Re: [PATCH v3 3/7] drivers/base/node: Add support to write node_states[] via sysfs

["ying.huang@intel.com" <ying.huang@intel.com>]

On Sat, 2022-04-23 at 01:25 +0530, Jagdish Gediya wrote:
> Current /sys/devices/system/node/* interface doesn't support
> to write node_states[], however write support is needed in case
> users want to set them manually e.g. when user want to override
> default N_DEMOTION_TARGETS found by the kernel.
> 
> Rename existing _NODE_ATTR to _NODE_ATTR_RO and introduce new
> _NODE_ATTR_RW which can be used for node_states[] which can
> be written from sysfs.
> 
> It may be necessary to validate written values and take action
> based on them in a state specific way so a callback 'write' is
> introduced in 'struct node_attr'.
> 
> A new function demotion_targets_write() is added to validate
> the input nodes for N_DEMOTION_TARGETS which should be subset
> of N_MEMORY and to build new demotion list based on new nodes.
> 
> Signed-off-by: Jagdish Gediya <jvgediya@linux.ibm.com>

How about discussing the ABI design firstly?  I started a discussion in
the following thread.  I think we can start with the requirements.

https://lore.kernel.org/lkml/200e95cf36c1642512d99431014db8943fed715d.camel@intel.com/

Best Regards,
Huang, Ying

> ---
>  drivers/base/node.c | 62 +++++++++++++++++++++++++++++++++++----------
>  1 file changed, 49 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 6eef22e6413e..e03eedbc421b 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -20,6 +20,7 @@
>  #include <linux/pm_runtime.h>
>  #include <linux/swap.h>
>  #include <linux/slab.h>
> +#include <linux/migrate.h>
>  
> 
> 
> 
>  static struct bus_type node_subsys = {
>  	.name = "node",
> @@ -1013,6 +1014,7 @@ void unregister_one_node(int nid)
>  struct node_attr {
>  	struct device_attribute attr;
>  	enum node_states state;
> +	int (*write)(nodemask_t nodes);
>  };
>  
> 
> 
> 
>  static ssize_t show_node_state(struct device *dev,
> @@ -1024,23 +1026,57 @@ static ssize_t show_node_state(struct device *dev,
>  			  nodemask_pr_args(&node_states[na->state]));
>  }
>  
> 
> 
> 
> -#define _NODE_ATTR(name, state) \
> -	{ __ATTR(name, 0444, show_node_state, NULL), state }
> +static ssize_t store_node_state(struct device *s,
> +				struct device_attribute *attr,
> +				const char *buf, size_t count)
> +{
> +	nodemask_t nodes;
> +	struct node_attr *na = container_of(attr, struct node_attr, attr);
> +
> +	if (nodelist_parse(buf, nodes))
> +		return -EINVAL;
> +
> +	if (na->write) {
> +		if (na->write(nodes))
> +			return -EINVAL;
> +	} else {
> +		node_states[na->state] = nodes;
> +	}
> +
> +	return count;
> +}
> +
> +static int demotion_targets_write(nodemask_t nodes)
> +{
> +	if (nodes_subset(nodes, node_states[N_MEMORY])) {
> +		node_states[N_DEMOTION_TARGETS] = nodes;
> +		set_migration_target_nodes();
> +		return 0;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +#define _NODE_ATTR_RO(name, state) \
> +	{ __ATTR(name, 0444, show_node_state, NULL), state, NULL }
> +
> +#define _NODE_ATTR_RW(name, state, write_fn) \
> +	{ __ATTR(name, 0644, show_node_state, store_node_state), state, write_fn }
>  
> 
> 
> 
>  static struct node_attr node_state_attr[] = {
> -	[N_POSSIBLE] = _NODE_ATTR(possible, N_POSSIBLE),
> -	[N_ONLINE] = _NODE_ATTR(online, N_ONLINE),
> -	[N_NORMAL_MEMORY] = _NODE_ATTR(has_normal_memory, N_NORMAL_MEMORY),
> +	[N_POSSIBLE] = _NODE_ATTR_RO(possible, N_POSSIBLE),
> +	[N_ONLINE] = _NODE_ATTR_RO(online, N_ONLINE),
> +	[N_NORMAL_MEMORY] = _NODE_ATTR_RO(has_normal_memory, N_NORMAL_MEMORY),
>  #ifdef CONFIG_HIGHMEM
> -	[N_HIGH_MEMORY] = _NODE_ATTR(has_high_memory, N_HIGH_MEMORY),
> +	[N_HIGH_MEMORY] = _NODE_ATTR_RO(has_high_memory, N_HIGH_MEMORY),
>  #endif
> -	[N_MEMORY] = _NODE_ATTR(has_memory, N_MEMORY),
> -	[N_CPU] = _NODE_ATTR(has_cpu, N_CPU),
> -	[N_GENERIC_INITIATOR] = _NODE_ATTR(has_generic_initiator,
> -					   N_GENERIC_INITIATOR),
> -	[N_DEMOTION_TARGETS] = _NODE_ATTR(demotion_targets,
> -					  N_DEMOTION_TARGETS),
> -
> +	[N_MEMORY] = _NODE_ATTR_RO(has_memory, N_MEMORY),
> +	[N_CPU] = _NODE_ATTR_RO(has_cpu, N_CPU),
> +	[N_GENERIC_INITIATOR] = _NODE_ATTR_RO(has_generic_initiator,
> +					      N_GENERIC_INITIATOR),
> +	[N_DEMOTION_TARGETS] = _NODE_ATTR_RW(demotion_targets,
> +					     N_DEMOTION_TARGETS,
> +					     demotion_targets_write),
>  };
>  
> 
> 
> 
>  static struct attribute *node_state_attrs[] = {