Re: [PATCH 2.5.17] Making SCSI not copy the request structure

[Doug Ledford <dledford@redhat.com>]

On Thu, May 23, 2002 at 03:01:37AM +0100, Alan Cox wrote:
> One thing I see consistently as a problem in the block layers in 2.4 is
> that there is no way to say "thanks for the request you just threw at me
> but Im busy right now" and to flag "busy/idle".
> 
> The network layer has a clean way to say "Im busy dont feed me",
> "Im no longer busy, feed me" and also "thanks but I've just discovered I
> am in fact busy have this request back anbd feed it me later"

No, that does in fact exist.  At least in the new scsi eh code you are 
allowed to return a non-0 value from your low level driver's 
queuecommand() routine.  On a non-0 return, the mid layer throws the 
command onto the mlqueue and waits to send it until the mid layer 
processes a completion event from you (or there might also be a timeout, 
I'm not sure, but I would hope there is also a timeout since otherwise 
returning non-0 with no outstanding commands on a device because your 
driver is busy with something else could cause a queue to hang).  Anyway, 
it's there even if I never did personally use it since my driver used the 
old eh code ;-)

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606