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In order to simplify backup/restore of DNE striped directories, it would be useful to have new llapi_dir_create_from_xattr() and llapi_dir_default_from_xattr() interfaces that can use the raw trusted.lmv xattr read from the directory.
We may also consider allowing setxattr(dirfd, "trusted.lmv") on a (empty?) directory to trigger DNE restriping of the directory. If the directory is empty, this is a trivial operation, and would allow tools like tar and possibly rsync to properly backup and restore directories without the need for specialized tools.
As with file striping, the setxattr() and llapi_dir_*_from_xattr() interfaces should take the xattrs as a hint, using only the header information (lum_stripe_count, lum_hash_type) as applicable to the local filesystem configuration (e.g. limit lum_stripe_count to the local number of MDTs) and ignoring specific MDT assignments.
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