Re: [PATCH] scsi: storvsc: set max_segment_size as UINT_MAX explicitly

[Christoph Hellwig <hch@lst.de>]

On Tue, Jun 17, 2025 at 03:25:21PM +0800, Ming Lei wrote:
> > @@ -473,7 +473,9 @@ struct Scsi_Host *scsi_host_alloc(const struct scsi_host_template *sht, int priv
> >  	else
> >  		shost->max_sectors = SCSI_DEFAULT_MAX_SECTORS;
> >  
> > -	if (sht->max_segment_size)
> > +	if (sht->virt_boundary_mask)
> > +		shost->virt_boundary_mask = sht->virt_boundary_mask;
> > +	else if (sht->max_segment_size)
> >  		shost->max_segment_size = sht->max_segment_size;
> >  	else
> >  		shost->max_segment_size = BLK_MAX_SEGMENT_SIZE;
> 
> This way works, but I prefer to set it explicitly in driver, instead of
> making block layer more fragile to deal with def ->max_segment_size
> if ->virt_boundary_mask is defined

The block layer already enforces this as it is a requirement.  It is
just the SCSI wrapper that broke it.  Without this proper fix iser
is still broken, and srp might or might not.

> - for low level driver, if ->virt_boundary_mask is defined, ->max_segment_size
> should be UINT_MAX obviously since it implies single `virt segment`.
> Setting UINT_MAX in driver has document benefit too.

No, it doesn't.  It means you need to cargo cult copy and paste code
instead of solving the problem in the proper place.

> - for logical block device(md, dm, ...), both ->virt_boundary_mask and
> ->max_segment_size may be set, and it is fine since logical block device
> driver needn't to deal with sg

Stacked devices should not inherit the hardware limits at all because
we split below them, but that's a separate story.  Either way this is
not relevant here as we don't have stacking drivers that use the
SCSI layer.