Re: [dm-devel] [RFC][PATCH] Simplify dm_get_device restriction combining

[Mike Christie <mikenc us ibm com>]

Mike Christie wrote:

> Joe Thornber wrote:
>
> > On Tue, Jan 20, 2004 at 08:32:44PM +0100, Christophe Saout wrote:
> >
> > > To use blk_queue_stack_limits dm would have to associate a request queue
> > > with a table and swap it around too. I don't know if this is possible.
> > > dm doesn't use most of the fields in the request_queue struct.
> >
> >
> >
> > This would be the wrong thing.
>
>
> Right having the queue in the table would not work.
>
> In the constructor the target calls dm_get_device on it's devices and 
> combines the io restrictions for them. Then dm_table_add_target calls 
> combine_restrictions_low to combine the newly added targets restrictions.
>
> So, it looked like instead of combining the restrictions when you build 
> the table you could defer it until you bind. dm_table_set_restrictions 
> could just loop through its list of devices combining all the 
> restrictions then.

I meant, it looked like it would work becuase the targets seem to use 
their io restrictions for just combining restrictions, but at bind time 
the table has all the devices. What is the reason to perculate them up 
through the dm_dev, target and table during the building.

dm_table_set_restrictions could just do:

loop table->devices
	blk_queue_stack_limits(q, current device's queue);


Is there a target that uses the the limit variable for something else? I 
just did a grep through the source so I do not know for sure. Or will 
this be a problem with how the v1-ioctl binds and sets up tables - I am 
not too familir with it?

Mike