Re: [RFC PATCH v2 1/2] vfs: add provenance time (ptime)

[Pedro Falcato <pfalcato@suse.de>]

On Wed, Oct 28, 2026 at 02:47:27PM +0100, koraynilay wrote:
> Add provenance time (ptime), indicating the time when a file or
> directory was created. This is user-settable via file_setattr() and
> retrievable via statx(2) (using STATX_PTIME) or file_getattr().
> 
> The semantics of when to preserve this new timestamp are the same as
> mtime, the idea being that there is a correspondence like this:
> 
> ctime <-> btime
> mtime <-> ptime
> 
> so every operation (copying, moving, ...) that currently preserves mtime
> should also preserve ptime.
> 
> Furthermore, in order to avoid the legacy FS_IOC_FSSETXATTR accepting
> FS_XFLAG_PTIME, add an FS_FILE_ATTR_XFLAGS_MASK mask to support new
> xflags, and use it in fileattr_to_file_attr()/file_attr_to_fileattr() to
> allow ptime to be used with the file_setattr()/file_getattr() syscalls.

Random comment, but: could this be doable with xattrs instead? I'm not sure
where I would put the xattrs code (if in userspace exclusively, or if hooking
the VFS up with this, or if doing it on the filesystem side), but it would
surely be less disruptive than modifying a bunch of filesystems one-by-one.

This patch is quite simple, but changing btrfs, then ext4, xfs, etc is a
mess, and inevitably you can't get these timestamps until you upgrade your
filesystems.

-- 
Pedro