1. IO system call

six basic operation:

open

create

close

write

read

lseek

ioctl

unlink

更高级的IO system call:

pread

pwrite

readv

writev

preadv （calls combine the effects of lseek() and read() (or write()) into a single system call.）

pwritev

aio_read

aio_write

lio_listio

unlink

flush

dup2

2.  文件中data和meta-data的cache属性：

O_SYNC: write operation returns only when both data and meta data stored on physical disk

O_DSYNC: write operation   returns only when data  stored on physical disk

O_RSYNC: read operation returns before time-stamp updated

O_DIRECT: return only when data submitted to disk driver's IO queue (?)

3. memory mapped files

根本功能是：把一个文件映射到当前进程的用户空间

4. stdio file operation

重点是理解下面的数据结构，他说unistd.h file IO 和stdlib.h中file io的接口：

struct _IO_FILE {

char *_IO_read_ptr;

/*

Current read pointer */

char *_IO_read_end;

/*

End of get area. */

char *_IO_read_base;

/*

Start of putback and get area. */

char *_IO_write_base;

/*

Start of put area. */

char *_IO_write_ptr;

/*

Current put pointer. */

char *_IO_write_end;

/*

End of put area. */

char *_IO_buf_base;

/*

Start of reserve area. */

char *_IO_buf_end;

/*

End of reserve area. */

int

int

_blksize;

_fileno;

};

typedef struct _IO_FILE FILE;

学习并了解到的新的函数：

setbuf();

setvbuf()；

setbuffer();

setvbuf()；

文中还提供了经典的例子，来对比和分析NON buffer/Line buffer/File buffer对性能的不同影响。 还有一个重要的思想就是：如果对性能要求很高，需要尽可能地bypass std io library。