3. A well-behaved PKZIP/OpenVMS program should never produce
more than one sub-block with the same TagX value. Also,
there will never be more than one "extra" block of type
0x000c in a particular directory record.
-UNIX Extra Field (0x000d):
The following is the layout of the Unix "extra" block.
Note: all fields are stored in Intel low-byte/high-byte
order.
Value Size Description
----- ---- -----------
(UNIX) 0x000d 2 bytes Tag for this "extra" block type
TSize 2 bytes Size for the following data block
Atime 4 bytes File last access time
Mtime 4 bytes File last modification time
Uid 2 bytes File user ID
Gid 2 bytes File group ID
(var) variable Variable length data field
The variable length data field will contain file type
specific data. Currently the only values allowed are
the original "linked to" file names for hard or symbolic
links, and the major and minor device node numbers for
character and block device nodes. Since device nodes
cannot be either symbolic or hard links, only one set of
variable length data is stored. Link files will have the
name of the original file stored. This name is NOT NULL
terminated. Its size can be determined by checking TSize -
12. Device entries will have eight bytes stored as two 4
byte entries (in little endian format). The first entry
will be the major device number, and the second the minor
device number.
-PATCH Descriptor Extra Field (0x000f):
The following is the layout of the Patch Descriptor "extra"
block.
Note: all fields stored in Intel low-byte/high-byte order.
Value Size Description
----- ---- -----------
(Patch) 0x000f 2 bytes Tag for this "extra" block type
TSize 2 bytes Size of the total "extra" block
Version 2 bytes Version of the descriptor
Flags 4 bytes Actions and reactions (see below)
OldSize 4 bytes Size of the file about to be patched
OldCRC 4 bytes 32-bit CRC of the file to be patched
NewSize 4 bytes Size of the resulting file
NewCRC 4 bytes 32-bit CRC of the resulting file
Actions and reactions
Bits Description
---- ----------------
0 Use for auto detection
1 Treat as a self-patch
2-3 RESERVED
4-5 Action (see below)
6-7 RESERVED
8-9 Reaction (see below) to absent file
10-11 Reaction (see below) to newer file
12-13 Reaction (see below) to unknown file
14-15 RESERVED
16-31 RESERVED
