Re: dm: retain stacked max_sectors when setting queue_limits

[Ming Lei <ming.lei@redhat.com>]

On Wed, May 22, 2024 at 12:48:59PM -0400, Mike Snitzer wrote:
> On Wed, May 22, 2024 at 04:24:58PM +0200, Christoph Hellwig wrote:
> > On Tue, May 21, 2024 at 10:51:17PM -0400, Mike Snitzer wrote:
> > > Otherwise, blk_validate_limits() will throw-away the max_sectors that
> > > was stacked from underlying device(s). In doing so it can set a
> > > max_sectors limit that violates underlying device limits.
> > 
> > Hmm, yes it sort of is "throwing the limit away", but it really
> > recalculates it from max_hw_sectors, max_dev_sectors and user_max_sectors.
> 
> Yes, but it needs to do that recalculation at each level of a stacked
> device.  And then we need to combine them via blk_stack_limits() -- as
> is done with the various limits stacking loops in
> drivers/md/dm-table.c:dm_calculate_queue_limits

This way looks one stacking specific requirement, just wondering why not
put the logic into blk_validate_limits() by passing 'stacking' parameter?
Then raid can benefit from it oo.

thanks,
Ming