# Re: reaction to a smaller buffer size

From: Oliver Neukum (Oliver.Neukum@lrz.uni-muenchen.de)
Date: Sun Nov 19 2000 - 10:07:10 PST

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  > The problem is that a backend may consider sanei_scsi_max_request_size
  > as a constant. This was true for the old Linux SG driver; but with the
  > new SG driver it is at least in theory possible that you get different
  > buffer sizes each time a SG device file is opened. (Not very likely, but
  > it is possible)

  It's virtually certain if you have two host adapters, whose drivers differ
  in their ability to do scatter/gather. This means that SANE will always
  fail in that setup.

  > Both situations might have caused unnecessary work and headaches for
  > backend developers, who don't need or don't want to switch to
  > sanei_scsi_open_extended, and therefore I decided to use this "paranoid"
  > looking "if (real_buffersize != wanted_buffersize)", when I introduced
  > sane_scsi_open_extended and related stuff.

  I see, but in the case I mentioned above the user needs to limit the
  buffer by setting enviromental variables.

  > > Why don't you use sanei_scsi_open_extended if it is available for your
  > > paltform? In this case the backend can try to get a big buffer and
  > > knows the actual size it is allowed to use.

  I am using an existing backend (microtek2). It works with this check removed.
  Is converting a backend to use sanei_scsi_open_extended difficult ?

  Regards
  Oliver

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