"The prominent reason" to use direct I/O is when your application provides its own cache feature, so you won't do double caching
(PHP 4 >= 4.2.0, PHP 5 <= 5.0.5, PHP 7)
dio_open — Opens a file (creating it if necessary) at a lower level than the C library input/ouput stream functions allow.
$filename
, int $flags
[, int $mode = 0
] )dio_open() opens a file and returns a new file descriptor for it.
filenameThe 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, dio_open() will 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 flags and is ignored
otherwise.
The actual permissions assigned to the created file will be affected by the process's umask setting as per usual.
A file descriptor or FALSE on error.
Example #1 Opening a file descriptor
<?php
$fd = dio_open('/dev/ttyS0', O_RDWR | O_NOCTTY | O_NONBLOCK);
dio_close($fd);
?>
"The prominent reason" to use direct I/O is when your application provides its own cache feature, so you won't do double caching
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.
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.
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);