Re: [PATCH v10 25/31] dax/bus: Reject resize on DC dax devices and enforce 0-size creation

[Anisa Su <anisa.su887@gmail.com>]

On Fri, May 29, 2026 at 10:16:10AM -0700, Dave Jiang wrote:
> 
> 
> On 5/23/26 2:43 AM, Anisa Su wrote:
> > A DC dax device's size is determined by the extents that back it, not by
> > the user.  DCD extents are all-or-nothing, so partial shrink is just as
> > illegal as growing.  Enforce that on the size and creation paths:
> > 
> >   * size_store: any non-zero resize on a DC region returns -EOPNOTSUPP.
> >     The sole exception is size=0, which daxctl destroy-device writes to
> >     return every claimed extent to the region's available pool before
> >     the device's name is written to the region's 'delete' attribute.
> >   * __devm_create_dev_dax: a DC dax device must be created at size 0.
> >     Non-zero data->size on a DC region returns -EINVAL with a clear
> >     message.
> > 
> > The resize machinery (dev_dax_shrink, adjust_ok, dev_dax_resize_static,
> > dev_dax_resize) learns to walk the right parent — dax_region->res for
> > static regions, the dax_resource->res for DC regions claimed via
> > uuid_store — so shrink-to-0 correctly releases each extent's child
> > resource rather than the region's.
> > 
> > Based on an original patch by Navneet Singh.
> > 
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> > Signed-off-by: Anisa Su <anisa.su@samsung.com>
> 
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> 
> Just a nit below.
> 
> 
> > 
> > ---
> > Changes:
> > [anisa: split out from the original "Surface dc_extents" commit;
> >  DC-aware resize policy only.]
> > ---
> >  drivers/dax/bus.c | 46 +++++++++++++++++++++++++++++++++++-----------
> >  1 file changed, 35 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> > index 1d6f82920be6..c030eb103ad0 100644
> > --- a/drivers/dax/bus.c
> > +++ b/drivers/dax/bus.c
> > @@ -1136,7 +1136,8 @@ static int dev_dax_shrink(struct dev_dax *dev_dax, resource_size_t size)
> >  	int i;
> >  
> >  	for (i = dev_dax->nr_range - 1; i >= 0; i--) {
> > -		struct range *range = &dev_dax->ranges[i].range;
> > +		struct dev_dax_range *dev_range = &dev_dax->ranges[i];
> > +		struct range *range = &dev_range->range;
> >  		struct dax_mapping *mapping = dev_dax->ranges[i].mapping;
> >  		struct resource *adjust = NULL, *res;
> >  		resource_size_t shrink;
> > @@ -1152,6 +1153,10 @@ static int dev_dax_shrink(struct dev_dax *dev_dax, resource_size_t size)
> >  			continue;
> >  		}
> >  
> > +		/*
> > +		 * Partial shrink: forbidden on DC regions, so dev_range
> > +		 * here must belong to a static device.
> > +		 */
> >  		for_each_dax_region_resource(dax_region, res)
> >  			if (strcmp(res->name, dev_name(dev)) == 0
> >  					&& res->start == range->start) {
> > @@ -1195,19 +1200,21 @@ static bool adjust_ok(struct dev_dax *dev_dax, struct resource *res)
> >  }
> >  
> >  /**
> > - * dev_dax_resize_static - Expand the device into the unused portion of the
> > - * region. This may involve adjusting the end of an existing resource, or
> > - * allocating a new resource.
> > + * __dev_dax_resize - Expand the device into the unused portion of the region.
> > + * This may involve adjusting the end of an existing resource, or allocating a
> > + * new resource.
> >   *
> >   * @parent: parent resource to allocate this range in
> >   * @dev_dax: DAX device to be expanded
> >   * @to_alloc: amount of space to alloc; must be <= space available in @parent
> > + * @dax_resource: if dc; the parent resource
> >   *
> >   * Return the amount of space allocated or -ERRNO on failure
> >   */
> > -static ssize_t dev_dax_resize_static(struct resource *parent,
> > -				     struct dev_dax *dev_dax,
> > -				     resource_size_t to_alloc)
> > +static ssize_t __dev_dax_resize(struct resource *parent,
> > +				struct dev_dax *dev_dax,
> > +				resource_size_t to_alloc,
> > +				struct dax_resource *dax_resource)
> >  {
> >  	struct resource *res, *first;
> >  	int rc;
> > @@ -1215,7 +1222,8 @@ static ssize_t dev_dax_resize_static(struct resource *parent,
> >  	first = parent->child;
> >  	if (!first) {
> >  		rc = alloc_dev_dax_range(parent, dev_dax,
> > -					   parent->start, to_alloc, NULL);
> > +					   parent->start, to_alloc,
> > +					   dax_resource);
> >  		if (rc)
> >  			return rc;
> >  		return to_alloc;
> > @@ -1229,7 +1237,8 @@ static ssize_t dev_dax_resize_static(struct resource *parent,
> >  		if (res == first && res->start > parent->start) {
> >  			alloc = min(res->start - parent->start, to_alloc);
> >  			rc = alloc_dev_dax_range(parent, dev_dax,
> > -						 parent->start, alloc, NULL);
> > +						 parent->start, alloc,
> > +						 dax_resource);
> >  			if (rc)
> >  				return rc;
> >  			return alloc;
> > @@ -1253,7 +1262,8 @@ static ssize_t dev_dax_resize_static(struct resource *parent,
> >  				return rc;
> >  			return alloc;
> >  		}
> > -		rc = alloc_dev_dax_range(parent, dev_dax, res->end + 1, alloc, NULL);
> > +		rc = alloc_dev_dax_range(parent, dev_dax, res->end + 1, alloc,
> > +					 dax_resource);
> >  		if (rc)
> >  			return rc;
> >  		return alloc;
> > @@ -1264,6 +1274,13 @@ static ssize_t dev_dax_resize_static(struct resource *parent,
> >  	return 0;
> >  }
> >  
> > +static ssize_t dev_dax_resize_static(struct dax_region *dax_region,
> > +				     struct dev_dax *dev_dax,
> > +				     resource_size_t to_alloc)
> > +{
> > +	return __dev_dax_resize(&dax_region->res, dev_dax, to_alloc, NULL);
> > +}
> > +
> >  static ssize_t dev_dax_resize(struct dax_region *dax_region,
> >  		struct dev_dax *dev_dax, resource_size_t size)
> >  {
> > @@ -1277,6 +1294,8 @@ static ssize_t dev_dax_resize(struct dax_region *dax_region,
> >  		return -EBUSY;
> >  	if (size == dev_size)
> >  		return 0;
> > +	if (size != 0 && is_dynamic(dax_region))
> > +		return -EOPNOTSUPP;
> >  	if (size > dev_size && size - dev_size > avail)
> >  		return -ENOSPC;
> >  	if (size < dev_size)
> > @@ -1288,7 +1307,7 @@ static ssize_t dev_dax_resize(struct dax_region *dax_region,
> >  		return -ENXIO;
> >  
> >  retry:
> > -	alloc = dev_dax_resize_static(&dax_region->res, dev_dax, to_alloc);
> > +	alloc = dev_dax_resize_static(dax_region, dev_dax, to_alloc);
> >  	if (alloc <= 0)
> >  		return alloc;
> >  	to_alloc -= alloc;
> > @@ -1674,6 +1693,11 @@ static struct dev_dax *__devm_create_dev_dax(struct dev_dax_data *data)
> >  	struct device *dev;
> >  	int rc;
> >  
> > +	if (is_dynamic(dax_region) && data->size) {
> > +		dev_err(parent, "DC DAX region devices must be created initially with 0 size");
> 
> Needs \n
> 
Fixed!

Thanks,
Anisa
> > +		return ERR_PTR(-EINVAL);
> > +	}
> > +
> >  	dev_dax = kzalloc_obj(*dev_dax);
> >  	if (!dev_dax)
> >  		return ERR_PTR(-ENOMEM);
>