ACPI / sysfs: Add support to allow leading "\" missing in trace_method_name.

Since _SB.PCI0 can be used as relative path from root and can be easily
converted into internal trace_method_name format, we allow users to specify
trace_method_name using relative paths from root.
Note this is useful for grub2 for which users failed to pass "\" from the
grub configuration file.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 13 insertions, 15 deletions

diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
index 8979e4a8d066..40a42655227c 100644
--- a/drivers/acpi/sysfs.c
+++ b/drivers/acpi/sysfs.c
@@ -164,14 +164,18 @@ static const struct kernel_param_ops param_ops_debug_level = {
 module_param_cb(debug_layer, &param_ops_debug_layer, &acpi_dbg_layer, 0644);
 module_param_cb(debug_level, &param_ops_debug_level, &acpi_dbg_level, 0644);
 
-static char* trace_method_name;
-static bool trace_method_kmalloced;
+static char trace_method_name[1024];
 
 int param_set_trace_method_name(const char *val, const struct kernel_param *kp)
 {
         u32 saved_flags = 0;
+        bool is_abs_path = true;
 
-        if (strlen(val) > 1024) {
+        if (*val != '\\')
+                is_abs_path = false;
+
+        if ((is_abs_path && strlen(val) > 1023) ||
+            (!is_abs_path && strlen(val) > 1022)) {
                 pr_err("%s: string parameter too long\n", kp->name);
                 return -ENOSPC;
         }
@@ -187,19 +191,13 @@ int param_set_trace_method_name(const char *val, const struct kernel_param *kp)
                                acpi_gbl_trace_dbg_layer,
                                0);
 
-        if (trace_method_kmalloced)
-                kfree(trace_method_name);
-        trace_method_name = NULL;
-        trace_method_kmalloced = false;
-
         /* This is a hack.  We can't kmalloc in early boot. */
-        if (slab_is_available()) {
-                trace_method_name = kstrdup(val, GFP_KERNEL);
-                if (!trace_method_name)
-                        return -ENOMEM;
-                trace_method_kmalloced = true;
-        } else
-                trace_method_name = (char *)val;
+        if (is_abs_path)
+                strcpy(trace_method_name, val);
+        else {
+                trace_method_name[0] = '\\';
+                strcpy(trace_method_name+1, val);
+        }
 
         /* Restore the original tracer state */
         (void)acpi_debug_trace(trace_method_name,