[PATCH v2 4/6] x86/intel_rdt: Add diagnostics when writing the cpus file

[Luck, Tony]

From: Tony Luck <tony.l...@intel.com>

Can't add a cpu to a monitor group unless it belongs to parent
group. Can't delete cpus from the default group.

Signed-off-by: Tony Luck <tony.l...@intel.com>
---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c 
b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index df6373680a59..1674f7871b06 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -264,8 +264,10 @@ static int cpus_mon_write(struct rdtgroup *rdtgrp, 
cpumask_var_t newmask,
 
        /* Check whether cpus belong to parent ctrl group */
        cpumask_andnot(tmpmask, newmask, &prgrp->cpu_mask);
-       if (cpumask_weight(tmpmask))
+       if (cpumask_weight(tmpmask)) {
+               rdt_last_cmd_puts("can only add CPUs to mongroup that belong to 
parent\n");
                return -EINVAL;
+       }
 
        /* Check whether cpus are dropped from this group */
        cpumask_andnot(tmpmask, &rdtgrp->cpu_mask, newmask);
@@ -317,8 +319,10 @@ static int cpus_ctrl_write(struct rdtgroup *rdtgrp, 
cpumask_var_t newmask,
        cpumask_andnot(tmpmask, &rdtgrp->cpu_mask, newmask);
        if (cpumask_weight(tmpmask)) {
                /* Can't drop from default group */
-               if (rdtgrp == &rdtgroup_default)
+               if (rdtgrp == &rdtgroup_default) {
+                       rdt_last_cmd_puts("Can't drop CPUs from default 
group\n");
                        return -EINVAL;
+               }
 
                /* Give any dropped cpus to rdtgroup_default */
                cpumask_or(&rdtgroup_default.cpu_mask,
@@ -383,8 +387,10 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file 
*of,
        }
 
        rdtgrp = rdtgroup_kn_lock_live(of->kn);
+       rdt_last_cmd_clear();
        if (!rdtgrp) {
                ret = -ENOENT;
+               rdt_last_cmd_puts("directory was removed\n");
                goto unlock;
        }
 
@@ -393,13 +399,16 @@ static ssize_t rdtgroup_cpus_write(struct 
kernfs_open_file *of,
        else
                ret = cpumask_parse(buf, newmask);
 
-       if (ret)
+       if (ret) {
+               rdt_last_cmd_puts("bad cpu list/mask\n");
                goto unlock;
+       }
 
        /* check that user didn't specify any offline cpus */
        cpumask_andnot(tmpmask, newmask, cpu_online_mask);
        if (cpumask_weight(tmpmask)) {
                ret = -EINVAL;
+               rdt_last_cmd_puts("can only assign online cpus\n");
                goto unlock;
        }
 
-- 
2.11.0