1. Computers
  2. Display Drivers
  3. Graphics Cards
  4. Memory
  5. Motherboards
  6. Processors
  7. Software
  8. Storage
  9. Operating Systems


Facebook RSS Twitter Twitter Google Plus


Phoronix Test Suite

OpenBenchmarking Benchmarking Platform
Phoromatic Test Orchestration

OverlayFS File-System Proposed For Linux 3.10 Kernel

Linux Kernel

Published on 13 March 2013 08:32 PM EDT
Written by Michael Larabel in Linux Kernel
7 Comments

The Overlay File-System has been in development for several years and is used by some notable Linux distributions, but has yet to be merged into the mainline Linux kernel after having to be pulled a few times in the past. The new plan is to merge OverlayFS for the Linux 3.10 kernel.

With the patches now up to their sixteenth revision, Miklos Szeredi has called upon Linus Torvalds and Al Viro (the VFS maintainer) to consider pulling OverlayFS for inclusion into the Linux 3.10 release.

Szeredi writes in his latest plea with the Linux kernel developers, "It's included in Ubuntu and openSUSE, used by OpenWrt and various other projects. I regularly get emails asking when it will be included in mainline."

Introducing the new Linux file-system is made-up of thirteen patches and the v16 revision to them can be found on the kernel mailing list.

As far as the Overlay File-System approach to a union file-system, the kernel documentation describes itself:
This document describes a prototype for a new approach to providing overlay-filesystem functionality in Linux (sometimes referred to as union-filesystems). An overlay-filesystem tries to present a filesystem which is the result over overlaying one filesystem on top of the other.

The result will inevitably fail to look exactly like a normal filesystem for various technical reasons. The expectation is that many use cases will be able to ignore these differences.

This approach is 'hybrid' because the objects that appear in the filesystem do not all appear to belong to that filesystem. In many cases an object accessed in the union will be indistinguishable from accessing the corresponding object from the original filesystem. This is most obvious from the 'st_dev' field returned by stat(2).

While directories will report an st_dev from the overlay-filesystem, all non-directory objects will report an st_dev from the lower or upper filesystem that is providing the object. Similarly st_ino will only be unique when combined with st_dev, and both of these can change over the lifetime of a non-directory object. Many applications and tools ignore these values and will not be affected.
Linus Torvalds looks like he may finally pull the file-system for Linux 3.10. He already responded to the thread:
Yes, I think we should just do it. It's in use, it's pretty small, and the other alternatives are worse. Let's just plan on getting this thing done with.

Al, I realize you may not love this, but can you please give this alook? People clearly want to use it. In particular the new interfaces, like the inode ops open function with dentry passed in or whatever? The changes outside of overlayfs looked fine to me.
Al's response at the moment is, "I'll post a review tonight or tomorrow. FWIW, I was not too happy with it the last time I looked, but I'll obviously need to reread the whole thing."

About The Author
Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via and or contacted via .
Latest Articles & Reviews
  1. Ubuntu 15.04 Offers Faster OpenGL For AMD Radeon GPUs On Open-Source
  2. Ubuntu 15.04 Brings Some Graphics Performance Improvements For Intel Haswell
  3. Sub-$20 802.11n USB WiFi Adapter That's Linux Friendly
  4. The Lenovo T450s Is Working Beautifully With Linux
  5. Linux 4.0 SSD EXT4 / Btrfs / XFS / F2FS Benchmarks
  6. Linux 4.0 Hard Drive Comparison With Six File-Systems
Latest Linux News
  1. Phoronix Server Migration
  2. GCC 5.2 Will Come In Two To Three Months
  3. AMD FP3 Motherboard Ported To Coreboot
  4. The Difference In Optimizations Between NIR & GLSL
  5. OpenMandriva Lx 3 Alpha: Adds UEFI Support, Defaults To LXQt
  6. Systemd Kills Off Shutdownd
  7. There's Now More Than 1,100 Games On Steam For Linux
  8. Btrfs In Linux 4.1 Has Fixes For File-Systems Of 20 Terabytes & Up
  9. Microsoft's CoreCLR Now Works On FreeBSD
  10. Unigine 2.0 Beta 2 Brings PBR, SSR, Kinect 2 Support
Most Viewed News This Week
  1. AMD Releases New "AMDGPU" Linux Kernel Driver & Mesa Support
  2. Ubuntu's Desktop-Next Switching From .DEBs To Snappy
  3. My Favorite Computer Desk Of The Past Decade For Less Than $100
  4. AMD Open-Sources "Addrlib" From Catalyst
  5. Library Operating System (LibOS) For Linux Still Being Pursued
  6. Debian 8.0 Jessie Is Ready For Release This Weekend
  7. GIMP's Porting To GTK3 Continues
  8. Features Thus Far For The Linux 4.1 Kernel