One of the prominent reasons to use direct IO, is for it's ability to do actual direct IO, bypassing the operating system cache and getting the data from the disk directly.
The flag to do that (O_DIRECT) is missing from the documentation above. Maybe for good reasons, because this type of IO only works on blockdevices, not on files, and should only be used if you are **really** sure what you are doing.
dio_open
(PHP 4 >= 4.2.0, PHP 5 < 5.1.0)
dio_open — 在 C 库输入/输出流函数允许的更低级别打开（必要时创建）文件
参数
-
filename -
要打开的文件路径。
-
flags -
flags参数是按位或运算值，包含以下列表的标志。 必须包含O_RDONLY、O_WRONLY或O_RDWR中的一个。此外，可以包含此列表中其它标志的任意组合。-
O_RDONLY- 打开文件读访问。 -
O_WRONLY- 打开文件写访问。 -
O_RDWR- 打开文件读写。 -
O_CREAT- 如果文件不存在，创建文件。 -
O_EXCL- 如果同时设置了O_CREAT和O_EXCL，并且文件已存在，dio_open() 将执行失败。 -
O_TRUNC- 如果文件存在且已打开写访问，将会被截断到 0 长度。 -
O_APPEND- 写操作在文件末尾写数据。 -
O_NONBLOCK- 设置非阻塞模式。 -
O_NOCTTY- 防止操作系统在打开 TTY 设备文件时将文件指定为进程的控制终端。
-
-
mode -
如果
flags包含O_CREAT，mode将设置文件权限（创建权限）。当flags指定了O_CREAT标志时，需要mode才能正确操作，否则将会被忽略。分配给创建文件的实际权限照例受到进程的 umask 设置的影响。
返回值
文件描述符，错误时是 false。
示例
示例 #1 打开文件描述符
<?php
$fd = dio_open('/dev/ttyS0', O_RDWR | O_NOCTTY | O_NONBLOCK);
dio_close($fd);
?>
add a note
User Contributed Notes 4 notes
Marius Karthaus ¶
14 years ago
j at pureftpd dot org ¶
19 years ago
Please note that dio_open()/dio_write()/dio_close() is *faster* than fopen()/fwrite()/fclose() for files.
fwrite() has to manage a 8k buffer, while dio_write() just issue a single write(). The end result is less system calls and less memory access.
Also, giving the full size to write() as with dio_write() let filesystems properly use preallocation in order to avoid fragmentation.
Anonymous ¶
12 years ago
"The prominent reason" to use direct I/O is when your application provides its own cache feature, so you won't do double caching
alla at cyber dot com dot au ¶
21 years ago
To specify a combination of flags you OR them together.
This was the only way I could get it to append:
$fd = dio_open($file, O_WRONLY | O_APPEND);
