SCSI-2

8.2.6 LOG SELECT command

The LOG SELECT command (see table 49) provides a means for the initiator to manage statistical information maintained by the device about the device or its logical units. Targets that implement the LOG SELECT command shall also implement the LOG SENSE command. Structures in the form of log parameters within log pages are defined as a way to manage the log data. The LOG SELECT command provides for sending zero or more log pages during a DATA OUT phase. This International Standard defines the format of the log pages, but does not define the exact conditions and events that are logged.

Table 49 - LOG SELECT command

===============================================================================
|  Bit|   7    |   6    |   5    |   4    |   3    |   2    |   1    |   0    |
|Byte |        |        |        |        |        |        |        |        |
|=============================================================================|
| 0   |                           Operation code (4Ch)                        |
|-----------------------------------------------------------------------------|
| 1   | Logical unit number      |              Reserved    |  PCR   |   SP   |
|-----------------------------------------------------------------------------|
| 2   |        PC       |         Reserved                                    |
|-----------------------------------------------------------------------------|
| 3   |                           Reserved                                    |
|-----------------------------------------------------------------------------|
| 4   |                           Reserved                                    |
|-----------------------------------------------------------------------------|
| 5   |                           Reserved                                    |
|-----------------------------------------------------------------------------|
| 6   |                           Reserved                                    |
|-----------------------------------------------------------------------------|
| 7   | (MSB)                                                                 |
|---------                        Parameter list length                    ---|
| 8   |                                                                 (LSB) |
|-----------------------------------------------------------------------------|
| 9   |                           Control                                     |
===============================================================================

A parameter code reset (PCR) bit of one and a parameter list length of zero shall cause all implemented parameters to be set to the target-defined default values (e.g. zero). If the PCR bit is one and the parameter list length is greater than zero, the command is terminated with CHECK CONDITION status. The sense key shall be set to ILLEGAL REQUEST and the additional sense code shall be set to INVALID FIELD IN CDB. A PCR bit of zero specifies that the log parameters shall not be reset.

A save parameters (SP) bit of one indicates that after performing the specified LOG SELECT operation the target shall save to non-volatile memory all parameters identified as savable by the DS bit in the log page (see 8.3.2). A SP bit of zero specifies that parameters shall not be saved.

Saving of log parameters is optional and indicated for each log parameter by the DS bit in the page. Log parameters may be saved at vendor-specific times subject to the TSD bit (see 8.3.2) in the log parameter. If the target does not implement saved parameters for any log parameter and the SP bit is set to one, the command shall be terminated with CHECK CONDITION status. The sense key shall be set to ILLEGAL REQUEST, and the additional sense code set to INVALID FIELD IN CDB.

It is not an error to set the SP bit to one and to set the DS bit of a log parameter to one. In this case, the parameter value for that log parameter is not saved.

The page control (PC) field defines the type of parameter values to be selected. The page control field is defined in table 50.

Table 50 - Page control field

   =======================================================================
   | Type  |  LOG SELECT parameter values |  LOG SENSE parameter values  |
   |---------------------------------------------------------------------|
   |  00b  |  Current threshold values    |  Threshold values            |
   |  01b  |  Current cumulative values   |  Cumulative values           |
   |  10b  |  Default threshold values    |  Default threshold values    |
   |  11b  |  Default cumulative values   |  Default cumulative values   |
   =======================================================================

The current cumulative values may be updated by the target or by the initiator using the LOG SELECT command to reflect the cumulative number of events experienced by the target. Fields in the parameter control byte (8.3.2) of each log parameter control the updating and saving of the current cumulative parameters.

The target shall set the current threshold parameters to the default threshold values in response to a LOG SELECT command with the PC field set to 10b and the parameter list length field set to zero.

The target shall set all cumulative parameters to their default values in response to a LOG SELECT command with the PC field set to 11b and the parameter list length field set to zero.

The current threshold value can only be modified by the initiator via the LOG SELECT command. If the initiator attempts to change current threshold values that are not available or not implemented for that log parameter, then the target shall terminate the LOG SELECT command with CHECK CONDITION status, the sense key set to ILLEGAL REQUEST, and the additional sense code set to INVALID FIELD IN PARAMETER LIST. The saving of current threshold parameters and the criteria for the current threshold being met are controlled by bits in the parameter control byte (8.3.2).

( Pages or log parameters that are not available may become available at some later time (e.g. after the device has become ready). )

The parameter list length field specifies the length in bytes of the parameter list that shall be transferred from the initiator to the target during the DATA OUT phase. A parameter list length of zero indicates that no pages shall be transferred. This condition shall not be considered an error. If the initiator sends page codes or parameter codes within the parameter list that are reserved or not implemented by the target, the target shall terminate the LOG SELECT command with CHECK CONDITION status. The sense key shall be set to ILLEGAL REQUEST and the additional sense code set to INVALID FIELD IN PARAMETER LIST.

If a parameter list length results in the truncation of any log parameter, the target shall terminate the command with CHECK CONDITION status. The sense key shall be set to ILLEGAL REQUEST and the additional sense code set to INVALID FIELD IN CDB.

The initiator should send pages in ascending order by page code value if multiple pages are sent during a DATA OUT phase. If multiple log parameters within a page are sent during the DATA OUT phase, they should be sent in ascending order by parameter code value. The target shall return CHECK CONDITION status if the initiator sends pages out of order or parameter codes out of order. The sense key shall be set to ILLEGAL REQUEST and the additional sense code set to INVALID FIELD IN PARAMETER LIST.

( Initiators should issue LOG SENSE commands prior to issuing LOG SELECT commands to determine supported pages and page lengths. )

The target may provide independent sets of log parameters for each logical unit or for each combination of logical units and initiators. If the target does not support independent sets of log parameters and any log parameters are changed that affect other initiators, then the target shall generate a unit attention condition for all initiators except the one that issued the LOG SELECT command (see 7.9). This unit attention condition is returned with an additional sense code of LOG PARAMETERS CHANGED.

If the initiator sends a log parameter that is not supported by the target, the target shall terminate the command with CHECK CONDITION status, set the sense key to ILLEGAL REQUEST, and set the additional sense code to INVALID FIELD IN PARAMETER LIST.