iSCSI: Marker negotiation - draft 11

[Michael Schoberg <michael_schoberg@cnt.com>]

Title:

   A.2  Initial Marker-less Interval

 

           To enable the connection setup including the login phase negotiation,
           marking (if any) is started only at the first marker interval after
           the end of the login phase. However, in order to enable the marker
           inclusion and exclusion mechanism to work without knowledge of the
           length of the login phase, the first marker will be placed in the TCP
           stream as if the Marker-less interval had included markers.

 

           Thus all markers appear in the stream at locations conforming to the
           formula: [(MI + 8) * n - 8] where MI = Marker Interval, n = integer
           number.

 

           As an example if the marker interval is 512 and the login ended at
           byte 1003 (first iSCSI placed byte is 0) the first marker will be
           inserted after byte 1031 in the stream.

 

 

The formula doesn't make sense to me.  An interval of 512 = 2048 bytes.  Wouldn't the first marker would be placed around byte 2048 instead of 1032?

 

A.3.2   OFMarkInt, IFMarkInt

 

           Use: IO
           Senders: Initiator and Target
           Scope: CO

 

           Offering:

 

           OFMarkInt=<integer-from-1-to-65535>[,<integer-from-1-to-65535>]
           IFMarkInt=<integer-from-1-to-65535>[,<integer-from-1-to-65535>]

 

           Responding:

 

           OFMarkInt=<integer-from-1-to-65535>|Reject
           IFMarkInt=<integer-from-1-to-65535>|Reject

 

           OFMarkInt is used to set the interval for the initiator to target
           markers on the connection.  IFMarkInt is used to set the interval for
           the target to initiator markers on the connection.

 

           For the offering the initiator or target indicates the minimum to max-
           imum interval (in 4-byte words) it wants the markers for one or both
           directions. In case it only wants a specific value, only a single
           value has to be specified. The responder selects a value within the
           minimum and maximum offered or the only value offered or indicates
           through the xFMarker key=value its inability to set and/or receive
           markers. When the interval is unacceptable the responder answers with
           "Reject".  Reject is resetting the marker function in the specified
           direction (Output or Input) to No.

 

           The interval is measured from the end of a marker to the beginning of
           the next marker. For example, a value of 1024 means 1024 words (4096
           bytes of iSCSI payload between markers).

 

           The default is 2048.

 

Why allow for intervals as small as 4-bytes on markers?  Is a range of values really necessary?

 

I: OFMarker=yes | IFMarker=yes | OFMarkInt=1,512 | IFMarkInt=1,512
T: OFMarker=yes | IFMarker=yes | OFMarkInt=1 | IFMarkInt=1

 

(BTW: Why was the above naming chosen over: ITMarker, TIMarker, ITMarkInt, TIMarkInt.  OF & IF prefixes don't seem intuitively perspective-obvious.)

 

Instead of offering a range (which seems kind of unnecessary), how about offering only the value the entity wishes to receive?  Example:

 

I: TIMarker=yes | TIMarkInt=512 | ITMarker=yes | ITMarkInt=0
T: TIMarker=yes | TIMarkInt=512 | ITMarker=yes | ITMarkInt=2048

The draft says "Default is 2048", how does that get negotiated?

 

I: OFMarker=yes | IFMarker=yes
T: OFMarker=yes | IFMarker=yes

 

Will the above negotiate the default OF & IF Marker Intervals?

 

Also, section 9.10.4 does not explicitly say that only a parameter negotiated by the initiator may be returned in a target's response.  So would this be possible?

 

I: OFMarker=yes | IFMarker=yes | OFMarkInt=1,512
T: OFMarker=yes | IFMarker=yes | OFMarkInt=1 | IFMarkInt=1