Integrated File System Introduction

Extended attributes

An extended attribute (EA) is information associated with an object that provides additional details about the object. The EA consists of a name, which is used to refer to it, and a value. The value can be text, binary data, or another type of data.

The EAs for an object exist only as long as the object exists.

EAs come in many varieties and can be used to contain a variety of information. You may need to be aware of the following three EAs, in particular:

.SUBJECT
A brief description of the content or purpose of the object.

.TYPE
The type of data in the object. The type of data might be text, binary, source for a program, a compiled program, or other information.

.CODEPAGE
The code page to be used for the object. The code page used for the object is also used for the EA associated with the object.

A period (.) as the first character of the name means that the EA is a standard system EA (SEA), which is reserved for system use.

Various objects in the various file systems may or may not have EAs. The QSYS.LIB and Independent ASP QSYS.LIB file systems support three predefined EAs: .SUBJECT, .TYPE, and .CODEPAGE. In the document library services (QDLS) file system, folders and documents can have any kind of EA. Some folders and documents may have EAs, and some may not. In the "root" (/), open systems (QOpenSys), and user-defined file systems, all directories, stream files, and symbolic links can have EAs of any kind. Some, however, may not have any EAs at all.

The Work with Object Links (WRKLNK) command can be used to display the .SUBJECT extended attribute (EA) for an object. There is no other integrated file system support through which applications or users can access and change EAs. The only exceptions to this rule are the Display a UDFS (DSPUDFS) and the Display Mounted File System Information (DSPMFSINF) CL commands, which present extended attributes to users.

EAs associated with some objects in the QDLS can, however, be changed through interfaces provided by the hierarchical file system (HFS). See Document Library Services File System (QDLS) and Optical File System (QOPT) for more information about these file systems.

If a client PC is connected to an iSeries server through OS/2 or Windows, the programming interfaces of the respective operating system (such as DosQueryFileInfo and DosSetFileInfo) can be used to query and set the EAs of any file object. OS/2 users can also change the EAs of an object on the desktop by using the settings notebook; that is, by selecting Sets on the pop-up menu associated with the object.

If you define extended attributes, use the following naming guidelines:

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