scsi-disk: respect the page control (PC) field in the MODE SENSE command
The page control (PC) field defines the type of mode parameter values to be returned in the mode pages: PC=0 : Current values PC=1 : Changeable values PC=2 : Default values PC=3 : Saved values The current implementation always returns the same type of parameters. This is OK for Current and Default values as we don't support changes to be done by the MODE SELECT command. For Saved values the following applies (implemented by this patch): "A PC field value of 3h requests that the target return the saved values of the mode parameters. Implementation of saved page parameters is optional. Mode parameters not supported by the target shall be set to zero. If saved values are not implemented, the command shall be terminated with CHECK CONDITION status, the sense key set to ILLEGAL REQUEST and the additional sense code set to SAVING PARAMETERS NOT SUPPORTED." For Changeable values the following applies (implemented by this patch): "A PC field value of 1h requests that the target return a mask denoting those mode parameters that are changeable. In the mask, the fields of the mode parameters that are changeable shall be set to all one bits and the fields of the mode parameters that are non-changeable (i.e. defined by the target) shall be set to all zero bits." In newer versions of the SCSI-2 spec the following clause was added. "If the logical unit does not implement changeable parameters mode pages and the device server receives a MODE SENSE command with 01b in the PC field, then the command shall be terminated with CHECK CONDITION status, with the sense key set to ILLEGAL REQUEST, and the additional sense code set to INVALID FIELD IN CDB." This was not yet included in the SCSI-2 Working Drafts from 1986-1993. I assume that the variant to return CHECK CONDITION for PC=1 is not widely implemented by real devices. I have a legacy OS which fails, if MODE_SENSE returns non GOOD for PC=1. So for highest compatibility I implemented the former variant with this patch. The last Working Draft X3T9.2 Rev. 10L 7-SEP-93 can be found here: http://ldkelley.com/SCSI2/SCSI2/SCSI2-08.html#8.2.10 In mode_sense_page() this patch also avoids multiple hard coded definitions of the same mode page length. Instead I use the varable p[1]. In fact the returned length of the mode pages 4 and 5 were wrong (2 bytes less). Signed-off-by: NBernhard Kohl <bernhard.kohl@nsn.com> Signed-off-by: NKevin Wolf <kwolf@redhat.com> (cherry picked from commit 282ab04e)
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