Re: [PATCH 1/3] scsi_dh: Add modalias support for SCSI targets

Chandra Seetharaman
2009-04-07T23:41:40Z

Thanks for the response James.
On Tue, 2009-04-07 at 20:59 +0000, James Bottomley wrote:
> On Fri, 2009-04-03 at 15:43 -0700, Chandra Seetharaman wrote:
> > Hi James,
> >
> > Do you still have any concerns (after Peter's response) ?
>
> Yes, the basic concerns still remain:
>
> 1. You're forcing autoload now even if the user isn't running
> dm ... this is going to cause problems with non-dm based path
> handlers

As I mentioned in an earlier email, the purpose of moving the device
handler to SCSI layer from dm layer was to make sure that the device
in-differences are taken care of.

For example, the lsi rdac storage is active/passive and we do want the
SCSI layer to handle appropriately so that the I/O is not tried
repeatedly in the passive path. With the device handler in SCSI layer we
were able to handle it properly, thereby reducing the boot time nicely.

So, for all practical purposes these device handlers serve a purpose by
themselves, even without dm-multipath ever needing to use it.

What dm-multipath does by way of calling scsi_dh_activate can also be
done by the interface Hannes added to the sysfs.

> 2. autoloading in this fashion is essentially trying to work around
> a problem in the initrd tools. The kernel isn't the right place
> to implement the fix.

I defer this question to Peter :)

>
> The risks of this approach seem very high, and the rewards pretty small.
>
> James
>
>
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