Re: iSCSI - bookmarks change

["Julian Satran" <Julian_Satran@il.ibm.com>]

Mark,

I gave it some tought.  Relating it to the connection and task makes for a
more difficult implementation.
You have to make available structures per connection and you can never then
relax the one-text-command per connection (now it is only a resource
statement more than a logical constraint).

The ITT allegiance is simple and it lets you store the local bookmark in a
data structure that will time-out.
I assume that a simple implementation will have one such
structure/initiator.

Regards,
Julo



Mark Bakke <mbakke@cisco.com>@cisco.com on 05-09-2001 18:29:49

Please respond to Mark Bakke <mbakke@cisco.com>

Sent by:  mbakke@cisco.com


To:   Julian Satran/Haifa/IBM@IBMIL
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