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

[Jan Kara]

On Tue 03-11-26 15:26:20, koraynilay wrote:
> On Tue Nov 3, 2026 at 2:25 PM CET, Jan Kara wrote:
> > On Tue 27-10-26 23:05:30, koraynilay wrote:
> >> 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
> >
> > One thing I miss in this series is an explanation what this new timestamp is
> > good for. Because frankly, I don't miss such timestamp as a Linux user :).
> >
> > 								Honza
> 
> Hello, my concrete use-cases are backups and filesystem conversions.
> 
> For backups, my setup is btrfs and using btrbk (so btrfs send to my nas
> with ssh) and the only missing thing from the backup is the timestamp of
> file creation (which I'm currently working around using xattrs).
> 
> The situation that prompted me to finally start working on this RFC
> PATCH was when I wanted to merge 2 btrfs FSs and the only way of doing
> that (AFAIK at least) is using cp/rsync, which can't set the creation
> time since btime is immutable. The workaround I used was the same as
> with backups, so with xattrs, but noticed that some files (symlinks)
> wouldn't accept xattrs, so I looked into it and found out xattrs are
> only for regular files/dirs.
> 
> (also see https://lore.kernel.org/DMGS4KQLY24Q.14MUTR6U93GIC@xxxxxxxxx/)

Ah, OK, I think I finally understand why do you want this. Thanks for
explanation!

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR