458 lines
20 KiB
Plaintext
458 lines
20 KiB
Plaintext
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Arbitrary Attribute Interchange Protocol
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Version 2.0
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Mar 18 2009
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Interchange of Persistent File Attributes
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by Thomas Schmitt - mailto:scdbackup@gmx.net
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Libburnia project - mailto:libburn-hackers@pykix.org
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AAIP is intended as companion of the Rock Ridge Interchange Protocol RRIP
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which under the general design of System Use Sharing Protocol SUSP extends
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ISO 9660 aka ECMA-119 filesystem semantics to match POSIX needs.
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Goal is to have for each file an arbitrary number of attributes which consist
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of two components (Name and Value) of arbitrary length and to have a compact
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representation of ACLs.
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This document describes a SUSP entry with Signature Word "AL" which collides
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neither with SUSP 1.12 nor with RRIP 1.12. The AL entry has been designed
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to be as similar to the RRIP entry SL as possible.
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The presence of AAIP shall be announced by a particular ER entry.
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Since the size of a SUSP entry is limited to 255, multiple entries may be
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needed to describe one component. The CE mechanism of SUSP shall be used to
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address enough storage if needed.
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AL entries and the ER entry of AAIP shall only be present if the ER entry
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of RRIP is present.
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-------------------------------------------------------------------------------
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System Entries Provided by this Specification
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* AL
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Description of the "AL" System Use Entry
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The entry has exactly the same layout as RRIP entry SL. One has to expect
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more data bytes than with SL, though, and any of the 256 possible byte values.
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The reader shall be prepared to detect and handle oversized data.
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One or more AL entries form the Attribute List of a file object with
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an even number of components. Each two consequtive components form a pair of
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Name and Value.
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The empty name indicates that the value is a compact representation of ACLs.
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Names must not contain byte value 0x00. Names which begin by bytes 0x01 to 0x1f
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represent names in particular namespaces. See below: Namespaces.
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The meaning of any other names or name parts is not specified by this document.
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All AL entries except the last one shall have the CONTINUE flag set. An AL
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entry with CONTINUE set to 0 indicates the end of the Attribute List.
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The format of the AL System Use Field is as follows:
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[1] "BP 1 to BP 2 - Signature Word" shall be (41)(4C) ("AL").
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[2] "BP 3 - Length" shall specify as an 8-bit number the length in bytes of
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the AL entry recorded according to ISO 9660:7.1.1.
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[3] "BP 4 - System Use Entry Version" shall be 1 as in ISO 9660:7.1.1.
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[4] "BP 5 - Flags" shall contain bit field flags numbered 0 to 7 starting
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with the least significant bit as follows:
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0 CONTINUE This AL entry continues in the next AL entry.
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All other bits shall be set to 0.
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[5] "BP 6 to Length - Component Area" shall contain Component Records
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as described below.
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| 'A' | 'L' | LENGTH | 1 | FLAGS | COMPONENT AREA |
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Within AL entries each component (Name or Value) shall be recorded as one
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or more component records. If a component does not fit into the remaining
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space of an AL entry then it shall be continued in following AL entries.
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All Component Records of a component except the last one shall have the
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CONTINUE flag set. A Component Record with CONTINUE set to 0 indicates the end
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of the component. An eventually following Component Record starts the next
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component.
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-------------------------------------------------------------------------------
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The Component Record format is identical to the one of the SL entry.
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The complete form of the following summary can be found in RRIP 1.12 "4.1.3.1".
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In case of discrepancies, RRIP 1.12 is the decisive specification. Please
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inform the author of this document if you find such a discrepancy.
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Component Records shall be recorded contiguously within each Component Area,
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starting in the first byte of the Component Area. The last Component Record
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in the Component Area of an AL System Use Entry may be continued in the
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Component Area of the next recorded AL System Use Entry in the same
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System Use Area.
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Each Component Record shall have the following format:
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[A] "BP 1 - Component Flags" shall contain bit field flags numbered 0 to 7,
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starting with the least significant bit, as follows:
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0 CONTINUE This Component Record continues in the next
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AL Component Record.
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all others are RESERVED and shall be 0.
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[B] "BP 2 - Component Length (LEN_CP)" shall specify as an 8-bit number the
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number of component bytes in the Component Record. This length shall not
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include the first two bytes of the Component Record.
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If any of the bit positions 1-3 is set, the value of this field shall be
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set to ZERO and no Component Content shall be recorded.
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This field shall be recorded according to ISO 9660 Format section 7.1.1.
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[C] "BP 3 to 2 + LEN_CP - Component Content" shall contain the component
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bytes in the Component Record.
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| COMPONENT FLAGS | LEN_CP | COMPONENT BYTES |
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Example: Two pairs of "name"="long...content" and "one"="more" encoded as
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two AL entries
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Field 1 contains the Component Record of Name and one Component Record of
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Value :
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{ 'A', 'L', 255, 1, 1,
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0, 4, 'n', 'a', 'm', 'e',
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1, 255, 'l', 'o', 'n', 'g', ... 238 more bytes, 13 go to next AL ... }
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Field 2 contains the rest of "long...content" and the complete second pair.
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It marks the end of the Attribute List :
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{ 'A', 'L', 38, 1, 0,
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... 13 remaining bytes of the Component Record in first entry ...
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0, 7, 'c', 'o', 'n', 't', 'e', 'n', 't',
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0, 3, 'o', 'n', 'e',
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0, 4, 'm', 'o', 'r', 'e' }
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-------------------------------------------------------------------------------
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Namespaces
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AAIP provides a short notation for namespaces which uses a single non-printable
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byte at the start of the name.
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Reserved start bytes of names are
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0x01 to 0x1F
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The names of extended file attributes are traditionally organized in
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namespaces, which get expressed as first part of an attribute name up to a
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period "." character. It is also tradition that names are printable text,
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single words and especially contain no 0-bytes.
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AAIP does not enforce the use of any namespace but it urges that names in the
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following registered namespaces are used according to traditions.
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The namespaces "system." and "user." are available with many file system
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types. "system." is file system dependent and often restricted in the
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choice of names. "user." is portable and allows to choose about any name.
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Namespace "isofs." is defined for internal use of AAIP enhanced ISO 9660
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file systems. Names in this namespace should be registered at
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libburnia-project.org.
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Further namespaces may be registered at libburnia-project.org.
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The reserved start bytes of names have the following meaning
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0x01 escape reserved character at start of name
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0x02 namespace "system."
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0x03 namespace "user."
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0x04 namespace "isofs."
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0x05 namespace "trusted."
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0x06 namespace "security."
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0x07 to 0x1F shall not be used yet.
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Examples:
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Name "user.abc" with and without short notation. Both is allowed.
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0, 4, 0x03, 'a', 'b', 'c'
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0 8, 'u', 's', 'e', 'r', '.', 'a', 'b', 'c'
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Name "\003abc" (if really desired)
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0, 5, 0x01, 0x03, 'a', 'b', 'c'
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-------------------------------------------------------------------------------
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Specification of binary ACL representation as special Arbitrary Attribute
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The Name component of a binary ACL shall be of length 0.
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The Value shall be an arbitrary number of ACL Entries:
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[a] "BP 1 - Entry Flags" shall contain bit field flags numbered 0 to 7,
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starting with the least significant bit, as follows:
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0 EXEC indicates that this entry grants execute permission
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1 WRITE write permission
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2 READ read permission
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3 QUALIFIER indicates that one or more Qualifier Records follow
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4 - 7 TYPE
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shall contain the tag type of the ACL entry as four bit code:
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0 TRANSLATE Entry for a global map of name to numeric id
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Qualifier is a record of number and text
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1 ACL_USER_OBJ Permissions of owning user (as of PX entry)
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3 ACL_GROUP_OBJ Permissions of owning group (as of PX entry)
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5 ACL_MASK Restricts 10, 3, and 12 via logical AND
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6 ACL_OTHER Permissions of non-listed, non-owning users
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8 SWITCH_MARK Switch from "access" ACL to "default" ACL
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10 ACL_USER_N Permissions of arbitrary user. Qualifier is
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the numeric user id (max. 4 bytes).
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12 ACL_GROUP_N Permissions of arbitrary group. Qualifier is
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the numeric group id (max. 4 bytes).
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15 FUTURE_VERSION Will indicate that this document
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does not apply to the entry.
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The other values are reserved. Readers shall ignore them if
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they are not aware of updates of this document which would
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assign a meaning to them.
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The entries must match the permission bits of the PX entry. This shall obey the
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rule that ACL_USER_OBJ must match S_IRWXU, ACL_OTHER must match S_IRWXO,
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ACL_MASK - if present - must match S_IRWXG, else ACL_GROUP_OBJ must match
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S_IRWXG. If there is ACL_USER_N or ACL_GROUP_N there must also be ACL_MASK.
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A numeric qualifier is a binary number of variable length up to 4 bytes. The
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Most Significant Byte comes first. The number shall be the "POSIX File User ID"
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resp. "POSIX File Group ID" as also used in RRIP PX entries. The ids of owning
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user and owning group shall be taken from the PX entry of the file object.
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Optional TRANSLATE entries may associate user or group names with numeric
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ids to allow the reading system to remap the numeric ids. See below.
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The writer is not obliged to write them and the reader is not obliged to
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interpret them.
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The ACL entries belong to the "access" ACL of a file object. An optional
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SWITCH_MARK entry may direct further entries to the "default" ACL which
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is defined for directory objects. The EXEC bit of SWITCH_MARK shall be 1.
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The bits for WRITE, READ, QUALIFIER shall be 0.
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An eventually needed qualifier is stored in one or more Qualifier Records.
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[b] "BP 2 - Qualifier Record Head" shall be present only if QUALIFIER is set
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to 1. It shall give the number of Qualifier Bytes and eventually
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indicate that the qualifier continues in a Qualifier Record which comes
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imediately after this record.
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0 to 127 Q_LENGTH, the qualifier is complete by this record
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128 to 255 Q_LENGTH+128, the qualifier is continued by next record
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So a Qualifier Record can contain at most 127 Qualifier Bytes.
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This field shall be recorded according to ISO 9660 Format section 7.1.1.
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[c] "BP 3 to BP 2 + Q_LENGTH - Qualifier Bytes" shall be present only if
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QUALIFIER is set to 1 and hold the announced number of bytes of the
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user or group name.
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| ENTRY FLAGS [ | QUALIFIER HEAD | QUALIFIER BYTES | ]
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Example: From man 5 acl: u::rw-,u:lisa:rw-,g::r--,g:toolies:rw-,m::r--,o::r--
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"lisa" has user number 123, "toolies" has group number 65534
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{ 'A', 'L', 20, 1, 0,
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0, 0,
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0, 11, 0x16,
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0xAE, 1, 123,
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0x34,
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0xCE, 2, 255, 254,
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0x54,
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0x64 }
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Example: "Access" ACL and "default" ACL (0x81 is the switch mark)
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u::rwx,g::r-x,o::r-x, du::rwx,dg::r-x,dm::rwx,do::r-x,du:lisa:rwx
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{ 'A', 'L', 20, 1, 0,
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0, 0,
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0, 11, 0x17, 0x35, 0x65,
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0x81,
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0x17, 0x35, 0x57, 0x65,
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0xA7, 1, 123 }
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-------------------------------------------------------------------------------
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Association of Names and Numeric Identifiers
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The entry flag value 0x08 TRANSLATE is not a ACL entry of the hosting object
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but rather a global hint about the relation of roles, names and numeric ids.
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If it is recorded at all, then it shall be recorded with the first Directory
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Entry of the volume's root directory. According to the description of SUSP
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entry ER, this has to be "dot" or (00). Other than with ER, a TRANSLATE entry
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may not appear in the root of directory sub trees.
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An interested reader shall examine the Arbitrary Attributes of this Directory
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Entry in order to collect a translation table.
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The advised translation is: PX or AL Id number -> name -> local id number.
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The Qualifier Bytes of a TRANSLATE entry shall have the following format:
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[i] "BP 0 - Role" shall tell whether it is about a user name (role 0) or
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a group name (role 1). Other values are not allowed.
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[ii] "BP 1 to BP 8 - Numeric Id" shall hold the 32 bit POSIX Id number of the
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entry. This field shall be recorded according to ISO 9660:7.3.3.
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[iii] "BP 9 to End Of Qualifier - Name" shall hold the name bytes of this
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entry.
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| ROLE | NUMERIC ID | NAME |
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Example: User id number 123 gets associated with user name "lisa"
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0x08, 13, 0, 123,0,0,0, 0,0,0,123, 'l', 'i', 's', 'a',
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Example: A very long qualifier naming "His_Excellency_..._the_Boss" as user #1.
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This needs two qualifier records.
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0x08, 255, 0, 1,0,0,0, 0,0,0,1,
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'H', 'i', 's', '_', 'E', 'x', 'c', 'e', 'l', 'e',
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... 108 more bytes ...
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8, 't', 'h', 'e', '_', 'B', 'o', 's', 's',
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-------------------------------------------------------------------------------
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Specification of the ER System Use Entry Values for AAIP:
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This ER system entry shall only be present if the ER entry of RRIP is present.
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To be compliant with SUSP-1.12, this ER entry must be present if AL entries
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are present, and ES entries have to mark RRIP and AAIP entries.
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If for some reason compliance with SUSP-1.10 is intended, then this ER entry
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and the ES entries must not be present, although SUSP-1.10 would allow ER.
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(See below: Compatibility considerations.)
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The Extension Version number for this version of AAIP shall be 1.
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The Extension Identifier field shall be "AAIP_0200" with Identifier Length 9.
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The mandatory content form of the Extension Descriptor is
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"AL PROVIDES VIA AAIP 2.0 SUPPORT FOR ARBITRARY FILE ATTRIBUTES IN ISO 9660 IMAGES"
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The Description Length is 81.
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The recommended content of the Extension Source is
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"PLEASE CONTACT THE LIBBURNIA PROJECT VIA LIBBURNIA-PROJECT.ORG".
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The corresponding Source Length is 62.
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-------------------------------------------------------------------------------
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Compatibility Considerations
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This extension is supposed not to disturb any reader system which complies
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to SUSP-1.10:
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"6.2 Requirements for a Receiving System
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[...]
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Any System Use Field which the receiving system does not recognize
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is to be ignored and skipped."
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SUSP-1.12 extends this prescription by:
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"Any System Use Entry, with the exception of the set of System Use Entries
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defined in this document, following an "ES" System Use Entry that indicates
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an extension specification which the receiving system does not recognize
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shall be ignored and skipped."
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According to SUSP-1.12 the ER entry is mandatory for a conformant extension.
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It also prescribes that in the case that ER entries of RRIP and AAIP are
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present, then ES entries shall be used to separate RRIP entries from AAIP
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entries.
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SUSP-1.12 frowns on extensions which are not announced by ER. Nevertheless
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is does not totally outrule them.
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SUSP-1.10 does not specify ES entries at all and allows to have extension
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entries without announcing them by an ER entry. So if a second ER entry is
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not bearable, then the SUSP-1.10 downgrade of AAIP allows to omit the
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AAIP ER and the ES entries. But if there is the AAIP ER then there must be ES
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at the appropriate places. Else the format would explicitely violate SUSP-1.12.
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-------------------------------------------------------------------------------
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Model Relations:
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Attribute List ------------- [1:0..1] ------------- ACL
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[1:0..n] [1:0..n]
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Arbitrary Attribute ( [1:0..1] ACL ) Entry
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[1:2..2n] [1:0..1]
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Component ( [1..m:1..n] AL Field ) Qualifier
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[1:1..n] << one of >>
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Component Record / \
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[1..m:1..n] Translation Entry , Numeric Id
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AL Field | |
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[1:1..n] [1:1]
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\ /
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Qualifier Record
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-------------------------------------------------------------------------------
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Revoked drafts:
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The following outdated versions may be interpreted at read time but they
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shall not be written any more.
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AAIP-1.0
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Previous versions up to AAIP 1.0 used field signature "AA" rather than "AL".
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This nearly collides with "Apple ISO 9660 Extensions". The Apple "AA" field of
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version 1 has a length of 7, whereas the shortest first AAIP field "AA" had
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length 9.
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Beginning with AAIP 2.0, the field name has been changed to "AL".
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If a reader interprets old AAIP "AA" fields, then it must take precautions to
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distinguish them from Apple "AA" fields. But it is well compliant with AAIP 2.0
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to just ignore any kind of "AA" fields.
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AAIP 1.0 had ER signature "AAIP_0100".
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AAIP-0.2
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AAIP 0.2 with ER signature "AAIP_0002" allowed to announce and use a different
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signature than "AA". This was revoked because ES entries serve the purpose
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to distinguish AAIP entries from eventual "AA" entries of any other extension.
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Regrettably no reader (kernel) was found which neatly interprets ES. Many do
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not even recognize the RRIP-1.12 ER signatures "IEEE_P1282", "IEEE_1282".
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AAIP 0.2 defined two ACL types which did not make it into AAIP 1.0
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2 ACL_USER of arbitrary user, with name as qualifier
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4 ACL_GROUP of arbitrary group, with name as qualifier
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Their job was transferred to ACL_USER_N and ACL_GROUP_N which have numeric
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qualifiers.
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AAIP-0.0
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There was a draft AAIP 0.0 with ER signature "AAIP_2008A". It did not resemble
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the existing entry SL and was never implemented.
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-------------------------------------------------------------------------------
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References:
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ECMA-119 aka ISO 9660
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http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-119.pdf
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SUSP 1.12 (entries CE , PD , SP , ST , ER , ES)
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ftp://ftp.ymi.com/pub/rockridge/susp112.ps
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RRIP 1.12 (entries PX , PN , SL , NM , CL , PL , RE , TF , SF , obsolete: RR)
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ftp://ftp.ymi.com/pub/rockridge/rrip112.ps
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Apple ISO 9660 Extensions (entries AA and BA)
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http://developer.apple.com/technotes/fl/fl_36.html
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Amiga AS entry
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http://www.estamos.de/makecd/Rock_Ridge_Amiga_Specific
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zisofs entry ZF (prepared by zisofs-tools, written by mkisofs)
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http://freshmeat.net/projects/zisofs-tools/
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Program mkisofs emits entry XA
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ftp://ftp.berlios.de/pub/cdrecord/alpha
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-------------------------------------------------------------------------------
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This text is under
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Copyright (c) 2009 - 2010 Thomas Schmitt <scdbackup@gmx.net>
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It shall only be modified in sync with libisofs and other software which
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makes use of AAIP. Please mail change requests to mailing list
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<libburn-hackers@pykix.org> or to the copyright holder in private.
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Only if you cannot reach the copyright holder for at least one month it is
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permissible to modify this text under the same license as the affected
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copy of libisofs.
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If you do so, you commit yourself to taking reasonable effort to stay in
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sync with the other interested users of this text.
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