[RFC PATCH v2 0/2] add provenance time (ptime)

[koraynilay]

This is an initial implementation of a new timestamp to indicate the
time when a file/directory was initially created.

This patch series takes inspiration from the one by Sean Smith
<defendthedisabled@xxxxxxxxx> [1], but using
file_setattr()/file_getattr() as suggested by Darrick J. Wong
<djwong@xxxxxxxxxx> in [2].

The semantics of this new timestamp should be at least these:
- it should be the same as btime on a newly created file
- it's user-settable, so it can be preserved for backups, filesystem
  conversions, archives and any similar operation
- it should be preserved every time mtime gets preserved

and the correspondence with the other timestamps is as follows:

ctime <-> btime
mtime <-> ptime

Examples:
1) a .zsh_history file created in 2019, then after a few years the user
   decides to switch to another filesystem, copying the .zsh_history to
   the new home, in that case btime would have the timestamp of the copy
   and ptime would have the 2019 timestamp (just like mtime would have
   been preserved)
2) a symlink created in 2020 from the home directory to a /path going
   through the same process as the .zsh_history, in this case it would
   also make sense to sync the ptime to the 2020 timestamp instead of
   keeping only the btime (so the inode creation time).

The proof-of-concept code (for testing) for stat(1) and cp(1) is
available at https://github.com/koraynilay/coreutils (master branch)
(Note: these coreutils code changes are a prototype and won't be
submitted upstream as-is, but they work as expected in simple stat and
cp -a/--preserve=ptime tests)

Lastly, the name "provenance" and "ptime" are not final, I personally
don't have a strong opinion on any name, but while testing with stat(1)
I noticed that "Provenance" is definitely too long for the normal
output, so another option which would fit well is "Origin time",
abbreviated as "ntime" (OrigiN time) and not as "otime", as that would
conflict with btrfs' internal naming and create confusion.

v2 changes:
- fix permission bypass leading to ptime update on immutable and
  append-only files (found by sashiko[3])
- normalize ptime timestamp as done in fs/attr.c:notify_change() (found
  by sashiko[3])
- fix wording in vfs patch to be like the cover-letter

Thanks.

[1]: https://lore.kernel.org/20260405195007.1306-2-DefendTheDisabled@xxxxxxxxx
[2]: https://lore.kernel.org/20260407014129.GC6192@frogsfrogsfrogs
[3]: https://sashiko.dev/#/patchset/20261027220532.736352-1-koray.fra%40gmail.com

koraynilay (2):
  vfs: add provenance time (ptime)
  btrfs: add provenance time (ptime)

 fs/btrfs/btrfs_inode.h          |  4 ++++
 fs/btrfs/delayed-inode.c        |  6 ++++++
 fs/btrfs/inode.c                | 17 ++++++++++++++++-
 fs/btrfs/ioctl.c                | 12 +++++++++++-
 fs/btrfs/print-tree.c           |  1 +
 fs/btrfs/tree-log.c             |  3 +++
 fs/file_attr.c                  | 29 +++++++++++++++++++++++++++--
 fs/stat.c                       |  2 ++
 include/linux/fileattr.h        | 27 ++++++++++++++++++++++++---
 include/linux/stat.h            |  1 +
 include/uapi/linux/btrfs_tree.h |  3 ++-
 include/uapi/linux/fs.h         |  8 +++++++-
 include/uapi/linux/stat.h       |  7 ++++++-
 13 files changed, 110 insertions(+), 10 deletions(-)


base-commit: 65ba8f34ec886ec72b2c07ddc8cf3d815c32869d
-- 
2.56.0