All files below /sys/fs/resctrl are considered user ABI.

This leaves no place for architectures to provide additional
interfaces.

Add resctrl_debugfs_mon_info_arch_mkdir() which creates a directory in
the debugfs file system for a monitoring resource. Naming follows the
layout of the main resctrl hierarchy:

	/sys/kernel/debug/resctrl/info/{resource}_MON/{arch}

The {arch} last level directory name matches the output of
the user level "uname -m" command.

Architecture code may use this directory for debug information,
or for minor tuning of features. It must not be used for basic
feature enabling as debugfs may not be configured/mounted on
production systems.

Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 include/linux/resctrl.h |  9 +++++++++
 fs/resctrl/rdtgroup.c   | 29 +++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 1f42bc761377..8a010c29c8b4 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -569,6 +569,15 @@ void resctrl_arch_reset_all_ctrls(struct rdt_resource *r);
 extern unsigned int resctrl_rmid_realloc_threshold;
 extern unsigned int resctrl_rmid_realloc_limit;
 
+/**
+ * resctrl_debugfs_mon_info_arch_mkdir() - Create a debugfs info directory.
+ *					   Removed by resctrl_exit().
+ * @r:	Resource (must be mon_capable).
+ *
+ * Return: dentry pointer on success, or NULL on error.
+ */
+struct dentry *resctrl_debugfs_mon_info_arch_mkdir(struct rdt_resource *r);
+
 int resctrl_init(void);
 void resctrl_exit(void);
 
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 886de0e01e8a..8f0bcb139a74 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -24,6 +24,7 @@
 #include <linux/sched/task.h>
 #include <linux/slab.h>
 #include <linux/user_namespace.h>
+#include <linux/utsname.h>
 
 #include <uapi/linux/magic.h>
 
@@ -75,6 +76,8 @@ static void rdtgroup_destroy_root(void);
 
 struct dentry *debugfs_resctrl;
 
+static struct dentry *debugfs_resctrl_info;
+
 /*
  * Memory bandwidth monitoring event to use for the default CTRL_MON group
  * and each new CTRL_MON group created by the user.  Only relevant when
@@ -4355,6 +4358,31 @@ int resctrl_init(void)
 	return ret;
 }
 
+/*
+ * Create /sys/kernel/debug/resctrl/info/{r->name}_MON/{arch} directory
+ * by request for architecture to use for debugging or minor tuning.
+ * Basic functionality of features must not be controlled by files
+ * added to this directory as debugfs may not be configured/mounted
+ * on production systems.
+ */
+struct dentry *resctrl_debugfs_mon_info_arch_mkdir(struct rdt_resource *r)
+{
+	struct dentry *moninfodir;
+	char name[32];
+
+	if (!r->mon_capable)
+		return NULL;
+
+	if (!debugfs_resctrl_info)
+		debugfs_resctrl_info = debugfs_create_dir("info", debugfs_resctrl);
+
+	sprintf(name, "%s_MON", r->name);
+
+	moninfodir = debugfs_create_dir(name, debugfs_resctrl_info);
+
+	return debugfs_create_dir(utsname()->machine, moninfodir);
+}
+
 static bool resctrl_online_domains_exist(void)
 {
 	struct rdt_resource *r;
@@ -4406,6 +4434,7 @@ void resctrl_exit(void)
 
 	debugfs_remove_recursive(debugfs_resctrl);
 	debugfs_resctrl = NULL;
+	debugfs_resctrl_info = NULL;
 	unregister_filesystem(&rdt_fs_type);
 
 	/*
-- 
2.50.1

Hi Tony,

On 8/29/25 12:33 PM, Tony Luck wrote:
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 1f42bc761377..8a010c29c8b4 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -569,6 +569,15 @@ void resctrl_arch_reset_all_ctrls(struct rdt_resource *r);
>  extern unsigned int resctrl_rmid_realloc_threshold;
>  extern unsigned int resctrl_rmid_realloc_limit;
>  
> +/**
> + * resctrl_debugfs_mon_info_arch_mkdir() - Create a debugfs info directory.
> + *					   Removed by resctrl_exit().
> + * @r:	Resource (must be mon_capable).
> + *
> + * Return: dentry pointer on success, or NULL on error.

NULL is returned if resource is not monitoring capable, otherwise
it returns debugfs_create_dir() which is ERR_PTR(-ERROR) on failure.

Reinette