[T10] Can application clients use the DS bit force device servers not to save log parameter values?

Ralph Weber Ralph.Weber at wdc.com
Tue Oct 19 08:14:20 PDT 2021

In 05-242r2<https://www.t10.org/cgi-bin/ac.pl?t=d&f=05-242r2.pdf>, the DS (Disable Save) bit moved from the log parameter control byte to byte 0 of the Log Page format, but...

The DS bit also underwent an "interesting" change in meaning.

  *   [before 05-242r2] - "A DS bit set to one indicates that the logical unit does not support saving that log parameter in response to a LOG SELECT or LOG SENSE command with an SP bit set to one."
  *   [after 05-242r2] - "The disable save (DS) bit operates in conjunction with the PCR bit, the SP bit, and the PARAMETER LIST LENGTH FIELD in the LOG SELECT CDB (see 6.4). Table 5 defines the meaning for all of the combinations of values for the PCR bit, the SP bit, and the DS bit when the PARAMETER LIST LENGTH FIELD contains a value greater than 0000h (i.e., parameter data is being sent with the LOG SELECT command)."

The [after 05-242r2] wording seems less malicious, when the proposal's title is considered, "Combinations of bits and fields in the LOG SELECT CDB and log parameters", but fresh eyes are wondering if the appropriate intent was to maintain the original "what the logical unit allows" wording along with clarifying the actions of bit/field combinations.

Please speak up, if something important appears to have been lost in the 05-242r2 changes.

FWIW One suggestion for restoring the pre-05-242r2 intent would be to add something along the lines of the following to SPC-6...

<begin possible new text>
For any specific combination of page code, subpage code, and page control (PC) (see  6.8), a DS bit that has a different value in parameter data specified by the application client than in parameter data indicated by the device server may result in the device server:

  1.  ignoring the DS bit in the parameter data specified by the application client, or
  2.  terminating the command with CHECK CONDITION status, with the sense key set to ILLEGAL REQUEST, and the additional sense code set to INVALID FIELD IN PARAMETER LIST.
<end possible new text>

In order to accommodate existing products, the proposal text must include a wide variety of device server actions.

All the best,
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