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1998-02-11
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+-------------------------------------------------------------------------
| $Id: Rock_Ridge_Amiga_Specific 2.4 1996/12/05 21:20:52 angela Exp $
+-------------------------------------------------------------------------
Description of the "AS" System Use Entry
The purpose of the "AS" System Use Entry is to record the complete set of
file attributes defined for the Amiga operating system. This includes the
protection flags plus an optional comment field. This System Use Entry is
optional. If no "AS" System Use Entry is recorded in the System Use Area
of a specific Directory Record, the defaults as described below shall be
used.
If more than one "AS" System Use Entry is recorded in the System Use
Field of a single Directory Record, or any extension thereof, only the
first such recorded "AS" Entry may contain Amiga Protection Bits. Any
additional "AS" Entry recorded for that same single Directory Record
shall have the PROTECTION bit of the Flags field set to ZERO.
If more than one "AS" System Use Entry is recorded, only the first of
them shall contain Amiga Protection Bits.
The format of the "AS" System Use Entry is as follows:
[1] "BP 1 to BP 2 - Signature Word" shall indicate that the System Use
Entry is a "AS" type System Use Entry. The bytes in this field shall
be (41)(53) ("AS").
[2] "BP 3 - Length (LEN_AS)" shall specify as an 8-bit number the length
in bytes of the "AS" System Use Entry. The number in this field shall
be 5, plus 4 if the PROTECTION bit of the Flags field is set to ONE,
plus LEN_COMMENT, if the COMMENT bit of the Flags field is set to ONE.
This field shall be recorded according to ISO 9660: 7.1.1.
[3] "BP 4 - System Use Entry Version" shall specify as an 8-bit number an
identification of the version of the "AS" System Use Entry. The
number in this field shall be 1 for this version. This field shall be
recorded according to ISO 9660:7.1.1.
[4] "BP 5 - Flags" shall contain bit field flags numbered 0 to 7 starting
with the least significant bit as follows:
TABLE 1. AS Flags
Position Name Value Interpretation
-------- ---------- ----- --------------
0 PROTECTION ONE All of the 32 Protection Bits are
recorded.
ZERO None of the 32 Protection Bits are
recorded.
1 COMMENT ONE A comment field is recorded.
ZERO No comment field is recorded.
2 COMMENT ONE If a comment is recorded, this comment
CONTINUE continues in next "AS" System Use Entry
of this System Use Area.
ZERO This is the last component of this
comment or no comment is recorded.
3-7 RESERVED ZERO Reserved for future use.
[5] "BP 6 to LEN_AS - Amiga Extensions" shall be defined as follows:
[6] If PROTECTION in the Flags field is set to ONE, then the first four
bytes of the Amiga Extension field shall contain Amiga protection
bits. All four bytes shall contain bit field flags numbered 0 to 7
starting with the least significant bit, with each bit representing
a valid Amiga file system attribute. The four bytes are recorded as
follows:
FIGURE 1. Amiga Protection Flags
BYTE 1 BYTE 2 BYTE 3 BYTE 4
User 0 Multiuser Flags Protection Bits
Please note that BYTE 1 starts at an odd address relative to the "AS"
System Use Entry.
Applications that are reading the Protection Flags must preserve all
four bytes. No bit shall be cleared or set.
[6a] "BYTE 1 - User Bitfields" are available to users and/or programmers
for their own purposes. Usually, they all should be set to ZERO.
[6b] "BYTE 2 - Reserved Bitfields" is reserved for future use and will be
enhanced consistent with future modifications, if any, to the Amiga
protection bits set. Shall be set all to ZERO.
[6c] "BYTE 3 - Multiuser Flags" shall contain the following Multiuser
Attribute Flags:
TABLE 2. Amiga Multiuser Attribute Flags
Position Character Value Interpretation
-------- --------- ----- --------------
0 d ONE Object shall be deletable for group
members.
ZERO Object shall not be deletable for group
members.
1 e ONE Object shall be executable for group
members.
ZERO Object shall not be executable for group
members.
2 w ONE Object shall be writable for group
members.
ZERO Object shall not be writable for group
members.
3 r ONE Object shall be readable for group
members.
ZERO Object shall not be readable for group
members.
4 d ONE Object shall be deletable for other
users.
ZERO Object shall not be deletable for other
users.
5 e ONE Object shall be executable for other
users.
ZERO Object shall not be executable for other
users.
6 w ONE Object shall be writable for other
users.
ZERO Object shall not be writable for other
users.
7 r ONE Object shall be readable for other
users.
ZERO Object shall not be readable for other
users.
[6d] "BYTE 4 - Protection Bits" shall contain the following Amiga
Attribute Flags:
TABLE 3. Protection Bits
Position Character Value Interpretation
-------- --------- ----- --------------
0 d ONE Object shall not be deletable for owner.
ZERO Object shall be deletable for owner.
1 e ONE Object shall not be executable for owner.
ZERO Object shall be executable for owner.
2 w ONE Object shall not be writable for owner.
ZERO Object shall be writable for owner.
3 r ONE Object shall not be readable for owner.
ZERO Object shall be readable for owner.
4 a ONE Object is considered to be archived.
ZERO Object is not considered to be archived.
Usually should be set to ZERO.
5 p ONE Object is a reentrant executable.
ZERO Object is not a reentrant executable.
6 s ONE Object is an executable script file,
currently either ARexx or AmigaDOS.
Future modifications to the Amiga
scripting capabilities may allow other
use of this flag.
ZERO Object it not an executable script file.
7 RESERVED ZERO Reserved for future use.
Please note that the use of bits 0 to 3 is inverted compared to the
use of the other bits to match the AmigaOS use of the 32 Amiga bits
exactly.
[7] If the COMMENT bit in the BP 5 is set to ONE, the following bytes
shall be interpreted as an Amiga Comment Extension.
FIGURE 2. Amiga Comment Extension
BYTE 1 BYTE 2 to LEN_COMMENT
LEN_COMMENT Comment
[7a] "BYTE 1 - LEN_COMMENT" shall contain the byte length of this part of
the comment stored in this System Use Entry including the length
byte itself. This field shall be recorded according to
ISO 9660:7.1.1.
[7b] "BYTE 2 to LEN_COMMENT - Comment" shall contain a comment string
providing descriptive information about the file system object
associated with this entry. There is no restriction on the content
of the comment, except that it shall not contain any (00) character,
though it is recommended that the comment is a displayable string.
The comment shall not be (00) terminated. The length of the recorded
comment shall be LEN_COMMENT-1.
If the COMMENT CONTINUE Flag in BP 5 is set, the comment shall
continue in the next "AS" System Use Field of this Direcory Record.
All comment parts (excluding the length byte) shall be concatenated
together, in the order in which they were recorded, until a COMMENT
CONTINUE flag with value ZERO is encountered, to obtain the entire
comment.
[8] The following default values shall be assumed for all unrecorded
components of the "AS" field.
It is acceptable not to record protection bits in the "AS" entry if
the default mapping of the "PX" entry according to TABLE 6 will
result in the correct Amiga protection bit settings for the object.
An empty "AS" entry need not be recorded. Filesystems shall make use
of the required "PX" entry if no "AS" entry or no protection bits in
that entry are present for an object.
TABLE 5. Default values for "AS"
Description Value
----------- -----
PROTECTION Defaults as described in table 6.
COMMENT COMMENT_LEN set to (01).
TABLE 6. Default Amiga Protection Bits
Byte Number Bit Position According "PX" bit or absolute value
----------- ------------ ------------------------------------
1 0 to 7 ZERO
2 0 to 7 ZERO
3 0 S_IWGRP
3 1 S_IXGRP
3 2 S_IWGRP
3 3 S_IRGRP
3 4 S_IWOTH
3 5 S_IXOTH
3 6 S_IWOTH
3 7 S_IROTH
4 0 inverted S_IWUSR
4 1 inverted S_IXUSR
4 2 inverted S_IWUSR
4 3 inverted S_IRUSR
4 4 ZERO
4 5 ZERO
4 6 ZERO
4 7 ZERO
When generating the multiuser flags, please note that a user who
wants to make a backup on CD-ROM usually does not want his data being
world-accessable, while someone, who creates a commercial CD-ROM
usually wants a world-wide-accessable CD-ROM.
FIGURE 3. "AS" System Use Entry
"A" "S" LEN_AS 1 FLAGS AMIGA EXTENSIONS
(BP1) (BP2) (BP3) (BP4) (BP5) (BP7 to LEN_AS)
This document has been developed by Angela Schmidt
<Angela.Schmidt@stud.uni-karlsruhe.de>, with the help of Andrew Young
<ayoung@mail.deltanet.com> (primary author of the Rock Ridge Interchange
Protocol and System Use Sharing Protocol), and is supported by Martin
Berndt <m_berndt@wanderer.gun.de> (author of AmiCDFS), Oliver Kastl
(author of CacheCDFS), Paul Reeves (author of AsimCDFS and MasterISO),
Heinz Wrobel <heinz@hwg.muc.de> and Bernhard Möllemann
<zza@mhystic.hall.sub.org>.
For suggestions, please email Angela Schmidt
<Angela.Schmidt@stud.uni-karlsruhe.de>.