Editing ISO 9660 (section)

=== SUSP ===

''System Use Sharing Protocol'' (SUSP, [[IEEE]] P1281) provides a generic way of including additional properties for any directory entry reachable from the primary volume descriptor (PVD). In an ISO 9660 volume, every directory entry has an optional ''system use area'' whose contents are undefined and left to be interpreted by the system.  SUSP defines a method to subdivide that area into multiple system use fields, each identified by a two-character signature tag.  The idea behind SUSP was that it would enable any number of independent extensions to ISO 9660 to be created and included on a volume without conflicting. It also allows for the inclusion of property data that would otherwise be too large to fit within the limits of the system use area.

SUSP defines several common tags and system use fields:

* <code>CE</code>: Continuation area
* <code>PD</code>: Padding field
* <code>SP</code>: System use sharing protocol indicator
* <code>ST</code>: System use sharing protocol terminator
* <code>ER</code>: Extensions reference
* <code>ES</code>: Extension selector

Other known SUSP fields include:

* <code>AA</code>: Apple extension, preferred
* <code>BA</code>: Apple extension, old (length attribute is missing)
* <code>AS</code>: Amiga file properties
* <code>ZF</code>: zisofs compressed file, usually produced by program mkzftree or by libisofs. Transparently decompressed by Linux kernel if built with CONFIG_ZISOFS.<ref>{{cite web|title=linux/fs/isofs/Kconfig|website= [[GitHub]]|date= 23 January 2022|url= https://github.com/torvalds/linux/blob/master/fs/isofs/Kconfig}}</ref>
* <code>AL</code>: records [[Extended file attributes|Extended File Attributes]], including [[Access control list|ACLs]]. Proposed by [[libburnia]], supported by libisofs.<ref>{{cite web|title=Arbitrary Attribute Interchange Protocol|url=https://dev.lovelyhq.com/libburnia/web/wiki/AAIP}}</ref>

The Apple extensions do not technically follow the SUSP standard; however the basic structure of the AA and AB fields defined by Apple are [[Forward compatibility|forward compatible]] with SUSP; so that, with care, a volume can use both Apple extensions as well as RRIP extensions.