Re: iSCSI - bookmarks change

[Mark Bakke <mbakke@cisco.com>]

Rod-

I like this solution; the intiator would still send a valid
ITT, but with one text command per connection, the target
could use either the ITT or the connection itself to find
the bookmark, whichever was more convenient.

Is there anyone out there that still wants more than one
outstanding text command on a connection?

--
Mark

Rod Harrison wrote:
> 
> Mark,
> 
>         If we do this it will require the initiator to do some
> special case handling of text responses. The Initiator Task
> Tag is the initiators only way of finding its data
> structures pertaining to the command, removing it will
> require the initiator to "know" about the location of the
> text command. This in itself is not terribly difficult, but
> it is a special case. I would prefer we leave the ITT where
> it is and allow initiators to use a common method for
> decoding responses. We can still mandate only one text
> command per connection.
> 
>         - Rod
> 
> -----Original Message-----
> From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On
> Behalf Of
> Mark Bakke
> Sent: Wednesday, September 05, 2001 4:30 PM
> To: Julian Satran
> Cc: ips@ece.cmu.edu
> Subject: Re: iSCSI - bookmarks change
> 
> Julian-
> 
> This is getting a lot simpler.  We can go even further by
> turning
> the SHOULD below into a MUST.
> 
> If we say:
> 
>    A connection MUST have only one outstanding text command
> at
>    any given time.
> 
> This means that the bookmark flag references the connection
> on
> which the text command is done, and makes the Initiator Task
> Tag unnecessary in both the text command and response.  We
> can
> turn these into reserve fields, and reference the connection
> instead of the ITT when discussing bookmarked commands.
> 
> --
> Mark
> 
> Julian Satran wrote:
> >
> > Now that text commands are out of login (and we don't have
> to care too much
> > about the immediate version) we can rationalize the
> bookmarks.
> >
> > Here is my suggestion for the new text request/response:
> >
> > 1.1  Text Command
> >
> >    The Text Command is provided to allow the exchange of
> information and
> >    for future extensions. It permits the initiator to
> inform a target of
> >    its capabilities or to request some special operations.
> >
> >    A connection SHOULD have only one outstanding text
> command at any given
> >    time.
> >
> >    Byte /    0       |       1       |       2       |
> 3       |
> >       /              |               |               |
> |
> >      |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6
> 5 4 3 2 1 0|
> >
> +---------------+---------------+---------------+-----------
> ----+
> >     0|X|I| 0x04      |F|B| Rsvd      | Reserved
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >     4| Reserved      | DataSegmentLength
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >     8| Reserved
> |
> >      +
> +
> >    12|
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    16| Initiator Task Tag
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    20| Reserved
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    24| CmdSN
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    28| ExpStatSN
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    32/ Reserved
> /
> >     +/
> /
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    48| Digests if any...
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >      / DataSegment (Text)
> /
> >     +/
> /
> >
> +---------------+---------------+---------------+-----------
> ----+
> >
> > 1.1.1     F (Final) Bit
> >
> >    When set to 1 it indicates that this is the last or
> only text command in
> >    a sequence of commands; otherwise it indicates that
> more commands will
> >    follow.
> >
> > 1.1.2     I - Immediate
> >
> >    During the Login Phase (the current stage part of CNxSG
> is either
> >    SecurityNegotiation or LoginOperationalNegotiation),
> the Text command
> >    SHOULD be issued as an immediate command (I=1).
> >
> > 1.1.3     B - bookmark bit
> >
> >    The bookmark bit set to 1 tells the target to continue
> from its last
> >    bookmark for the specific Initiator Task Tag and thus
> allows a target to
> >    transfer a large amount of textual data over a sequence
> of
> >    text-command/text-response exchanges.
> >
> >    The bookmark bit set to 0 tells the target that this is
> a new Text
> >    request; the target should reset any bookmark it holds
> on the specific
> >    Initiator Task Tag.
> >
> >    A target MAY reject an old Bookmark.
> >
> >    Bookmark generation at target is detailed in 2.11.2.
> >
> >    Long text responses are handled as in the following
> example:
> >
> >       I->T Text SendTargets=all (F=1,B=0)
> >       T->I Text <part 1> (F=0,B=1)
> >       I->T Text <empty> (F=1,B=1)
> >       T->I Text <part 2> (F=0,B=1)
> >       I->T Text <empty> (F=1,B=1)
> >       ...
> >       T->I Text <part n> (F=1,B=0)
> >
> > 1.1.4     Initiator Task Tag
> >
> >    The initiator assigned identifier for this Text
> Command.
> >    If the command is sent as part of a sequence of
> commands (e.g., the
> >    Login Phase or a sequence of Text commands) the
> Initiator Task Tag MUST
> >    be the same for all the commands within the sequence
> (similar to linked
> >    SCSI commands).
> >
> > 1.1.5     Text
> >
> >    The initiator sends the target a set of key=value or
> key=list pairs
> >    encoded in UTF-8 Unicode. All the text keys and text
> values specified in
> >    this document are to be presented and interpreted in
> the case they
> >    appear in this document (they are case sensitive). The
> key and value are
> >    separated by a '=' (0x3d) delimiter. Every key=value
> pair (including the
> >    last or only pair) MUST be followed by null (0x00)
> delimiter.  A list is
> >    a set of values separated by comma (0x2c). Large binary
> items can be
> >    encoded using their hexadecimal representation (e.g.,
> 8190 is 0x1ffe) or
> >    decimal representation. The maximum length of an
> individual value (not
> >    its string representation) is 255 bytes.
> >
> >    The data lengths of a text command or response MUST NOT
> exceed 4096
> >    bytes.  Key names MUST NOT exceed 63 bytes. Key values
> MUST NOT exceed
> >    255 bytes.
> >
> >    Character strings are represented as plain text.
> Numeric and binary
> >    values are represented using either decimal numbers or
> the hexadecimal
> >    0xffff notation. Upper and lower case letters may be
> used
> >    interchangeably in hexadecimal notation (i.e., 0x1aBc,
> 0x1AbC and 0x1ABC
> >    are equivalent).
> >
> >    The target responds by sending its response back to the
> initiator. The
> >    response text format is similar to the request text
> format.
> >
> >    Some basic key=value pairs are described in Appendix A
> and Appendix D.
> >    All keys in Appendix D, except for the X- extension
> format, MUST be
> >    supported by iSCSI initiators and targets. Keys in
> Appendix A MUST be
> >    supported only when the function they refer to is
> mandatory to
> >    implement.
> >
> >    Manufacturers may introduce new keys by prefixing them
> with X- followed
> >    by their (reversed) domain name, for example the
> company owning the
> >    domain acme.com can issue:
> >
> >       X-com.acme.bar.foo.do_something=0000000000000003
> >
> >    Any other key not understood by the target may be
> ignored by the target
> >    without affecting basic function. However the Text
> Response for a key
> >    that was not understood MUST be key=NotUnderstood.
> >
> >    Text operations are usually meant for parameter
> setting/negotiations but
> >    can be used also to perform some long lasting
> operations.
> >
> >    Text operations that will take a long time should be
> placed in their own
> >    Text command.
> >
> > 1.2
> >
> > Text Response
> >
> >    The Text Response PDU contains the target's responses
> to the initiator's
> >    Text Command. The format of the Text field matches that
> of the Text
> >    Command.
> >
> >    Byte /    0       |       1       |       2       |
> 3       |
> >       /              |               |               |
> |
> >      |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6
> 5 4 3 2 1 0|
> >
> +---------------+---------------+---------------+-----------
> ----+
> >     0|1|1| 0x24      |F|B| Rsvd      | Reserved
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >     4| Reserved      | DataSegmentLength
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >     8| Reserved
> |
> >      +
> +
> >    12|
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    16| Initiator Task Tag
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    20| Reserved
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    24| StatSN
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    28| ExpCmdSN
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    32| MaxCmdSN
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    36/ Reserved
> /
> >     +/
> /
> >
> +---------------+---------------+---------------+-----------
> ----+
> >    48| Digests if any...
> |
> >
> +---------------+---------------+---------------+-----------
> ----+
> >      / DataSegment (Text)
> /
> >     +/
> /
> >
> +---------------+---------------+---------------+-----------
> ----+
> >
> > 1.2.1     F (Final) Bit
> >
> >    When set to 1 in response to a text command with the
> Final bit set to 1
> >    the F bit indicates that the target has finished the
> current stage of
> >    the operation or the whole operation.  Otherwise if set
> to 0 in response
> >    to a text command with the Final Bit set to 1 it
> indicates that the
> >    target has more work to do (invites a follow-on text
> command).  A text
> >    response with the F bit set to 1 in response to a text
> command with the
> >    F bit set to 0 is a protocol error.
> >
> >    A text response with a F bit set to 1 MUST NOT contain
> key=value pairs
> >    that may require additional answers from the initiator.
> >
> > 1.2.2     B - bookmark Bit
> >
> >    Whenever a target can't transfer all the remaining text
> data in a single
> >    Text response, it attempts to set an internal bookmark.
> If successful,
> >    the target associates the bookmark with the Initiator
> Task Tag.  The
> >    target indicates that it holds a bookmark for the
> specific Initiator
> >    Task Tag by setting the bookmark (B) bit to 1 in the
> Text response. The
> >    target resets the internal bookmark associated with a
> given Initiator
> >    Task Tag if it receives a Text request with the
> specified Initiator Task
> >    Tag with the bookmark bit set to 0.  When a target
> can't transfer all
> >    the text data in a single text response and it cannot
> set an internal
> >    bookmark it rejects the Text request with an
> appropriate Reject code. A
> >    target may reset its internal bookmark(s) after some
> time in order to
> >    reclaim resources associated with the bookmark and
> reject subsequent
> >    Text requests with the bookmark bit set to 1.
> >
> >    When all the text data fit in a single Text response
> the bookmark bit of
> >    the response is set to 0 and the bookmark associated
> with the Initiator
> >    Task Tag is reset.
> >
> > 1.2.3     Initiator Task Tag
> >
> >    The Initiator Task Tag matches the tag used in the
> initial Text Command
> >    or the Login Initiator Task Tag.
> >
> > 1.2.4     Text Response Data
> >
> >    The Text Response Data Segment contains responses in
> the same key=value
> >    format as the Text Command and with the same length and
> coding
> >    constraints. Appendix A and Appendix D lists some basic
> Text Commands
> >    and their Responses.
> >
> >    Although the initiator is the requesting party and
> controls the
> >    request-response initiation and termination the target
> can offer
> >    key=value pairs of its own as part of a sequence and
> not only in
> >    response to an identical key=value pair offered by the
> initiator.
> >
> >    A Key=value pair must be confined to a given text
> response even in the
> >    presence of bookmark - i.e., it must start and end
> within one Text
> >    Response.
> >
> > The Reject Reasons table looks like:
> >
> > 1.1.1     Reason
> >
> >    The reject Reason is coded as follows:
> >
> >
> +------+-----------------------------------------+----------
> --------+
> >    | Code | Explanation                             | Can
> the original |
> >    | (hex)|                                         | PDU
> be re-sent?  |
> >
> +------+-----------------------------------------+----------
> --------+
> >    | 0x01 | Format Error                            | no
> |
> >    |      |                                         |
> |
> >    | 0x02 | Data (payload) Digest Error             | yes
> (Note 1)    |
> >    |      |                                         |
> |
> >    | 0x03 | Data-SNACK Reject                       | yes
> |
> >    |      |                                         |
> |
> >    | 0x04 | Protocol Error (e.g., SNACK request for | no
> |
> >    |      | a status that was already acknowledged) |
> |
> >    |      |                                         |
> |
> >    | 0x05 | Command not supported in this session   | no
> |
> >    |      | type                                    |
> |
> >    |      |                                         |
> |
> >    | 0x06 | Immediate Command Reject - too many     | yes
> |
> >    |      | immediate commands                      |
> |
> >    |      |                                         |
> |
> >    | 0x07 | Bookmark Reject - No bookmark for this  | no
> |
> >    |      | Initiator Task Tag                      |
> |
> >    |      |                                         |
> |
> >    | 0x08 | Bookmark Reject - Can't generate        | yes
> |
> >    |      | bookmark - out of resources             |
> |
> >    |      |                                         |
> |
> >    | 0x0f | Full Feature Phase Command before login | no
> |
> >
> +------+-----------------------------------------+----------
> --------+
> >
> >  Comments?
> >
> >  Julo
> 
> --
> Mark A. Bakke
> Cisco Systems
> mbakke@cisco.com
> 763.398.1054

-- 
Mark A. Bakke
Cisco Systems
mbakke@cisco.com
763.398.1054