Direct IO 函数
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dio_open

(PHP 4 >= 4.2.0, PHP 5 <= 5.0.5)

dio_open — Opens a file (creating it if necessary) at a lower level than the C library input/ouput stream functions allow.

说明

resource dio_open ( string $filename , int $flags [, int $mode = 0 ] )

dio_open() opens a file and returns a new file descriptor for it.

参数

filename

The pathname of the file to open.

flags

The flags parameter is a bitwise-ORed value comprising flags from the following list. This value must include one of O_RDONLY, O_WRONLY, or O_RDWR. Additionally, it may include any combination of the other flags from this list.

  • O_RDONLY - opens the file for read access.

  • O_WRONLY - opens the file for write access.

  • O_RDWR - opens the file for both reading and writing.

  • O_CREAT - creates the file, if it doesn't already exist.

  • O_EXCL - if both O_CREAT and O_EXCL are set and the file already exists, causes dio_open() to fail.

  • O_TRUNC - if the file exists and is opened for write access, the file will be truncated to zero length.

  • O_APPEND - write operations write data at the end of the file.

  • O_NONBLOCK - sets non blocking mode.

  • O_NOCTTY - prevent the OS from assigning the opened file as the process's controlling terminal when opening a TTY device file.

mode

If flags contains O_CREAT, mode will set the permissions of the file (creation permissions). Mode is required for correct operation when O_CREAT is specified in mode and is ignored otherwise.

The actual permissions assigned to the created file will be affected by the process's umask setting as per usual.

返回值

A file descriptor or FALSE on error.

范例

Example #1 Opening a file descriptor

<?php

$fd = dio_open('/dev/ttyS0', O_RDWR | O_NOCTTY | O_NONBLOCK);

dio_close($fd);
?>

参见

Direct IO 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: Opens a file (creating it if necessary) at a lower level than the C library input/ouput stream functions allow.

用户评论:

Anonymous (08-Apr-2012 10:12)

"The prominent reason" to use direct I/O is when your application provides its own cache feature, so you won't do double caching

Marius Karthaus (03-Mar-2010 08:02)

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.

j at pureftpd dot org (24-Jan-2005 12:13)

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.

alla at cyber dot com dot au (22-Mar-2003 03:16)

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);