What's the difference between sc_data_direction and sr_data_direction?
Matt Dharm
On Sun, 16 Apr 2000, Douglas Gilbert wrote:
> Oliver Neukum wrote:
> >
> > Hi,
> >
> > this may be a stupid question, but ...
> >
> > How is a driver who has gotten a *Scsi_Cmnd supposed to know whether the
> > data is to be read or written ?
>
> Well it's a good question. In the 2.3 series of development kernels
> a flag was added just for this purpose:
>
> /*
> * These are the values that the SCpnt->sc_data_direction and
> * SRpnt->sr_data_direction can take. These need to be set
> * The SCSI_DATA_UNKNOWN value is essentially the default.
> * In the event that the command creator didn't bother to
> * set a value, you will see SCSI_DATA_UNKNOWN.
> */
> #define SCSI_DATA_UNKNOWN 0
> #define SCSI_DATA_WRITE 1
> #define SCSI_DATA_READ 2
> #define SCSI_DATA_NONE 3
>
>
> So in the lk 2.2 series a driver must either guess on the basis
> of the SCSI opcode (probably not a good idea given non-standard
> opcodes) or be prepared for a data transfer in either direction.
> A combination of both policies may be useful (e.g. if the opcode
> is READ(6), READ(10) or READ(12) then ...).
>
> Doug Gilbert
>
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