Re: [LSF/MM/BPF TOPIC] statx attributes

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On Thu, Mar 7, 2024 at 7:36 AM Steve French <smfrench@xxxxxxxxx> wrote:
>
> Following up on a discussion a few years ago about missing STATX
> attributes, I noticed a case recently where some tools on other OS
> have an option to skip offline files (e.g. the Windows equivalent of
> grep, "findstr", and some Mac tools also seem to do this).
>

Which API is used in other OS to query the offline bit?
Do they use SMB specific API, as Windows does?

> This reminded me that there are a few additional STATX attribute flags
> that could be helpful beyond the 8 that are currently defined (e.g.
> STATX_ATTR_COMPRESSED, STATX_ATTR_ENCRYPTED, STATX_ATTR_NO_DUMP,
> STATX_ATTR_VERITY) and that it be worthwhile revisiting which
> additional STATX attribute flags would be most useful.

I agree that it would be interesting to talk about new STATX_ attributes,
but it should already be covered by this talk:
https://lore.kernel.org/linux-fsdevel/2uvhm6gweyl7iyyp2xpfryvcu2g3padagaeqcbiavjyiis6prl@yjm725bizncq/

We have a recent example of what I see as a good process of
introducing new STATX_ attributes:
https://lore.kernel.org/linux-fsdevel/20240302220203.623614-1-kent.overstreet@xxxxxxxxx/
1. Kent needed stx_subvol_id for bcachefs, so he proposed a patch
2. The minimum required bikeshedding on the name ;)
3. Buy in by at least one other filesystem (btrfs)

w.r.t attributes that only serve one filesystem, certainly a requirement from
general purpose userspace tools will go a long way to help when introducing
new attributes such as STATX_ATTR_OFFLINE, so if you get userspace
projects to request this functionality I think you should be good to go.

>
> "offline" could be helpful for fuse and cifs.ko and probably multiple
> fs to be able to report,

I am not sure why you think that "offline" will be useful to fuse?
Is there any other network fs that already has the concept of "offline"
attribute?

> but there are likely other examples that could help various filesystems.

Maybe interesting for network fs that are integrated with fscache/netfs?
It may be useful for netfs to be able to raise the STATX_ATTR_OFFLINE
attribute for a certain cached file in some scenarios?

As a developer of HSM API [1], where files on any fs could have an
"offline" status,
STATX_ATTR_OFFLINE is interesting to me, but only if local disk fs
will map it to
persistent inode flags.

When I get to it, I may pick a victim local fs and write a patch for it.

Thanks,
Amir.

[1] https://github.com/amir73il/fsnotify-utils/wiki/Hierarchical-Storage-Management-API





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