X.2 File system
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## X.2 File system

### X.2.1 UDF File System

The reader shall be able to read a logical format conforming to UDF 2.5 on BD-RE media and shall be able to read a logical format conforming to UDF 2.6 on BD-R media.

The creator shall be able to create a logical format conforming to UDF 2.5 on BD-RE media and shall be able to create a logical format conforming to UDF 2.6 on BD-R media.

The updater shall be able to update a logical format conforming to UDF 2.5 on BD-RE media and shall be able to update a logical format conforming to UDF 2.6 on BD-R media, without updating the UDF revision level of the file system already recorded on the media.

Options or extensions defined in UDF are required or restricted as specified in the following sub-sections, and in the media specific sub-sections.

### Note

1. Though the names of the files within the DICOM File-set are restricted by PS3.10, other files on the media may have longer file names up to 255 characters, which is the maximum for UDF 2.5 and UDF 2.6.

2. A Pseudo Overwrite Method is defined in the BD-R standard. It is used to make Write-Once media behave like rewritable media, hence sector format compatibility is ensured without multi-session or packet-written format. BD drives support Pseudo Overwrite management for BD-R. For Pseudo Overwrite Method the UDF version must be 2.6.

#### X.2.1.1 Interchange Levels

For the UDF Primary Volume Descriptor, both the Interchange Level and Maximum Interchange Level shall always be set to 2.

### Note

1. This means that the volume is not and will never be, part of a multi-volume set.

2. The Interchange Level and Maximum Interchange Level in the File Set Descriptor are defined by UDF to always be 3. This is despite the fact that restrictions specified for the DICOM File-set may be very similar to lower Interchange Levels specified in ECMA 167.

#### X.2.1.2 Virtual Partition Maps and Allocation Tables

Creators and updaters shall not write UDF Virtual Partition Maps and Virtual Allocation Tables on BD-RE and BD-R media, since pseudo overwrite management is performed in the drive.

#### X.2.1.3 Sparable Partition Maps and Sparing Tables

Creators and updaters shall not write UDF Sparable Partition Maps and Sparing Tables on BD-RE and BD-R media, since defect management is performed in the drive.

#### X.2.1.4 System Dependent Requirements

The reader shall not depend on any system dependent requirements as specified in UDF to be able to read the DICOM File-set, and shall not behave differently if they are present. Any unrecognized system dependent requirements shall be gracefully ignored.

Creators and updaters writing to a version of UDF that supports Named Streams shall use the default stream to write each file within the DICOM File-set.

### Note

1. For example, a particular form of file permissions, particular extended attributes or particular named streams may not be required or affect application behavior.

2. This does not mean that Extended Attributes or Named Streams may not be present and associated with files within the DICOM File-set.

#### X.2.1.5 Permissions and File Characteristics

Creators and updaters shall always create permissions for files within the DICOM File Set such that all users may create, read, write and delete all files, and all users may access, create, modify and delete all directories on all systems.

### Note

1. These requirements are equivalent to setting a Unix permission of 644 for files and 755 for directories.

2. The intent of these requirements is that for DICOM interchange media, implementation specific access control is not used or required.

The UDF File Identifier Descriptor for files within the DICOM File Set shall not specify a File Characteristic of "hidden."

#### X.2.1.6 File Types

The UDF File Types within the DICOM File Set shall only be files (that is a File Type of 0, meaning unspecified interpretation) or symbolic links to files (that is a File Type of 12).

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