Re: [PATCH / RFC] scsi_error handler update. (1/4)

[James Bottomley <James.Bottomley@steeleye.com>]

On Mon, 2003-02-17 at 12:20, Luben Tuikov wrote:
> There is no ``locking hierarchy'' -- i.e. a lock *only* locks its list
> manipulation. So, you don't have to have a string of locks to change
> a scsi_command, for example.

If I want to loop over all outstanding commands on a device (say because
the FC has just got a LIP removal), how do I do it?  Your design implies
I have to loop over all portals, targets and luns.  To do this loop, I'd
have to stabilise all the lists by acquiring the three locks that
protect them, wouldn't I?

> When was the last time a SPI HBA set channel/bus to anything different
> than 0?

Channel is a special abstraction for the dual channel chips.  It's
really an extension of host number for drivers that need a channel
decode.  The mid-layer only uses it for the host reset function, since
resetting the host 

> My Adaptec AIC-7899P dual channel, presents two hosts, not two channels.
> And this is the right behaviour.

The adaptec driver certainly uses the multiple channel feature, but only
if the AHC_TWIN flag is set in the host.

> > 3. I don't see where the mid-layer has a use for the data.  By and
> 
> Well, how can I contend *that* statement?...  This basically means
> that the whole thing I proposed is cr*p.

This is the key issue.  Complexity should only be introduced in a design
when it serves a justifiable purpose.  How do the 4 layers you propose
simplify the design/improve the throughput or in any other way add
benefit over the two layers (host and device) that we already have?

Because the standards say so isn't enough.  The Mid-layer's job is to
make efficient use of devices which follow the standards as simply and
elegantly as possible, not mirror the SCSI architecture model.

James