[7204] in linux-scsi channel archive
Re: Fixing SCSI Layer
daemon@ATHENA.MIT.EDU (Tony Chung)
Fri Sep 10 16:29:09 1999
Date: Fri, 10 Sep 1999 13:10:08 -0700
From: Tony Chung <chungto@ampex.com>
To: "Kenneth D. Merry" <ken@kdm.org>
CC: linux-scsi@vger.rutgers.edu
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"Kenneth D. Merry" wrote:
> Tony Chung wrote...
> >
> >
> > >
> > > 1 - Add a 'direction' field to the scsi command structure that can be
> > > filled with the following values:
> > > DIR_INPUT, DIR_OUTPUT, DIR_NONE and DIR_UNKNOWN=0
> > > Set this field to DIR_UNKNOWN=0 by default.
> > >
> >
> > >From Digital Unix /usr/include/io/cam.h:
> >
> > /* Defines for the CAM flags field in the CCB header. */
> >
> > #define CAM_DIR_RESV 0x00000000 /* Data direction (00: reserved) */
> > #define CAM_DIR_IN 0x00000040 /* Data direction (01: DATA IN) */
> > #define CAM_DIR_OUT 0x00000080 /* Data direction (10: DATA OUT) */
> > #define CAM_DIR_NONE 0x000000C0 /* Data direction (11: no data) */
> >
> > While UDI scsi spec has:
> > #define UDI_SCSI_DATA_IN (1U<<0)
> > #define UDI_SCSI_DATA_OUT (1U<<1)
> >
> > Basically, it can't be UNKNOWN because the Peripheral Driver must specify the
> > buffer address and total transfer size. Any inconsistencies should return error
> >
> > or let the host adaptor card simply return data overrun or data underrun.
> >
> >
> > I found CAM_DIR_NONE is potential hazard because
> > if some one specify CAM_DIR_NONE, another person
> > may mistakenly check for:
> > If (flags & CAM_DIR_OUT) ...../* condition true and do something wrong
> > */
>
> In FreeBSD/CAM, we added a mask:
>
> CAM_DIR_RESV = 0x00000000,/* Data direction (00:reserved) */
> CAM_DIR_IN = 0x00000040,/* Data direction (01:DATA IN) */
> CAM_DIR_OUT = 0x00000080,/* Data direction (10:DATA OUT) */
> CAM_DIR_NONE = 0x000000C0,/* Data direction (11:no data) */
> CAM_DIR_MASK = 0x000000C0,/* Data direction Mask */
>
> So to determine the data direction:
>
> if ((flags & CAM_DIR_MASK) == CAM_DIR_OUT)
> ...
I think CAM_DIR_MASK is a workaround for the original design flaw.
Comparing to UDI, only two defines versus five defines in CAM.
And one "&" operation versus two operations (&,==) in CAM.
Obviously, UDI is better at least here :-).
--
=============================
Tony Chung
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"Kenneth D. Merry" wrote:
<blockquote TYPE=CITE>Tony Chung wrote...
<br>>
<br>>
<br>> >
<br>> > 1 - Add a 'direction' field to the scsi command structure that
can be
<br>> > filled with the following values:
<br>> > DIR_INPUT, DIR_OUTPUT, DIR_NONE
and DIR_UNKNOWN=0
<br>> > Set this field to DIR_UNKNOWN=0
by default.
<br>> >
<br>>
<br>> >From Digital Unix /usr/include/io/cam.h:
<br>>
<br>> /* Defines for the CAM flags field in the CCB header. */
<br>>
<br>> #define CAM_DIR_RESV 0x00000000
/* Data direction (00: reserved) */
<br>> #define CAM_DIR_IN
0x00000040 /* Data direction (01: DATA IN) */
<br>> #define CAM_DIR_OUT 0x00000080
/* Data direction (10: DATA OUT) */
<br>> #define CAM_DIR_NONE 0x000000C0
/* Data direction (11: no data) */
<br>>
<br>> While UDI scsi spec has:
<br>> #define UDI_SCSI_DATA_IN (1U<<0)
<br>> #define UDI_SCSI_DATA_OUT (1U<<1)
<br>>
<br>> Basically, it can't be UNKNOWN because the Peripheral Driver must
specify the
<br>> buffer address and total transfer size. Any inconsistencies
should return error
<br>>
<br>> or let the host adaptor card simply return data overrun or data underrun.
<br>>
<br>>
<br>> I found CAM_DIR_NONE is potential hazard because
<br>> if some one specify CAM_DIR_NONE, another person
<br>> may mistakenly check for:
<br>> If (flags & CAM_DIR_OUT)
...../* condition true and do something wrong
<br>> */
<p>In FreeBSD/CAM, we added a mask:
<p> CAM_DIR_RESV
= 0x00000000,/* Data direction (00:reserved) */
<br> CAM_DIR_IN
= 0x00000040,/* Data direction (01:DATA IN) */
<br> CAM_DIR_OUT
= 0x00000080,/* Data direction (10:DATA OUT) */
<br> CAM_DIR_NONE
= 0x000000C0,/* Data direction (11:no data) */
<br> CAM_DIR_MASK
= 0x000000C0,/* Data direction Mask
*/
<p>So to determine the data direction:
<p>if ((flags & CAM_DIR_MASK) == CAM_DIR_OUT)
<br> ...</blockquote>
<pre>I think CAM_DIR_MASK is a workaround for the original design flaw.</pre>
<pre>Comparing to UDI, only two defines versus five defines in CAM.</pre>
<pre>And one "&" operation versus two operations (&,==) in CAM.</pre>
<pre>Obviously, UDI is better at least here :-).</pre>
<pre>--
=============================
Tony Chung</pre>
</html>
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