Re: [RFC PATCH v3 1/5] vfs: add provenance time (ptime)

[Amir Goldstein]

On Sun, Nov 1, 2026 at 2:57 AM koraynilay <koray.fra@xxxxxxxxx> 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.
>
> [ This is a re-implementation of the initial patch[1] by Sean Smith
>   <defendthedisabled@xxxxxxxxx>, following the advice[2] from Darrick J.
>   Wong <djwong@xxxxxxxxxx> of using file_setattr() instead of updating
>   utimensat() ]
>
> [1]: https://lore.kernel.org/20260405195007.1306-2-DefendTheDisabled@xxxxxxxxx
> [2]: https://lore.kernel.org/20260407014129.GC6192@frogsfrogsfrogs
>
> Assisted-by: Gemini:3.8-flash-high antigravity-cli-1.4.7
> Signed-off-by: koraynilay <koray.fra@xxxxxxxxx>
> ---
>  fs/file_attr.c            | 33 +++++++++++++++++++++++++++++++--
>  fs/stat.c                 |  2 ++
>  include/linux/fileattr.h  |  5 +++++
>  include/linux/stat.h      |  1 +
>  include/uapi/linux/fs.h   |  8 +++++++-
>  include/uapi/linux/stat.h |  7 ++++++-
>  6 files changed, 52 insertions(+), 4 deletions(-)
>
> diff --git a/fs/file_attr.c b/fs/file_attr.c
> index 833e03810b24..c0645cb22bf3 100644
> --- a/fs/file_attr.c
> +++ b/fs/file_attr.c
> @@ -102,7 +102,7 @@ EXPORT_SYMBOL(vfs_fileattr_get);
>  static void fileattr_to_file_attr(const struct file_kattr *fa,
>                                   struct file_attr *fattr)
>  {
> -       __u32 mask = FS_XFLAGS_MASK;
> +       __u32 mask = FS_FILE_ATTR_XFLAGS_MASK;
>
>         memset(fattr, 0, sizeof(struct file_attr));
>         fattr->fa_xflags = fa->fsx_xflags & mask;
> @@ -110,6 +110,8 @@ static void fileattr_to_file_attr(const struct file_kattr *fa,
>         fattr->fa_nextents = fa->fsx_nextents;
>         fattr->fa_projid = fa->fsx_projid;
>         fattr->fa_cowextsize = fa->fsx_cowextsize;
> +       fattr->fa_ptime_sec = fa->fsx_ptime.tv_sec;
> +       fattr->fa_ptime_nsec = fa->fsx_ptime.tv_nsec;
>  }
>
>  /**
> @@ -141,15 +143,20 @@ EXPORT_SYMBOL(copy_fsxattr_to_user);
>  static int file_attr_to_fileattr(const struct file_attr *fattr,
>                                  struct file_kattr *fa)
>  {
> -       __u64 mask = FS_XFLAGS_MASK;
> +       __u64 mask = FS_FILE_ATTR_XFLAGS_MASK;

That is not the correct way to extend this API.
This fixed mask was added as a placeholder for
"We intend to add support for more xflags to selective filesystems":
https://lore.kernel.org/linux-fsdevel/20250329143312.1350603-2-amir73il@xxxxxxxxx/

Please see this POC patch for filesystems to publish their supported
xflags mask:
https://lore.kernel.org/linux-fsdevel/20250329143312.1350603-3-amir73il@xxxxxxxxx/

This will allow callers of file_getattr() to know if the filesystem
supports ptime
without trying to set it and failing.

Thanks,
Amir.