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

[koraynilay]

On Wed Nov 4, 2026 at 12:33 PM CET, Jan Kara wrote:
> 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

Nice, thank you!

Best,
koraynilay

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