James -
On Wed, Jul 31, 2002 at 11:04:13AM -0500, James Bottomley wrote:
> patmans@xxxxxxxxxx said:
> > Having Scsi_Device on its own list could also help in hot-replacement
> > of single pathed devices (Scsi_Host can be removed without having to
> > remove a Scsi_Device off of its host_queue).
>
> Isn't this going to cause serious problems for the driverfs stuff?
> Effectively you're changing the parent pointer under the device which alters
> the layout of the device tree.
Yes, for any multi-path implementation, driverfs needs changes so that a
child can have multiple parents, or something along those lines.
For the next version of the patch, I'm planning on merging with the current
identifier code - the value put into the driverfs "name", and then I plan
on looking into driverfs changes.
Perhaps driverfs could seperate device registration (or creation) from link
(or path) registration.
> > If you make changes in the host/device list(s) please consider that I
> > need to have the Scsi_Devices on their own list separate from the
> > Scsi_host list.
>
> Could you post some of the details of this (separated from the multi-path
> patch if possible)? Thanks,
>
> James
There is a document here:
http://www-124.ibm.com/storageio/multipath/scsi-multipath/docs/index.html
It describes the current host_queue list (I think you had similiar
slides at OLS), and the new list introduced by the multi-path patch,
mainly to show the path structures, not the Scsi_Device list.
Generally, if we want one Scsi_Device per actual LUN, and a LUN is connected
to multiple adapters, the Scsi_Device can't easily be linked off of
Scsi_Host - there is no longer one Scsi_Host for a given Scsi_Device.
So, I added a list of Scsi_Devices; on each Scsi_Device there is a list
of paths, where each path includes a pointer back to Scsi_Host.
On removal of a single Scsi_Host (if there was such code), all paths
pointing to the host must first be removed, and Scsi_Device can remain
(even with no left paths).
If I linked off of Scsi_Host, there would have to be a separate list
structure so that a Scsi_Device could be on multiple Scsi_Host lists.
This could still be done even with a separate Scsi_Device list, but is
only usefull if we need a fast way to lookup all Scsi_Devices on a host.
-- Patrick Mansfield
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