[PATCH] dmi_check_system can generate Warnings when no DMI table is present

[Erwan Velu <erwanaliasr1@gmail.com>]

When running the Linux Kernel, on some systems that doesn't have any DMI 
table (like a Xen domU), some dmi_* calls can generates Warnings like :

>/ WARNING: at /usr/src/linux-2.6.29.1/drivers/firmware/dmi_scan.c:425/
>/ dmi_matches+0x7e/0x80()/
>/ dmi check: not initialized yet/

Some users reported this error :
http://lists.xensource.com/archives/html/xen-users/2009-04/msg00128.html
https://qa.mandriva.com/show_bug.cgi?id=54775

When the kernel is compiled with CONFIG_DMI, dmi_check_system(), 
dmi_first_match(), dmi_name_in_vendors(), dmi_find_device(), 
dmi_get_date(), dmi_match() calls doesn't check the status of the 
dmi_available variable.

When this functions are called and if no valid dmi table has been found, 
this pretty simple patch just return the default values returned when 
CONFIG_DMI isn't set.

This patch applies to the lastest git tree.
I'm CCing the x86 maintainers as I can't find any maintainer of 
drivers/firmware/dmi.

Signed-off-by: Erwan Velu <erwanaliasr1@gmail.com>


diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index 938100f..ea8b433 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -457,6 +457,9 @@ int dmi_check_system(const struct dmi_system_id *list)
     int count = 0;
     const struct dmi_system_id *d;
 
+    if (!dmi_available)
+        return 0;
+
     for (d = list; d->ident; d++)
         if (dmi_matches(d)) {
             count++;
@@ -484,6 +487,9 @@ const struct dmi_system_id *dmi_first_match(const 
struct dmi_system_id *list)
 {
     const struct dmi_system_id *d;
 
+    if (!dmi_available)
+        return NULL;
+
     for (d = list; d->ident; d++)
         if (dmi_matches(d))
             return d;
@@ -501,6 +507,9 @@ EXPORT_SYMBOL(dmi_first_match);
  */
 const char *dmi_get_system_info(int field)
 {
+    if (!dmi_available)
+        return NULL;
+
     return dmi_ident[field];
 }
 EXPORT_SYMBOL(dmi_get_system_info);
@@ -512,6 +521,10 @@ EXPORT_SYMBOL(dmi_get_system_info);
 int dmi_name_in_serial(const char *str)
 {
     int f = DMI_PRODUCT_SERIAL;
+
+    if (!dmi_available)
+        return 0;
+
     if (dmi_ident[f] && strstr(dmi_ident[f], str))
         return 1;
     return 0;
@@ -527,6 +540,10 @@ int dmi_name_in_vendors(const char *str)
                 DMI_PRODUCT_NAME, DMI_PRODUCT_VERSION, DMI_BOARD_VENDOR,
                 DMI_BOARD_NAME, DMI_BOARD_VERSION, DMI_NONE };
     int i;
+
+    if (!dmi_available)
+        return 0;
+
     for (i = 0; fields[i] != DMI_NONE; i++) {
         int f = fields[i];
         if (dmi_ident[f] && strstr(dmi_ident[f], str))
@@ -554,6 +571,9 @@ const struct dmi_device * dmi_find_device(int type, 
const char *name,
     const struct list_head *head = from ? &from->list : &dmi_devices;
     struct list_head *d;
 
+    if (!dmi_available)
+        return NULL;
+
     for(d = head->next; d != &dmi_devices; d = d->next) {
         const struct dmi_device *dev =
             list_entry(d, struct dmi_device, list);
@@ -592,6 +612,16 @@ bool dmi_get_date(int field, int *yearp, int 
*monthp, int *dayp)
     const char *s, *y;
     char *e;
 
+    if (!dmi_available) {
+            if (yearp)
+                    *yearp = 0;
+            if (monthp)
+                    *monthp = 0;
+            if (dayp)
+                    *dayp = 0;
+            return false;
+    }
+
     s = dmi_get_system_info(field);
     exists = s;
     if (!exists)
@@ -676,6 +706,9 @@ bool dmi_match(enum dmi_field f, const char *str)
 {
     const char *info = dmi_get_system_info(f);
 
+    if (!dmi_available)
+        return false;
+
     if (info == NULL || str == NULL)
         return info == str;