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CDMI Imports and Exports
CDMI containers (and data objects) can have metadata attached to indicate if they are a junction in a namespace, and to indicate if a given namespace entity is exported via other identifiers/access methods.
Definitions:
Definition from SNIA Dictionary - https://www.snia.org/education/online-dictionary/term/namespace
[General] A domain of identifiers.
[File System] The set of valid names recognized by a file system.
[Management] In CIM and WBEM, a collection of object definitions and instances that are logically consistent.
[NVMe] Formatted non-volatile storage that may be accessed by a host. For example, an NVMe namespace may contain logical blocks for storing data or key-value pairs for storing data.
Definition from NetApp - https://kb.netapp.com/onprem/ontap/da/NAS/What_are_junction_paths%3F
A junction is formed when a volume is mounted to a mount point below the root, and is used to create a file-system tree.
Also called "Union Mount" file systems.
Definition from Linux Kernel - https://docs.kernel.org/filesystems/overlayfs.html
An overlay filesystem combines two filesystems - an 'upper' filesystem and a 'lower' filesystem. When a name exists in both filesystems, the object in the 'upper' filesystem is visible while the object in the 'lower' filesystem is either hidden or, in the case of directories, merged with the 'upper' object.
Clause "13.2 Container object export details" teaches a standardized way to specify export metadata for containers to be exported via CDMI, NFS, CIFS and WebDAV. This same approach is extensible to other protocols such as S3 (See #283). There have been plans to create something similar for data objects (e.g. exporting LUNs stored as files or objects).
Clause "5.8 Object references" teaches a standardized way to specify that a CDMI container points to a different CDMI container. While this provides the ability for CDMI to represents soft links in a filesystem, it is insufficient to represent hard links and cross-protocol links that cannot be fully specified via a URI.
Add a new section to clause 13 describing imports.