---------- Forwarded Message ---------- Subject: Re: util-linux: libblkid: UDF superblock Date: Sunday 30 November 2014, 12:51:54 From: Pali Rohár <pali.rohar@xxxxxxxxx> To: Karel Zak <kzak@xxxxxxxxxx> On Sunday 30 November 2014 12:36:49 Pali Rohár wrote: > Hello! > > I looked at UDF specifications 1.50 [1] and 2.01 [2] and then > on libblkid UDF superblock code. > > If I understand libblkid udf code then it set LABEL string > from Primary Volume Descriptor --> VolumeIdentifier. This > field can be set by mkudffs --vid= option. > > But in both UDF specifications for LogicalVolumeIdentifier is > written: > > === > This field is extremely important in logical volume > identification when multiple media are present within a > jukebox. This name is typically what is displayed to the > user. === > > LogicalVolumeIdentifier can be set by mkudffs --lvid= option. > > About VolumeIdentifier (which is used by libblkid udf code) > there is only one part in both specifications: > > === > Part 3 ISO/IEC 13346 (in 2.01: ECMA 167) contains various > Identifiers which, depending upon the implementation, maybe > have to be presented to the user. > * VolumeIndentifier > === > > So I think that it is better to use LogicalVolumeIdentifier > for libblkid LABEL. And not current VolumeIdentifier. > > What do you think? > > See also discussion about these identifiers at [3]. > > > And I have another question. UDF does not support UUID > identifiers. But in both specifications there is something > which can be used. Read description about > VolumeSetIdentifier: > > === > Interpreted as specifying the identifier for the volume set. > > The first 16 characters of this field should be set to unique > value. The remainder of the field may be set to any allowed > value. Specifically, software generating volumes conforming to > this specification shall not set this volume to a fixed or > trivial value. Duplicate disks which are intended to be > identical may contain the same value in this field. > > NOTE: The intended purpose of this is to guarantee Volume Sets > with unique identifiers. The first 8 characters of the unique > part should come from CS0 hexadecimal representation of a > 32-bit time value. The remaining 8 characters are fee for > implementation use. > === > > So first 16 characters are good candidate for libblkid UUID. > What do you think about it? > > mkudffs set first 8 characters of VolumeSetIdentifier really > to that time time. Next characters can be configured by > mkudffs option --vsid=. Default is fixed "LinuxUDF". But we > still have unique time identifier. > > > [1] - http://www.osta.org/specs/pdf/udf150.pdf > [2] - http://www.osta.org/specs/pdf/udf201.pdf > [3] - > http://superuser.com/questions/366808/in-udf-whats-the-differ > ence-between-a-volume-identifier-volume-set-identifier Now I looked at newfs_udf implementation (part of UDFclient package [1], alternative to mkudffs) and it show this warning message newfs_udf: no logical volume name passed; not creating logical volume descriptor if you do not set -L option: -L volumename use `volumename' as logical volume name (discname) which is presented as discname -- good candidate for LABEL. That volumename is LogicalVolumeIdentifier what I suggested to use as LABEL in previous name. By default VolumeIdentifier (option -P) is set to some random garbage and blkid identify UDF disk as: /dev/loop0: LABEL="555e3160" TYPE="udf" (I set volumename to human readable disk name) So now I think that linux blkid should for LABEL use LogicalVolumeIdentifier instead VolumeIdentifier. newfs_udf set by default for VolumeSetIdentifier some random 8 chars (not 16!) but allows you to set also first 8 by option -S. mkudffs does not allow you to set first 8 chars. They are always time stamp. [1] - http://www.13thmonkey.org/udfclient/ -- Pali Rohár pali.rohar@xxxxxxxxx -----------------------------------------
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