);
else
printf("read access OK\n");

return 0;
}

[root@benxintuzi IO]# gcc access.c -o access
[root@benxintuzi IO]# ./access
usage: execfile <pathname>
[root@benxintuzi IO]# ./access types.c
read access OK
[root@benxintuzi IO]# ./access types
read access OK
[root@benxintuzi IO]# ./access /
read access OK

#include <fcntl.h>
#include <stdio.h>

#define RWRWRW (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH)

int main(void)
{
umask(0);     # 开放全部权限
if(creat("foo", RWRWRW) < 0)
printf("create error for foo\n");

umask(S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);    # 关闭组和其他用户的访问权限
if(creat("bar", RWRWRW) < 0)
printf("create error for bar\n");

return 0;
}

[root@benxintuzi IO]# ./umask
[root@benxintuzi IO]# ls -l foo bar
-rw-------. 1 root root 0 Aug 25 21:57 bar
-rw-rw-rw-. 1 root root 0 Aug 25 21:57 foo

[root@benxintuzi IO]# cat chmod.c
#include <sys/stat.h>
#include <stdio.h>

int main(void)
{
struct stat statbuf;

/* turn on set-group-ID and turn off group-execute */
if(stat("foo", &statbuf) < 0)
printf("stat error for foo\n");
if(chmod("foo", (statbuf.st_mode & ~S_IXGRP) | S_ISGID) < 0)
printf("chmod error for foo");

/* set absolute mode to "rw-r--r--" */
if(chmod("bar", S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) < 0)
printf("chmod error for bar");

return 0;
}

[root@benxintuzi IO]# gcc chmod.c -o chmod
[root@benxintuzi IO]# ./chmod
[root@benxintuzi IO]# ls -l foo bar
-rw-r--r--. 1 root root 0 Aug 25 21:57 bar
-rw-rwSrw-. 1 root root 0 Aug 25 21:57 foo

文件系统

符号链接

关于时间

关于目录

设备特殊文件

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>

int main(int argc, char** argv)
{
int i;
struct stat buf;
for(i = 1; i < argc; i++)
{
printf("%s: ", argv[i]);
if(stat(argv[i], &buf) < 0)
{
printf("stat error\n");
continue;
}
printf("dev = %d/%d    ", major(buf.st_dev), minor(buf.st_dev));
if(S_ISCHR(buf.st_mode) || S_ISBLK(buf.st_mode))
{
printf("rdev = %d/%d", major(buf.st_rdev), minor(buf.st_rdev));
}
printf("\n");
}

return 0;
}

[root@benxintuzi IO]# ./dev / /home /dev/tty[01]
/: dev = 8/2
/home: dev = 8/2
/dev/tty0: dev = 0/5    rdev = 4/0
/dev/tty1: dev = 0/5    rdev = 4/1