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

[koraynilay]

On Mon Nov 2, 2026 at 3:00 PM CET, Amir Goldstein wrote:
> 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/

Thanks, I did not think of adding a dynamic mask like that, I will look
into it and implement it for v4.

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

So after adding fsx_xflags_mask to file_kattr, every filesystem would
populate fsx_xflags_mask with all the returned (== supported) FS_XFLAG_*
in their own specific .fileattr_get, correct?

Best,
koraynilay

> Thanks,
> Amir.

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