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https://github.com/github/libprojfs

Linux projected filesystem library
https://github.com/github/libprojfs

filesystems fuse-filesystem git vfsforgit

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Linux projected filesystem library

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README 

        
# libprojfs



A Linux projected filesystem library, similar in concept to the Windows

[Projected File System][winprojfs] and developed in conjunction with the

[VFSForGit][vfs4git] project.



While the libprojfs C library may also be used independently of VFSForGit,

our primary goal is to enable users to run the VFSForGit client

on a Linux system.



**PLEASE NOTE:**

At present libprojfs is undergoing rapid development and its design

and APIs may change significantly; some features are also incomplete,

and so we do not recommend libprojfs for any production environments.



However, we wanted to share our progress to date, and we hope others

are as excited as we are at the prospect of running the VFSForGit

client on Linux in the not-too-distant future!



## Current Status



| Branch     | Functional Tests                                          |

| :--------: | :-------------------------------------------------------: |

| **master** | [![CI status: master][ci-master-status]][ci-master-redir] |



The library is under active development and supports basic

directory projection, with additional features added regularly.



We will only make a first, official versioned release once initial

development is complete.



A libprojfs filesystem can currently be used to mount a VFSForGit

[`MirrorProvider`][vfs4git-mirror] test client; we expect to continue our

pre-release development until the VFSForGit client proper is also

functional with libprojfs, at which point we may make an initial

tagged release.



## Design



The libprojfs library is designed to function as a stackable Linux

filesystem supporting a "provider" process which implements custom

callbacks to populate files and directories on demand.  This is

illustrated in the context of a VFSForGit provider below:



![Illustration of libprojfs in provider context](docs/images/phase1.png)



Actual file storage is delegated to a "lower" storage filesystem,

which may be any Linux filesystem, e.g., ext4.  At the time

when a libprojfs filesystem mount is created, there may be no

files or directories in the lower filesystem yet.



As normal filesystem requests are made within the libprojfs mount

(e.g., by `ls` or `cat`), libprojfs intercepts the requests

and queries the provider process for the actual contents of the

file or directory.  The provider's response is then written to

the lower filesystem so future accesses may be satisfied without

querying the provider again.



See our [design document][design-linux] for more details.



We anticipate that whether libprojfs remains a [FUSE][fuse-man]-based

library, or becomes a [libfuse][libfuse]-like interface to a Linux kernel

module, it may be useful for purposes other than running a VFSForGit

client.



For this reason, we have tried to ensure that our native

[event notification API](include/projfs_notify.h)

is aligned closely with the Linux kernel's

[fanotify][fanotify]/[inotify][inotify]/[fsnotify][fsnotify] APIs.



## Getting Started



Please see our detailed [Build and Installation][build]

page for step-by-step instructions on how to build and install

libprojfs and its dependencies on Linux, and (optionally) also build and

run the VFSForGit `MirrorProvider` test utility with libprojfs.



So long as libprojfs remains based on [FUSE][fuse-man], the primary

dependency for libprojfs is the user-space [libfuse][libfuse] library,

as well as having the Linux [`fuse`][fuse-mod] kernel module installed.



Support for [`user.*` extended attributes][xattr] must also be enabled

on the "lower" storage filesystem.  Your Linux kernel should have

been compiled with the necessary configuration options (e.g.,

`CONFIG_EXT2_FS_XATTR` for [ext2/3/4][ext2]) and the underlying filesystem

you use for libprojfs should be mounted with appropriate settings

(e.g., [user_xattr][xattr-ext2] for ext2/3/4).



If you are using a [Docker](https://www.docker.com) container, you

may need to ensure the `fuse` kernel module is installed on your

host OS, and `user.*` extended attributes are supported on your host's

filesystem.  See the [Using Docker containers][build-docker] section for

more details.



To test libprojfs with the Microsoft VFSForGit `MirrorProvider`

(as we do not support the primary VFSForGit GVFS provider yet), .NET Core

must be installed and parts of the VFSForGit project built.  See the

[Building and Running MirrorProvider][build-mirror] section for details.



## Contributing



Thank you for your interest in libprojfs!



We welcome contributions; please see our [CONTRIBUTING](CONTRIBUTING.md)

guidelines and our contributor [CODE_OF_CONDUCT](CODE_OF_CONDUCT.md).



## Licensing



The libprojfs library is licensed under the [LGPL v2.1](COPYING).



See the [NOTICE](NOTICE) file for a list of other licenses used in the

project, and the comments in each file for the licenses applicable to them.



## Development Roadmap



We are developing the libprojfs library first, using FUSE to prototype and

test its performance, before migrating functionality into a Linux kernel

module (assuming that proves to be necessary to meet our performance

criteria).



For more details on the planned development phases, see our

[design document][design-process].



## Authors



The libprojfs library is currently maintained and developed by

several members of GitHub's Engineering organization, including:



* [@chrisd8088](https://github.com/chrisd8088)

* [@kivikakk](https://github.com/kivikakk)

* [@wrighty](https://github.com/wrighty)



You can also contact the GitHub project team at

[[email protected]](mailto:[email protected]).



[build]: docs/build-install.md

[build-docker]: docs/build-install.md#using-docker-containers

[build-mirror]: docs/build-install.md#building-and-running-mirrorprovider

[ci-master-redir]: https://dev.azure.com/asconnor/asconnor/_build/latest?definitionId=1&branchName=master

[ci-master-status]: https://dev.azure.com/asconnor/asconnor/_apis/build/status/github.libprojfs?branchName=master

[design-linux]: docs/design.md#vfsforgit-on-linux

[design-process]: docs/design.md#development-process

[ext2]: https://www.kernel.org/doc/Documentation/filesystems/ext2.txt

[fanotify]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/fanotify.h

[fsnotify]: https://github.com/torvalds/linux/blob/master/include/linux/fsnotify_backend.h

[fuse-man]: http://man7.org/linux/man-pages/man4/fuse.4.html

[fuse-mod]: https://www.kernel.org/doc/Documentation/filesystems/fuse.txt

[inotify]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/inotify.h

[libfuse]: https://github.com/libfuse/libfuse

[winprojfs]: https://docs.microsoft.com/en-us/windows/desktop/api/_projfs/

[vfs4git]: https://github.com/Microsoft/VFSForGit

[vfs4git-mirror]: https://github.com/Microsoft/VFSForGit/tree/features/linuxprototype/MirrorProvider

[xattr]: http://man7.org/linux/man-pages/man7/xattr.7.html

[xattr-ext2]: http://man7.org/linux/man-pages/man5/ext4.5.html#MOUNT_OPTIONS