The attachment is for discussion. It adds MODE SELECT
support to libata allowing the write(back) cache and
read ahead to be manipulated by users [i.e. the WCE and
DRA **  bits in the SCSI Caching mode page].

The patch is against lk 2.6.13-rc6 and includes the
SSU patch (but not the TUR patch).

It highlights several issues with libata:
   - may need hook so SCSI command specific logic can be
     executed _after_ a ATA command has completed successfully
   - one SCSI command can map to two or more
     ATA commands (e.g. a MODE SELECT caching
     page that changes the state of both WCE and DRA)
     I cannot see a graceful way to do this with libata.
   - patch generalizes error processing but probably
     not enough
   - may need lighter weight version of
     ata_dev_identify() when the "dev->id" array needs
     to be resync-ed (e.g. as required by the ATA information
     VPD page in sat-r05)

ChangeLog:
   - generalize SCSI error processing
   - add MODE SELECT (6 and 10) handling; active for
     WCE and DRA in Caching mode page
   - add block descriptor to MODE SENSE command
   - make various changes to sync with sat-r05 (as
     noted in source)
   - answer some "FIXME" questions in code and flag
     points for extra work


** Testing this patch highlighted a bug in sdparm effecting
   DRA (but not WCE). A beta version of sdparm-0.95 can be
   found at http://www.torque.net/sg/sdparm.html that fixes
   the problem.


Not to be applied to mainline kernel yet.

Doug Gilbert