Re: [PATCH 1/2] fs/erofs: Add support for EROFS

[Gao Xiang]

Hi Glenn,

On 2023/7/17 11:51, Glenn Washburn wrote:
> On Mon, 17 Jul 2023 00:03:08 +0800
> Yifan Zhao <zhaoyifan@sjtu.edu.cn> wrote:
>
> > EROFS is a lightweight read-only filesystem designed for performance which
> > has already been widely used in several scenarios, such as Android system
> > partitions, container images, and rootfs for embedded devices.
> >
> > This patch brings EROFS uncompressed support. Now, it's possible to boot
> > directly through GRUB with an EROFS rootfs.
> >
> > EROFS compressed support will be developed later since it has more work
> > to polish.
>
> I would expect that a very small minority are using EROFS without compression.
> Does that also seem true to you? This is relevant because I believe GRUB is
> in a feature freeze, but if there were a compelling reason to include this in
> the upcoming release, Daniel might make an exception (just guessing). On the
> one hand, in favor of including the current code without compression in the
> next release is that its simple enough and doesn't touch existing code, so a
> bug should have minor impact on the rest of GRUB. On the other hand, if there
> is a low probability of its use, perhaps its not worth it. As it stands, it

Thanks for the reply!

EROFS can have per-file compression, which means some files could be compressed,
the others are not.  Therefore, the majority of rootfs can still be compressed,
but leave the real kernel image uncompressed though, so we could still boot
systems from EROFS filesystems with EROFS rootfs images.

One barrier to support EROFS compression is that there is no public LZ4 library
in grub (Yifan said there is one in the ZFS filesystem, but no generic one.)

Personally I'd suggest support uncompressed EROFS for now since it removes
another filesystem dependency of EROFS rootfs so we don't need to add another
partition for this.


> seems that GRUB is being released every couple years.

Ok, I think if we missed this release, we will wait for another two years.

Thanks,
Gao Xiang


> When you create an updated patch series, it would be much appreciated if you
> use --range-diff or --interdiff so that reviewers (me) can verify more easily
> the changes.
>
> > Signed-off-by: Yifan Zhao <zhaoyifan@sjtu.edu.cn>