rfc122.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   Each of the fields 'FILENAME','ACCESS PASSWORD', 'MODIFICATION
   PASSWORD', and 'NEW FILENAME' is further divided into the following
   subfields:

      8         8*LENGTH
   ________________________//___
  |        |                    |
  | LENGTH | FILENAME/PASSWORD  |
  |________|_______________//___|


   where the 'LENGTH' subfield contains the length in 8-bit characters
   of the 'FILENAME/PASSWORD' subfield.

   This is the _general_ format for all SMFS commands.  No one command
   type requires all of the fields specified above.  A particular subset
   of these fields is defined for each type of command, and only those
   fields should appear.  The defined fields for each command type are
   indicated in Figure 3.

   Furthermore, not all of the fields which are defined for a particular
   command type need always appear _explicitly_.  The user should
   envision that SMFS maintains filename, password, and bit-count
   accumulators.  Every time a filename (or new filename),



J. White                                                       [Page 11]

RFC 122                Simple-Minded file System              April 1971


   access/modification password, or bit count appears explicitly in the
   input stream, it is saved in the appropriate accumulator (a null
   password -- designated by setting Bits 0,3 or Bits 8,11 to zero
   (Figure 4) -- should be thought of as appearing explicitly).  The
   user may cause a defined field to _default_ to the current contents
   of the appropriate accumulator by turning on the appropriate bin in
   the flags field (see Figure 4).  When a field defaults in this
   manner, that field is said to appear _implicitly_ in the command.

         NOP                        0                 No operation.

         FNO                        1                 File no operation.

         ALF                        2                 Allocate file.

         UDF                        3                 Update File.

         RPF                        4                 Replace File.

         RTF                        5                 Retrieve File.

         SPF                        6                 Space File.

         DLF                        7                 Delete File.

         RNF                        8                 Rename File.

                                Figure 2
                             Command Op codes

   The three accumulators are initially empty and hence an attempt to
   default a field in the first command in the input stream illicits an
   error indication.  A field of the appropriate type must appear once
   explicitly in the input stream before the corresponding accumulator
   is considered defined.  Furthermore, whenever SMFS detects an invalid
   filename or password (i.e., improper length or deviation from the
   character set) in the input stream, the appropriate accumulator is
   left empty again.

   SMFS allows operations on several files to be interleaved in the
   input stream by including in its command formats provision for
   explicitly specifying filename and password information in each
   command.  When many operations involving the same file appear
   sequentially in the input stream, the user need only let the
   appropriate fields default in all but the first command, avoiding
   re-transmission of what would otherwise be redundant parameters.





J. White                                                       [Page 12]

RFC 122                Simple-Minded file System              April 1971


                                          M
                                          O
                                          D
                                          I
                                          F
                                          I
                                  A       C
                                  C       A
                                  C       T
                                  E       I      N
                                  S       O      E
                                  S       N      W
                                                       B
                            F     P       P      F     I
            O               I     A       A      I     T
            P               L     S       S      L
                    F       E     S       S      E     C
            C       L       N     W       W      N     O     D
            O       A       A     O       O      A     U     A
            D       G       M     R       R      M     N     T
            E       S       E     D       D      E     T     A
   _____________________________________________________________
   ALF      X       X       X     X       X            X
   _____________________________________________________________
   UDF      X       X       X             X            X     X
   _____________________________________________________________
   RPF      X       X       X             X            X     X
   _____________________________________________________________
   RTF      X       X       X     X                    X
   _____________________________________________________________
   SPF      X       X       X     X                    X
   _____________________________________________________________
   DLF      X       X       X             X
   _____________________________________________________________
   RNF      X       X       X             X      X
   _____________________________________________________________
   FNO      X
   _____________________________________________________________
   NOP      X
   _____________________________________________________________


                               Figure 3

                         Defined Command Fields

        Note: Command fields marked with an 'X' are defined.




J. White                                                       [Page 13]

RFC 122                Simple-Minded file System              April 1971


   0   ACCESS PASSWORD        The access password for this
       DEFAULTS               operation defaults to the access
                              or modification password which
                              appeared explicitly most
                              recently in the input stream;
                              hence, it does not appear
                              explicitly in the current
                              command.

   1   BIT COUNT DEFAULTS     The bit count for this operation
                              defaults to that which appeared
                              explicitly most recently in the
                              input stream; hence it does not
                              appear explicitly in the current
                              command.

   2   FILENAME DEFAULTS      The filename for this operation
                              defaults to the filename or new
                              filename which appeared explicitly
                              most recently in the input stream;
                              hence it does not appear
                              explicitly in the current command.

   3   ACCESS PASSWORD        The access password for this
       APPEARS EXPLICITLY     operation appears explicitly in
                              the current command. (Bits 0,
                              3 = 0 indicates that no access
                              password was/is-to-be defined
                              for the file.)

   4   ECHO OP CODE           SMFS shall echo the op code and
       AND FILENAME           filename (whether it appears
                              explicitly or not) by copying
                              them into the output stream
                              ahead of any other response to
                              the current command.

   5-7 undefined              Not examined; should be zeros.

   8   MODIFICATION           Same as Bit 0, but applied to
       PASSWORD DEFAULTS      the modification password, rather
                              than the access password.

                         Figure 4

              Definition of Command FLAGS Bits





J. White                                                       [Page 14]

RFC 122                Simple-Minded file System              April 1971


   9   FILE FORMATTED         FOR UDF/RTF: this segment is part
                              of a formatted file; hence SMFS
                              should record the bit count. For
                              RTF/SPF: the referenced file is
                              formatted; hence the bit count
                              does not appear explicitly in the
                              current command

   10   NEW FILENAME          same as Bit 2, but applied
        DEFAULTS              to the new filename, rather
                              than the filename.

   11   MODIFICATION PASSWORD Same as Bit 3, but applied to
        APPEARS EXPLICITLY    the modification password,
                              rather than the access
                              password.

   12-15 undefined            Not examined; should be zeros.

                      Figure 4(continued)

                 Definition of Command FLAGS Bits

      Note: The sixteen bits of FLAGS are numbered 0-15 from
         left to right.

   When a series of RTF/SPF operations referencing the same file are
   juxtaposed in the input stream (as discussed in Section V.D.), they
   cause successive segments of the file to be transmitted _only_ if
   both filename and access password default (Bits 0,2 = 1) (a null
   password is also acceptable) in those operations following the first
   in the series.  If the user specifies either parameter explicitly in
   a command in the series -- even if the explicitly stated value is the
   same as what would have been the default value -- SMFS considers the
   series terminated, as if a FNO had been encountered, and hence the
   command in question returns, or flushes, the first segment of the
   file.  Allowing both filename and password to default has the added
   effect, in both RTF/SPF and UDF series, of decreasing the processing
   time required by SMFS to execute the operations which comprise the
   series.  Under such circumstances, SMFS executes such initial
   functions as file location and password verification only once at the
   beginning of the series, rather than for each operation.  Hence, a
   potential for increased transmission rates exists.  Furthermore, in
   such a series of UDF/RPF operations, SMFS is able to conserve
   secondary storage by concatenating file segments before they are
   written out.





J. White                                                       [Page 15]

RFC 122                Simple-Minded file System              April 1971


   Whenever SMFS aborts the processing of a command in the input stream
   (e.g., the filename is invalid, an incorrect password is supplied,
   etc), SMFS flushes the entire command.  Suppose, for example, that
   the file specified in a UDF operation does not exist (i.e., has not
   been allocated).  If the data field for the operation is very long,
   SMFS may well detect the non-existence of the file before the data
   field has been transmitted by the user.  In such cases, SMFS will
   accept and flush whatever remains of the aborted command (in this
   case, including the very long data field) until it reaches the point
   in the input stream at which it expects to find the next command,
   which it will process normally.  SMFS will, however, notify the user
   that the command was aborted by placing an appropriate indicator in
   the output stream, and it will do this as soon as it detects the
   error (and hence, in this case, before the erroneous command has been
   flushed from the input stream).  Hence, the user has the option of
   aborting the process by closing the connection.

   SMFS considers a command with an invalid op code as an especially
   severe error, since it has no way of locating the start of the next
   command.  Accordingly, it places a special character (X'FF') in the
   output stream, follows it with the invalid op code, and then closes
   its connections to the user.

VII.  Output Stream Format

   SMFS will respond to each command it extracts from the input stream
   -- every command except FNO and NOP -- by placing a command response
   in the output stream.  Command responses have the following general
   format:

       8                8       32
     _________//___________________________//____
    | OP  |          | CMPL |         |          |
    |CODE | FILENAME | CODE |BIT COUNT|  DATA    |
    |_____|___//_____|______|_________|____//____|

   where the lengths of fixed-length fields have been indicated in bits.
   The field 'FILENAME' is further divided into the following subfields: