mkfs.erofs fails (failed to build shared xattrs, err 61)

[Gael Donval]

On Tue, 2024-03-12 at 19:37 +0800, Gao Xiang wrote:
> 
> 
> On 2024/3/12 19:07, Gael Donval wrote:
> > > On 2024/3/12 18:44, Gao Xiang wrote:
> > > > Hi Gael,
> > > > 
> > > > On 2024/3/12 17:57, Gael Donval wrote:
> > > > > Dear list,
> > > > > 
> > > > >      $ mkdir foo && touch foo/bar && mkfs.erofs foo.erofs.img
> > > > > foo
> > > > >      mkfs.erofs 1.7.1
> > > > >      <E> erofs: failed to build shared xattrs: [Error 61] No
> > > > > data
> > > > > available
> > > > >      <E> erofs:     Could not format the device : [Error 61]
> > > > > No
> > > > > data available
> > > > > That is at a location backed by BTRFS (btrfs-progs v6.7.1) on
> > > > > kernel 6.8.0.
> > > > > 
> > > > > If I use a TMPFS-supported folder instead all goes well.
> > > > > 
> > > > > 
> > > > > Of course (NB "-x-1"),
> > > > > 
> > > > >      $ mkdir foo && touch foo/bar && mkfs.erofs -x-1
> > > > > foo.erofs.img
> > > > > foo
> > > > > 
> > > > > also works but is not how mkfs.erofs is meant to work in the
> > > > > general case.
> > > > 
> > > > Thanks for your feedback.
> > > > 
> > > > Currently I don't have some BTRFS environment, I could set up
> > > > one
> > > > later.
> > > > Yet in parallel could you provide a full message of
> > > > "strace mkfs.erofs -x-1 foo.erofs.img foo" on BTRFS too?
> > > 
> > > sorry, I meant "strace mkfs.erofs foo.erofs.img foo"
> > 
> > Hi,
> > 
> > Here it is.
> > 
> 
> The problem here is that BTRFS could extract their internal
> xattrs ("inode properties") in their own namespace which
> don't belong to the original file itself like:
> 
> XATTR_BTRFS_PREFIX "compression" -> btrfs.compression = zstd
> 
> I think I need to introduce something to formally ignore
> these xattrs like: `--xattrs-exclude=pattern`:
> https://urldefense.com/v3/__https://www.gnu.org/software/tar/manual/html_node/Extended-File-Attributes.html__;!!PDiH4ENfjr2_Jw!Dqu_tH2zT_TKEhHNi2CZToYlmYFeZayWE1BQVQjZBZq4egjYS1bAVS7BasQJ9BETJoVINPEB-p06y7izIUmWk-2VnofOQZwLrw$
>  [gnu[.]org]

I think that could work but a mode where EROFS keep the XATTRS it
recognises and ignore the ones it doesn't would probably prove useful
in the general case. 

I would suggest a --strict-xattrs mode behaving like it does today,
requiring explicit --xattrs-exclude to whitelist XATTRS.

The default would be a relaxed mode where ignored XATTRS are reported
on stderr at INFO level. Would that make sense and be alright?

Is there anything the BTRFS people could do to make their FS easier to
work with?

Gaël

> 
> Thanks,
> Gao Xiang
> 
> > Thanks for your help,
> > Gaël
> > 
> >