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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] iSCSI - bookmarks change
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
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