# Re: Problem with kernel 2.4ac9, ava1505, snapscan1236s, sane1.0.4

From: Erik Inge Bolsų (knan@mo.himolde.no)
Date: Sun Jan 14 2001 - 12:31:19 PST

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  On Sun, 14 Jan 2001, Douglas Gilbert wrote:
  >This is interesting. The linux scsi subsystem (as does
  >FreeBSD's CAM) implements "autosense" to get its sense
  >buffer after a command has failed. This means that when
  >a command like "test unit ready" is sent and it returns
  >a "check condition" status code then the subsystem will
  >automatically issue a "request sense" and give its
  >response back as the sense buffer of the original command
  >("test unit ready" in this case).
  >
  >So SANE backends shouldn't be issuing "request sense"
  >commands IMHO. BTW only the first "request sense" gets
  >the error response, so sending more of them is useless.

  Hmm, interesting.

  Did a grep in current sources, and found that 12 out of 30-something
  backends issue request_sense commands currently.

  But a problem is: what about the other OS'es supported by
  SANE? AIX, Unixware, OS/2, HP-UX, Solaris, *BSD ? I expect not all of
  these use the "autosense" method... And that's probably why these backends
  issue request_sense commands.

  So do we need to implement some sort of: (pseudocode following)

  error = do_scsi_command(cmd);
  if ((error < 0) && OS_AUTOSENSE)
  sense = cmd->sense;
  else
  sense = do_scsi_command(request_sense);

  in some generic layer somewhere?

  I'm not familiar with SANE internals, so this might already exist, for all
  I know :)

  >It seems as though a problem that Arnold Schiller has
  >sent me is very similar: a SnapScan1236/aha152x
  >combination that locks up just after a "request sense"
  >is sent to the scanner.

  Sounds like the same problem, indeed.

      --
      Erik I. Bolsų | email: <knan at mo.himolde.no>
      The UNIX philosophy basically involves giving you enough rope to
      hang yourself.  And then a couple of feet more, just to be sure.
      --
      Source code, list archive, and docs: http://www.mostang.com/sane/
      To unsubscribe: echo unsubscribe sane-devel | mail majordomo@mostang.com

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