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

[Peter Jones <pjones@redhat.com>]

On 04/07/2009 04:59 PM, 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

(Chandra covered this pretty well, so I'll leave it be.)

>      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.

This seems backwards to me.  It's not trying to work around a problem
in the initrd tools; it's trying to avoid creating one by making this
subsystem unlike others.

The point of having modaliases is to allow the kernel to announce that it's
got a hardware device and notify the userland that appropriate modules should
be loaded.  That's exactly what we've done here.  What we're trying to avoid
in the initrd tools is having to have a special handler for this subsystem;
instead, we'd much rather use the generic mechanism that already exists for
this purpose.

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

Can you please explain what the high risks you're thinking of are?  I'm not
clear on what undesirable behavior you expect to occur.

The reward is that scsi targets behave exactly like most other types of
hardware and kernel modules in this regard, without having to write special
probing for this subsystem in the userland and special handling for loading
these modules.  That's a pretty big win for maintainability.

-- 
        Peter