x86/intel_rdt: Add cpus_list rdtgroup file

The resource control filesystem provides only a bitmask based cpus file for
assigning CPUs to a resource group. That's cumbersome with large cpumasks
and non-intuitive when modifying the file from the command line.

Range based cpu lists are commonly used along with bitmask based cpu files
in various subsystems throughout the kernel.

Add 'cpus_list' file which is CPU range based.

  # cd /sys/fs/resctrl/
  # echo 1-10 > krava/cpus_list
  # cat krava/cpus_list
  1-10
  # cat krava/cpus
  0007fe
  # cat cpus
  fffff9
  # cat cpus_list
  0,3-23

[ tglx: Massaged changelog and replaced "bitmask lists" by "CPU ranges" ]
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Shaohua Li <shli@fb.com>
Link: http://lkml.kernel.org/r/20170410145232.GF25354@kravaSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

Documentation/x86/intel_rdt_ui.txt

@@ -59,6 +59,9 @@ There are three files associated with each group:
 	given to the default (root) group. You cannot remove CPUs
 	from the default group.
 
+"cpus_list": One or more CPU ranges of logical CPUs assigned to this
+	     group. Same rules apply like for the "cpus" file.
+
 "schemata": A list of all the resources available to this group.
 	Each resource has its own line and format - see below for
 	details.

arch/x86/include/asm/intel_rdt.h

@@ -37,6 +37,9 @@ struct rdtgroup {
 /* rdtgroup.flags */
 #define	RDT_DELETED		1
 
+/* rftype.flags */
+#define RFTYPE_FLAGS_CPUS_LIST	1
+
 /* List of all resource groups */
 extern struct list_head rdt_all_groups;
 
@@ -49,6 +52,7 @@ int __init rdtgroup_init(void);
  * @name:	File name
  * @mode:	Access mode
  * @kf_ops:	File operations
+ * @flags:	File specific RFTYPE_FLAGS_* flags
  * @seq_show:	Show content of the file
  * @write:	Write to the file
  */
@@ -56,6 +60,7 @@ struct rftype {
 	char			*name;
 	umode_t			mode;
 	struct kernfs_ops	*kf_ops;
+	unsigned long		flags;
 
 	int (*seq_show)(struct kernfs_open_file *of,
 			struct seq_file *sf, void *v);

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

@@ -174,6 +174,13 @@ static struct kernfs_ops rdtgroup_kf_single_ops = {
 	.seq_show		= rdtgroup_seqfile_show,
 };
 
+static bool is_cpu_list(struct kernfs_open_file *of)
+{
+	struct rftype *rft = of->kn->priv;
+
+	return rft->flags & RFTYPE_FLAGS_CPUS_LIST;
+}
+
 static int rdtgroup_cpus_show(struct kernfs_open_file *of,
 			      struct seq_file *s, void *v)
 {
@@ -182,10 +189,12 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
 
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
 
-	if (rdtgrp)
-		seq_printf(s, "%*pb\n", cpumask_pr_args(&rdtgrp->cpu_mask));
-	else
+	if (rdtgrp) {
+		seq_printf(s, is_cpu_list(of) ? "%*pbl\n" : "%*pb\n",
+			   cpumask_pr_args(&rdtgrp->cpu_mask));
+	} else {
 		ret = -ENOENT;
+	}
 	rdtgroup_kn_unlock(of->kn);
 
 	return ret;
@@ -252,7 +261,11 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 		goto unlock;
 	}
 
+	if (is_cpu_list(of))
+		ret = cpulist_parse(buf, newmask);
+	else
 		ret = cpumask_parse(buf, newmask);
+
 	if (ret)
 		goto unlock;
 
@@ -472,6 +485,14 @@ static struct rftype rdtgroup_base_files[] = {
 		.write		= rdtgroup_cpus_write,
 		.seq_show	= rdtgroup_cpus_show,
 	},
+	{
+		.name		= "cpus_list",
+		.mode		= 0644,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.write		= rdtgroup_cpus_write,
+		.seq_show	= rdtgroup_cpus_show,
+		.flags		= RFTYPE_FLAGS_CPUS_LIST,
+	},
 	{
 		.name		= "tasks",
 		.mode		= 0644,