directio

README

DirectIO

This is library for the Go language to enable use of Direct IO under all supported OSes of Go.

Direct IO does IO to and from disk without buffering data in the OS. It is useful when you are reading or writing lots of data you don't want to fill the OS cache up with.

See here for package docs

http://go.pkgdoc.org/github.com/ncw/directio

Install

Directio is a Go library and installs in the usual way

go get github.com/ncw/directio

Usage

Instead of using os.OpenFile use directio.OpenFile

in, err := directio.OpenFile(file, os.O_RDONLY, 0666)

And when reading or writing blocks, make sure you do them in chunks of directio.BlockSize using memory allocated by directio.AlignedBlock

block := directio.AlignedBlock(BlockSize)
    _, err := io.ReadFull(in, block)

License

This is free software under the terms of MIT the license (check the COPYING file included in this package).

Contact and support

The project website is at:

• https://github.com/ncw/directio

There you can file bug reports, ask for help or contribute patches.

Authors

• Nick Craig-Wood nick@craig-wood.com

Contributors

• Your name goes here!

Documentation

Overview

This is library for the Go language to enable use of Direct IO under all supported OSes of Go.

Direct IO does IO to and from disk without buffering data in the OS. It is useful when you are reading or writing lots of data you don't want to fill the OS cache up with.

Instead of using os.OpenFile use directio.OpenFile

in, err := directio.OpenFile(file, os.O_RDONLY, 0666)

And when reading or writing blocks, make sure you do them in chunks of directio.BlockSize using memory allocated by directio.AlignedBlock

	block := directio.AlignedBlock(BlockSize)
        _, err := io.ReadFull(in, block)

Index

• Constants
• func AlignedBlock(BlockSize int) []byte
• func OpenFile(path string, mode int, perm os.FileMode) (file *os.File, err error)

Constants

const (
	// Size to align the buffer to
	AlignSize = 4096

	// Minimum block size
	BlockSize = 4096

	// Extra flags for windows
	FILE_FLAG_NO_BUFFERING  = 0x20000000
	FILE_FLAG_WRITE_THROUGH = 0x80000000
)

Functions

func AlignedBlock

func AlignedBlock(BlockSize int) []byte

AlignedBlock returns []byte of size BlockSize aligned to a multiple of AlignSize in memory (must be power of two)

func OpenFile

func OpenFile(path string, mode int, perm os.FileMode) (file *os.File, err error)

OpenFile is a modified version of os.OpenFile which sets the passes the following flags to windows CreateFile.

The FILE_FLAG_NO_BUFFERING takes this concept one step further and eliminates all read-ahead file buffering and disk caching as well, so that all reads are guaranteed to come from the file and not from any system buffer or disk cache. When using FILE_FLAG_NO_BUFFERING, disk reads and writes must be done on sector boundaries, and buffer addresses must be aligned on disk sector boundaries in memory.

FIXME copied from go source then modified