[PATCH v4 29/31] fs/resctrl: Add interface for per-resource debug info files

[Tony Luck <tony.luck@intel.com>]

There are some status registers on each of the telemetry aggregators.
Users may need to view these to understand unexpected event counter
values.

Add the file system support for a "status" file in each mon_capable
resource directory in the "info" directory. This will only be present if
the file system is mounted with the "-o debug" option. It will only have
content for resources that provide a rdt_resource::info_debug() routine.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 include/linux/resctrl.h |  1 +
 fs/resctrl/rdtgroup.c   | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 3ae50b947a99..675cfbe3e6c6 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -299,6 +299,7 @@ struct rdt_resource {
 	struct list_head	evt_list;
 	unsigned int		mbm_cfg_mask;
 	bool			cdp_capable;
+	void			(*info_debug)(struct seq_file *s);
 };
 
 /*
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 195e41eb73fb..5948e279b44c 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1022,6 +1022,17 @@ static int rdt_shareable_bits_show(struct kernfs_open_file *of,
 	return 0;
 }
 
+static int rdtgroup_info_debug_show(struct kernfs_open_file *of,
+				struct seq_file *s, void *v)
+{
+	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
+
+	if (r->info_debug)
+		r->info_debug(s);
+
+	return 0;
+}
+
 /*
  * rdt_bit_usage_show - Display current usage of resources
  *
@@ -1983,6 +1994,13 @@ static struct rftype res_common_files[] = {
 		.seq_show	= rdtgroup_closid_show,
 		.fflags		= RFTYPE_CTRL_BASE | RFTYPE_DEBUG,
 	},
+	{
+		.name		= "status",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdtgroup_info_debug_show,
+		.fflags		= RFTYPE_MON_INFO | RFTYPE_DEBUG,
+	},
 };
 
 static int rdtgroup_add_files(struct kernfs_node *kn, unsigned long fflags)
-- 
2.48.1