[RFC PATCH 03/24] erofs: add Errno in Rust

[Ariel Miculas]

On 24/09/26 09:04, Gao Xiang wrote:
> 
> 
> On 2024/9/26 08:40, Gao Xiang wrote:
> > 
> > 
> > On 2024/9/26 05:45, Ariel Miculas wrote:
> 
> ...
> 
> > > 
> > > I honestly don't see how it would look good if they're not using the
> > > existing filesystem abstractions. And I'm not convinced that Rust in the
> > > kernel would be useful in any way without the many subsystem
> > > abstractions which were implemented by the Rust for Linux team for the
> > > past few years.
> > 
> > So let's see the next version.
> 
> Some more words, regardless of in-tree "fs/xfs/libxfs",
> you also claimed "Another goal is to share the same code between user
> space and kernel space in order to provide one secure implementation."
> for example in [1].
> 
> I wonder Rust kernel VFS abstraction is forcely used in your userspace
> implementation, or (somewhat) your argument is still broken here.

Of course the implementations cannot be identical, but there is a lot of
shared code between the user space and kernel space PuzzleFS
implementations. The user space implementation uses the fuser [1] crate
and implicitly its API for implementing the read/seek/list_xattrs etc.
operations, while the kernel implementation uses the Rust filesystem
abstractions.

While it's currently not possible to use external crates in the Linux
kernel (maybe it won't ever be), one area for improvement would be to
keep the shared code between these PuzzleFS implementations in the
kernel and publish releases to crates.io from there. In this way it will
be obvious which parts of the code are shared and they will actually be
shared (right now the code is duplicated).

I've actually touched on these points [2] during my last year's
presentation of PuzzleFS at Open Source Summit Europe [3].

And here [4] you can see the space savings achieved by PuzzleFS. In
short, if you take 10 versions of Ubuntu Jammy from dockerhub, they take
up 282 MB. Convert them to PuzzleFS and they only take up 130 MB (this
is before applying any compression, the space savings are only due to
the chunking algorithm). If we enable compression (PuzzleFS uses Zstd
seekable compression), which is a fairer comparison (considering that
the OCI image uses gzip compression), then we get down to 53 MB for
storing all 10 Ubuntu Jammy versions using PuzzleFS.

Here's a summary:
# Steps

* I’ve downloaded 10 versions of Jammy from hub.docker.com
* These images only have one layer which is in tar.gz format
* I’ve built 10 equivalent puzzlefs images
* Compute the tarball_total_size by summing the sizes of every Jammy
  tarball (uncompressed) => 766 MB (use this as baseline)
* Sum the sizes of every oci/puzzlefs image => total_size
* Compute the total size as if all the versions were stored in a single
  oci/puzzlefs repository => total_unified_size
* Saved space = tarball_total_size - total_unified_size

# Results
(See [5] if you prefer the video format)

| Type | Total size (MB) | Average layer size (MB) | Unified size (MB) | Saved (MB) / 766 MB |
| --- | --- | --- | --- | --- |
| Oci (uncompressed) | 766 | 77 | 766 | 0 (0%) |
| PuzzleFS uncompressed | 748 | 74 | 130 | 635 (83%) |
| Oci (compressed) | 282 | 28 | 282 | 484 (63%) |
| PuzzleFS (compressed) | 298 | 30 | 53 | 713 (93%) |

Here's the script I used to download the Ubuntu Jammy versions and
generate the PuzzleFS images [6] to get an idea about how I got to these
results.

Can we achieve these results with the current erofs features?  I'm
referring specifically to this comment: "EROFS already supports
variable-sized chunks + CDC" [7].

[1] https://docs.rs/fuser/latest/fuser/
[2] https://youtu.be/OhMtoLrjiBY?si=iuk7PstznEUgnr4g&t=1150
[3] https://osseu2023.sched.com/event/1OGjk/puzzlefs-the-next-generation-container-filesystem-armand-ariel-miculas-cisco-systems
[4] https://youtu.be/OhMtoLrjiBY?si=jwReE1qjs1wXLUCr&t=1732
[5] https://youtu.be/OhMtoLrjiBY?si=Nhlz8FJ9CGnwgOlS&t=1862
[6] https://gist.github.com/ariel-miculas/956056f213db2d3027905c61264d160b
[7] https://github.com/project-machine/puzzlefs/issues/114#issuecomment-2367039464

Regards,
Ariel

> 
> [1] https://lore.kernel.org/r/20230609-feldversuch-fixieren-fa141a2d9694@brauner
> 
> Thanks,
> Gao Xiang
> 
> > 
> > Thanks,
> > Gao Xiang
> > 
> > > 
> > > Cheers,
> > > Ariel
> > > 
>