x86/intel_rdt: Export the minimum number of set mask bits in sysfs

The minimum number of bits set for a cache mask is checked by the kernel
when writing a mask, but there is no way for the user to retrieve this
information.

Add a new file 'min_cbm_bits' to the info directory and export the
information to user space.

[ tglx: Massaged changelog ]
Signed-off-by: Shaohua Li <shli@fb.com>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Link: http://lkml.kernel.org/r/e69b1ffa206d0353eea58101e1bf9b677d9732f7.1478207143.git.shli@fb.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

@@ -472,6 +472,16 @@ static int rdt_cbm_mask_show(struct kernfs_open_file *of,
 	return 0;
 }
 
+static int rdt_min_cbm_bits_show(struct kernfs_open_file *of,
+			     struct seq_file *seq, void *v)
+{
+	struct rdt_resource *r = of->kn->parent->priv;
+
+	seq_printf(seq, "%d\n", r->min_cbm_bits);
+
+	return 0;
+}
+
 /* rdtgroup information files for one cache resource. */
 static struct rftype res_info_files[] = {
 	{
@@ -486,6 +496,12 @@ static struct rftype res_info_files[] = {
 		.kf_ops		= &rdtgroup_kf_single_ops,
 		.seq_show	= rdt_cbm_mask_show,
 	},
+	{
+		.name		= "min_cbm_bits",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdt_min_cbm_bits_show,
+	},
 };
 
 static int rdtgroup_create_info_dir(struct kernfs_node *parent_kn)