[PATCH] erofs: support metadata compression

[Gao Xiang]

Hi Bo,

On 2025/7/8 20:01, Bo Liu wrote:
> Filesystem metadata has a high degree of redundancy, so
> should compress well in the general case.
> To implement this feature, we make a special on-disk inode
> which keeps all metadata as its data, and then compress the
> special on-disk inode with the given algorithm.
> 
> Signed-off-by: Bo Liu <liubo03 at inspur.com>

I'm working on erofs-utils support for this feature, but
before that I tend to support optional metadata compression,
which means

if the bit 63 of nid is set, the inode itself metadata compressed.
if not, just uses the current way.

Because that we could enable image incremental builds so that
we don't have to rewrite the base inodes again.

Thanks,
Gao Xiang