Re: [PATCH RFC 0/2] prototype: improve timestamp handling

["Darrick J. Wong" <djwong@kernel.org>]

Crumbs, apparently I forgot ever to send this message. :(

On Wed, Apr 16, 2025 at 04:43:31PM +0200, Luca Di Maio wrote:
> Hi all,
> 
> This is an initial prototype to improve XFS's prototype file
> functionality in scenarios where FS reproducibility is important.
> 
> Currently, when populating a filesystem with a prototype file, all generated inodes
> receive timestamps set to the creation time rather than preserving timestamps from
> their source files.
> 
> This patchset extends the protofile handling to preserve original timestamps (atime,
> mtime, ctime) across all inode types. The implementation is split into two parts:
> 
> - First patch extends xfs_protofile.in to track origin path references for directories,
> character devices and symlinks, similar to what's already implemented for regular files.
> 
> - Second patch leverages these references to read timestamp metadata from source files
> and populate it into the newly created inodes during filesystem creation.
> 
> At the moment, the new `xfs_protofile` generates a file that results
> invalid for older `mkfs.xfs` implementations. Also this new implementation
> is not compatible with older prototype files.
> 
> I can imagine that new protofiles not working with older `mkfs.xfs`
> might not be a problem, but what about backward compatibility?
> I didn't find references on prototype file compatibility, is a change
> like this unwanted?

I think it'd be more ergonomic for mkfs users to introduce an alternate
implementation that uses nftw() to copy whole directory trees (like
mke2fs -d does) instead of revising a 52-year old file format to support
copying attrs of non-regular files.  Then we can move people to a
mechanism that doesn't require cli options for supporting spaces in
filenames and whatnot.

--D

> If so, what do you think of a versioned support for prototype files?
> I was thinking something on the lines of:
> 
> - xfs_protofile
>   - if the new flag:
>     - set the first comment accordingly
>     - add the additional information
>   - else act as old one
> 
> - proto.c
>   - check if the doc starts with the comment `:origin-files enabled`
> 	(for example)
>   - if so, this is the new format
>   - else old format
> 
> Eager to know your thoughts and ideas
> Thanks
> L.
> 
> Luca Di Maio (2):
>   xfs_proto: add origin also for directories, chardevs and symlinks
>   proto: read origin also for directories, chardevs and symlinks. copy
>     timestamps from origin.
> 
>  mkfs/proto.c          | 49 +++++++++++++++++++++++++++++++++++++++++++
>  mkfs/xfs_protofile.in | 12 +++++------
>  2 files changed, 55 insertions(+), 6 deletions(-)
> 
> --
> 2.49.0
>