求解：iso文件路径表分析

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A path table contains one record for each directory on the CD-ROM
(including the root directory). The format of a record is as follows:     length
     in bytes  contents
     --------  ---------------------------------------------------------
        1      N, the name length (or 1 for the root directory)
        1      0 [number of sectors in extended attribute record]
        4      number of the first sector in the directory, as a
                 double word
        2      number of record for parent directory (or 1 for the root
                 directory), as a word; the first record is number 1,
                 the second record is number 2, etc.
        N      name (or 0 for the root directory)
      0 or 1   padding byte: if N is odd, this field contains a zero; if
                 N is even, this field is omittedAccording to ISO9660, a directory name consists of at least one and not
more than 31 capital letters, digits and underscores. For DOS the upper
limit is eight characters. A path table occupies as many consecutive sectors as may be required to
hold all its records. The first record always begins in the first byte
of the first sector. Except for the single byte described above, no
padding is used between records; hence the last record in a sector is
usually continued in the next following sector. The unused part of the
last sector is filled with zeros.The records in a path table are arranged in a precisely specified order.
For this purpose, each directory has an associated number called its
level. The level of the root directory is 1. The level of each other
directory is one greater than the level of its parent. As noted above,
ISO9660 does not permit levels greater than 8.The relative positions of any two records are determined as follows:     (1) If the levels are different, the directory with the lower level
         appears first. In particular, this implies that the root
         directory is always represented by the first record in the
         table, because it is the only directory with level 1.     (2) If the levels are identical, but the directories have different
         parents, then the directories are in the same relative
         positions as their parents.     (3) Directories with the same level and the same parent are
         arranged in the order obtained by sorting on their names, as
         described in Section 6.
A directory consists of a series of directory records in one or more
consecutive sectors. However, unlike path records, directory records may
not straddle sector boundaries. There may be unused space at the end of
each sector, which is filled with zeros.Each directory record represents a file or directory. Its format is as
follows:     length
     in bytes  contents
     --------  ---------------------------------------------------------
        1      R, the number of bytes in the record (which must be even)
        1      0 [number of sectors in extended attribute record]
        8      number of the first sector of file data or directory
                 (zero for an empty file), as a both endian double word
        8      number of bytes of file data or length of directory,
                 excluding the extended attribute record,
                 as a both endian double word
        1      number of years since 1900
        1      month, where 1=January, 2=February, etc.
        1      day of month, in the range from 1 to 31
        1      hour, in the range from 0 to 23
        1      minute, in the range from 0 to 59
        1      second, in the range from 0 to 59
                 (for DOS this is always an even number)
        1      offset from Greenwich Mean Time, in 15-minute intervals,
                 as a twos complement signed number, positive for time
                 zones east of Greenwich, and negative for time zones
                 west of Greenwich (DOS ignores this field)
        1      flags, with bits as follows:
                 bit     value
                 ------  ------------------------------------------
                 0 (LS)  0 for a norma1 file, 1 for a hidden file
                 1       0 for a file, 1 for a directory
                 2       0 [1 for an associated file]
                 3       0 [1 for record format specified]
                 4       0 [1 for permissions specified]
                 5       0
                 6       0
                 7 (MS)  0 [1 if not the final record for the file]
        1      0 [file unit size for an interleaved file]
        1      0 [interleave gap size for an interleaved file]
        4      1, as a both endian word [volume sequence number]
        1      N, the identifier length
        N      identifier
        P      padding byte: if N is even, P = 1 and this field contains
                 a zero; if N is odd, P = 0 and this field is omitted
    R-33-N-P   unspecified field for system use; must contain an even
                 number of bytesThe length of a directory includes the unused space, if any, at the ends
of sectors. Hence it is always an exact multiple of 2048 (the sector
size). Since every directory, even a nominally empty one, contains at
least two records, the length of a directory is never zero.All fields in the first record (sometimes called the "." record) refer
to the directory itself, except that the identifier length is 1, and the
identifier is zero. The root directory record in the Primary Volume
Descriptor also has this format.All fields in the second record (sometimes called the ".." record) refer
to the parent directory, except that the identifier length is 1, and the
identifier is 1. The second record in the root directory refers to the
root directory.The identifier for a subdirectory is its name. The identifier for a file
consists of the following fields, in the order given:     (1) The name, consisting of the ASCII codes for at least one and
         not more than eight capital letters, digits and underscores.     (2) If there is an extension, the ASCII code for a period (46). If
         there is no extension, this field is omitted.     (3) The extension, consisting of the ASCII codes for not more than
         three capital letters, digits and underscores. If there is no
         extension, this field is omitted.     (4) The ASCII code for a semicolon (59).     (5) The ASCII code for 1 (49). [On other systems, this is the
         version number, consisting of the ASCII codes for a sequence of
         digits representing a number between 1 and 32767, inclusive.]Some implementations for DOS omit (4) and (5), and some use punctuation
s other than underscores in file names and extensions.Directory records other than the first two are sorted as follows:     (1) Records are sorted by name, as described above.     (2) Every series of records with the same name is sorted by
         extension, as described above. For this purpose, a record
         without an extension is sorted as though its extension
         consisted of ASCII blanks (32).     (3) [On other systems, every series of records with the same name
         and extension is sorted in order of decreasing version number.]     (4) [On other systems, two records with the same name, extension
         and version number are permitted, if the first record is an
         associated file.][ISO9660 permits names containing more than eight characters and
extensions containing more than three characters, as long as both of
them together contain no more than 30 characters.]It is apparently permissible under ISO9660 to use two or more
consecutive records to represent consecutive pieces of the same file.
Bit 7 of the flags byte is set in every record except the last one.
However, this technique seems pointless and is apparently not used. It
is not supported by MSCDEX.Interleaving is another technique that is apparently seldom used. It is
not supported by MSCDEX (version 2.10).

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求解：iso文件路径表分析

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