There is also an older depreciated ioctl style of generics interface
which could also use the same logic as it has the same problem. Building
the table into sg is probably not the best place for it, but the table could
go in the mid-layer as a function and then both bits of code could call into
it to figure out the data direction.
It would be helpful if the people who knew the most about the
limitations of the various tables scattered through the various low-level
drivers would pick one that is believed to be the most accurate and
comprehensive. The thing I still don't know about is how to handle vendor
specific commands - in particular something like cdparanoia is probably
going to use these quite frequently, and we really haven't solved everything
by adding the table to resolve ambiguities.
I had kind of hoped that all drivers could tolerate (with the possible
loss of performance) having the flag set to UNKNOWN. In this way we would
be assured of a fallback position that would at least function without
screwing up the system. In conjunction with a table, we could set the
direction correctly for non-vendor specific commands, and force it to
UNKNOWN for vendor specific commands. This would eliminate the possibility
of an ill-behaved application screwing up the system.
-Eric
----- Original Message -----
From: Matthew Dharm <[EMAIL PROTECTED]>
To: Alan Cox <[EMAIL PROTECTED]>
Cc: Eric Youngdale <[EMAIL PROTECTED]>; The Linux SCSI list
<[EMAIL PROTECTED]>
Sent: Wednesday, April 19, 2000 3:28 PM
Subject: Re: sc_data_direction -- will we require it?
> On Wed, 19 Apr 2000, Alan Cox wrote:
>
> > > Yes, this is a known limitation of the generics interface.
Perhaps Doug
> > > has further comments. I am wondering whether we need some sort of
table
> > > (not unlike what you already have) to set the data direction in the
generics
> > > interface if it isn't specified by the user. The major bugaboo is
going to
> > > be vendor specific commands, as tables are not going to be of much
> > > assistance here.
> >
> > For the general commands IBM have a pretty complete table in the
> > serveraid driver. We maybe ought to actually put the table into sg
> > instead of duplicated around all sorts of drivers ?
>
> This sounds like an excellent idea. Is there any chance of getting this
> in before 2.4?
>
> Matt Dharm
>
> --
> Matthew Dharm Home: [EMAIL PROTECTED]
> Engineer, Qualcomm, Inc. Work: [EMAIL PROTECTED]
>
> I'm seen in many forms. Now open your mouth. It's caffeine time.
> -- Cola Man to Greg
> User Friendly, 10/28/1998
>
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