c - 在C mmap文件中写入: Permission denied. Linux

Question

这是我的代码:

   #include <stdio.h>
   #include <stdlib.h>
   #include <fcntl.h>
   #include <sys/types.h>
   #include <sys/stat.h>
   #include <sys/mman.h>

   int main()
   {
    int fd=open("/home/victor/hello",O_WRONLY);

    if(fd<0)
    {
            perror("Open");
            exit(EXIT_FAILURE);
    }

    struct stat sbuf;

    if(fstat(fd, &sbuf)==-1){
            perror("stat");
            close(fd);
            exit(EXIT_FAILURE);
    }

    void* file_memory= mmap(NULL, sbuf.st_size, PROT_WRITE, MAP_SHARED,fd,0);
    if (file_memory == MAP_FAILED ) {
            perror("Error mmapping the file");
            close(fd);
            exit(EXIT_FAILURE);
    }

    return 0;
   }

我也尝试过这个

    int fd=open("/home/victor/hello",O_WRONLY|0777);

但这是同样的错误:

映射文件时出错:权限被拒绝

执行 ls -l |格列普霍拉 -rwxrwxrwx 1 维克多 维克多 24 十月 24 01:47 你好

出了什么问题？

Answer 1

来自 glibc 手册，正如上面的 R.. 和 Iwillnotexist Idonotexist 已经指出的:

Note that most hardware designs cannot support write permission without read permission, and many do not distinguish read and execute permission. Thus, you may receive wider permissions than you ask for, and mappings of write-only files may be denied even if you do not use PROT_READ.

http://www.gnu.org/software/libc/manual/html_node/Memory_002dmapped-I_002fO.html