玥世界

Chapter 2 File I/O

1. the kernel maintains a per-process list of open files, called the file table
     i. index: nonnegative int "file descriptors"
        a. file descriptors is int type
        b. by default, the maximum is 1024, but it can be configured as high as 1,048,576 (2^20)
        c. by convention:
            * stdin: fd = 0 (STDIN_FILENO)
            * stdout: fd = 1 (STDOUT_FILENO)
            * stderr: fd = 2 (STDERR_FILENO)
     ii. a pointer to an in-memory copy of the file's backing inode(?) and associated metadata
2. by default, a child process receives a copy of its parent's file table (but the change will not effect the parent)
3. open files
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    int open (const char* filename, int flags[, mode_t mode]);
    return: file descriptor if success, -1 if error
    flags: O_RDONLY, O_WRONLY, or O_RDWR, etc.  // the access right of the open file