Re: [ndctl PATCH] ndctl: fail NUMA filtering when unsupported

["Verma, Vishal L" <vishal.l.verma@intel.com>]

On Fri, 2018-03-09 at 16:34 -0700, Ross Zwisler wrote:
> For systems that don't support NUMA, numactl gives a loud and fatal
> error:
> 
>   # numactl -N 0 ls
>   numactl: This system does not support NUMA policy
> 
> Follow this model in ndctl for NUMA based filtering:
> 
>   # ./ndctl/ndctl list --numa-node=0
>     Error: This system does not support NUMA
> 
> This is done instead of just quietly filtering out all dimms, regions
> and
> namespaces because the NUMA node they were trying to match didn't
> exist in
> the system.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  util/filter.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/util/filter.c b/util/filter.c
> index 291d7ed..fdc46a3 100644
> --- a/util/filter.c
> +++ b/util/filter.c
> @@ -14,7 +14,10 @@
>  #include <string.h>
>  #include <stdlib.h>
>  #include <limits.h>
> +#include <unistd.h>
> +#include <sys/stat.h>
>  #include <util/util.h>
> +#include <sys/types.h>
>  #include <ndctl/ndctl.h>
>  #include <util/filter.h>
>  #include <ndctl/libndctl.h>
> @@ -328,6 +331,13 @@ int util_filter_walk(struct ndctl_ctx *ctx,
> struct util_filter_ctx *fctx,
>  	}
>  
>  	if (param->numa_node && strcmp(param->numa_node, "all") !=
> 0) {
> +		struct stat st;
> +
> +		if (stat("/sys/devices/system/node", &st)) {
> +			error("This system does not support
> NUMA\n");
> +			return -EINVAL;
> +		}

Is it ok to just directly read sysfs here? Alternatively we could use
the get_mempolicy syscall (like libnuma does) but that requires linking
with -lnuma..

https://github.com/numactl/numactl/blob/master/libnuma.c#L800

> +
>  		numa_node = strtol(param->numa_node, &end, 0);
>  		if (end == param->numa_node || end[0]) {
>  			error("invalid numa_node: '%s'\n", param-
> >numa_node);
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