[PATCH 1/5] x86/intel_rdt: Add framework for better RDT UI diagnostics

[Luck, Tony]

From: Tony Luck <tony.luck@xxxxxxxxx>

Commands are given to the resctrl file system by making/removing
directories, or by writing to files.  When something goes wrong
the user is generally left wondering why they got:

	bash: echo: write error: Invalid argument

Add a new file "last_cmd_status" to the "info" directory that
will give the user some better clues on what went wrong.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
 arch/x86/kernel/cpu/intel_rdt.h          |  6 ++++++
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 33 ++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel_rdt.h b/arch/x86/kernel/cpu/intel_rdt.h
index ebaddaeef023..afba509ac164 100644
--- a/arch/x86/kernel/cpu/intel_rdt.h
+++ b/arch/x86/kernel/cpu/intel_rdt.h
@@ -2,6 +2,7 @@
 #define _ASM_X86_INTEL_RDT_H
 
 #include <linux/sched.h>
+#include <linux/seq_buf.h>
 #include <linux/kernfs.h>
 #include <linux/jump_label.h>
 
@@ -30,6 +31,8 @@
 
 DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
 
+extern struct seq_buf last_cmd_status;
+
 /**
  * struct mon_evt - Entry in the event list of a resource
  * @evtid:		event id
@@ -126,12 +129,15 @@ struct rdtgroup {
 #define RFTYPE_BASE			BIT(1)
 #define RF_CTRLSHIFT			4
 #define RF_MONSHIFT			5
+#define RF_TOPSHIFT			6
 #define RFTYPE_CTRL			BIT(RF_CTRLSHIFT)
 #define RFTYPE_MON			BIT(RF_MONSHIFT)
+#define RFTYPE_TOP			BIT(RF_TOPSHIFT)
 #define RFTYPE_RES_CACHE		BIT(8)
 #define RFTYPE_RES_MB			BIT(9)
 #define RF_CTRL_INFO			(RFTYPE_INFO | RFTYPE_CTRL)
 #define RF_MON_INFO			(RFTYPE_INFO | RFTYPE_MON)
+#define RF_TOP_INFO			(RFTYPE_INFO | RFTYPE_TOP)
 #define RF_CTRL_BASE			(RFTYPE_BASE | RFTYPE_CTRL)
 
 /* List of all resource groups */
diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index a869d4a073c5..6a2cd89fa9de 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -51,6 +51,9 @@ static struct kernfs_node *kn_mongrp;
 /* Kernel fs node for "mon_data" directory under root */
 static struct kernfs_node *kn_mondata;
 
+struct seq_buf last_cmd_status;
+static char last_cmd_status_buf[512];
+
 /*
  * Trivial allocator for CLOSIDs. Since h/w only supports a small number,
  * we can keep a bitmap of free CLOSIDs in a single integer.
@@ -569,6 +572,21 @@ static int rdtgroup_tasks_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+static int rdt_last_cmd_status_show(struct kernfs_open_file *of,
+				    struct seq_file *seq, void *v)
+{
+	int len;
+
+	mutex_lock(&rdtgroup_mutex);
+	len = seq_buf_used(&last_cmd_status);
+	if (len)
+		seq_printf(seq, "%.*s", len, last_cmd_status_buf);
+	else
+		seq_puts(seq, "ok\n");
+	mutex_unlock(&rdtgroup_mutex);
+	return 0;
+}
+
 static int rdt_num_closids_show(struct kernfs_open_file *of,
 				struct seq_file *seq, void *v)
 {
@@ -686,6 +704,13 @@ static ssize_t max_threshold_occ_write(struct kernfs_open_file *of,
 /* rdtgroup information files for one cache resource. */
 static struct rftype res_common_files[] = {
 	{
+		.name		= "last_cmd_status",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdt_last_cmd_status_show,
+		.fflags		= RF_TOP_INFO,
+	},
+	{
 		.name		= "num_closids",
 		.mode		= 0444,
 		.kf_ops		= &rdtgroup_kf_single_ops,
@@ -855,6 +880,10 @@ static int rdtgroup_create_info_dir(struct kernfs_node *parent_kn)
 		return PTR_ERR(kn_info);
 	kernfs_get(kn_info);
 
+	ret = rdtgroup_add_files(kn_info, RF_TOP_INFO);
+	if (ret)
+		goto out_destroy;
+
 	for_each_alloc_enabled_rdt_resource(r) {
 		fflags =  r->fflags | RF_CTRL_INFO;
 		ret = rdtgroup_mkdir_info_resdir(r, r->name, fflags);
@@ -1156,6 +1185,7 @@ static struct dentry *rdt_mount(struct file_system_type *fs_type,
 out_cdp:
 	cdp_disable();
 out:
+	seq_buf_clear(&last_cmd_status);
 	mutex_unlock(&rdtgroup_mutex);
 
 	return dentry;
@@ -1902,6 +1932,9 @@ int __init rdtgroup_init(void)
 {
 	int ret = 0;
 
+	seq_buf_init(&last_cmd_status, last_cmd_status_buf,
+		     sizeof(last_cmd_status_buf));
+
 	ret = rdtgroup_setup_root();
 	if (ret)
 		return ret;
-- 
2.11.0