[PATCH 2/2] dmi-id: add dmi/id/oem group for exporting oem strings to sysfs

[Allen Hung <allen_hung@dell.com>]

The oem strings in DMI system identification information of the BIOS have
been parsed and stored as dmi devices in dmi_scan.c but they are not
exported to userspace via sysfs.

The patch intends to export oem strings to sysfs device /sys/class/dmi/id.
As the number of oem strings are dynamic, a group "oem" is added to the
device and the strings will be added to the group as string1, string2, ...,
and stringN.

Signed-off-by: Allen Hung <allen_hung@dell.com>
---
 drivers/firmware/dmi-id.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)

diff --git a/drivers/firmware/dmi-id.c b/drivers/firmware/dmi-id.c
index 44c0139..f284a07 100644
--- a/drivers/firmware/dmi-id.c
+++ b/drivers/firmware/dmi-id.c
@@ -58,6 +58,107 @@ DEFINE_DMI_ATTR_WITH_SHOW(chassis_version,	0444, DMI_CHASSIS_VERSION);
 DEFINE_DMI_ATTR_WITH_SHOW(chassis_serial,	0400, DMI_CHASSIS_SERIAL);
 DEFINE_DMI_ATTR_WITH_SHOW(chassis_asset_tag,	0444, DMI_CHASSIS_ASSET_TAG);
 
+static struct attribute *dmi_oem_attrs[] = {
+	NULL,
+};
+
+static const char oem_group[] = "oem";
+
+static struct attribute_group dmi_oem_attr_group = {
+	.attrs = dmi_oem_attrs,
+	.name  = oem_group,
+};
+
+static LIST_HEAD(dmi_oem_attrs_list);
+
+struct dmi_oem_attribute {
+	struct device_attribute dev_attr;
+	const char *oem_string;
+	char buf[32];
+	bool is_added:1;
+	struct list_head list;
+};
+
+#define to_dmi_oem_attr(_dev_attr) \
+	container_of(_dev_attr, struct dmi_oem_attribute, dev_attr)
+
+static ssize_t sys_dmi_oem_show(struct device *dev,
+				  struct device_attribute *attr,
+				  char *page)
+{
+	struct dmi_oem_attribute *oa = to_dmi_oem_attr(attr);
+	ssize_t len;
+
+	strlcpy(page, oa->oem_string, PAGE_SIZE-1);
+	len = strlen(page);
+	page[len++] = '\n';
+	page[len] = 0;
+	return len;
+}
+
+static int __init dmi_id_init_oem_attr_group(void)
+{
+	int i, ret;
+	const struct dmi_device *dev;
+	struct dmi_oem_attribute *oa, *tmp;
+	struct device_attribute dev_attr_tmpl =
+		__ATTR(, 0444, sys_dmi_oem_show, NULL);
+
+	ret = sysfs_create_group(&dmi_dev->kobj, &dmi_oem_attr_group);
+	if (ret)
+		return ret;
+
+	/* All devices with type=DMI_DEV_TYPE_OEM_STRING will be found in
+	 * the reverse order of what they were parsed in dmi_scan.c. However,
+	 * we do want to expose the OEM strings to sysfs in the same order as
+	 * what they were originally parsed. A linked list with 2-pass method
+	 * is used here to reverse the reserved order.
+	 *
+	 * Pass 1: find out all "OEM string" devices and add each "oem string"
+	 * to a linked list.
+	 */
+	dev = dmi_find_device(DMI_DEV_TYPE_OEM_STRING, NULL, NULL);
+	while (dev)  {
+		oa = kzalloc(sizeof(*oa), GFP_KERNEL);
+		if (!oa) {
+			ret = -ENOMEM;
+			goto failed;
+		}
+		oa->dev_attr = dev_attr_tmpl;
+		oa->oem_string = dev->name;
+		list_add(&oa->list, &dmi_oem_attrs_list);
+		dev = dmi_find_device(DMI_DEV_TYPE_OEM_STRING, NULL, dev);
+	}
+
+	/* Pass 2: traverse the list and add each string as a file to "oem"
+	 * group
+	 */
+	i = 0;
+	list_for_each_entry(oa, &dmi_oem_attrs_list, list) {
+		snprintf(oa->buf, sizeof(oa->buf), "string%d", ++i);
+		oa->dev_attr.attr.name = oa->buf;
+		ret = sysfs_add_file_to_group(
+			&dmi_dev->kobj, &oa->dev_attr.attr, oem_group);
+		if (ret)
+			goto failed;
+		oa->is_added = 1;
+	}
+
+	return 0;
+
+failed:
+	list_for_each_entry_safe(oa, tmp, &dmi_oem_attrs_list, list) {
+		if (oa->is_added)
+			sysfs_remove_file_from_group(
+				&dmi_dev->kobj,	&oa->dev_attr.attr, oem_group);
+		list_del(&oa->list);
+		kfree(oa);
+	}
+	sysfs_remove_group(&dmi_dev->kobj, &dmi_oem_attr_group);
+
+	return ret;
+}
+
 static void ascii_filter(char *d, const char *s)
 {
 	/* Filter out characters we don't want to see in the modalias string */
@@ -231,8 +332,15 @@ static int __init dmi_id_init(void)
 	if (ret)
 		goto fail_put_dmi_dev;
 
+	ret = dmi_id_init_oem_attr_group();
+	if (ret)
+		goto fail_dev_unregister;
+
 	return 0;
 
+fail_dev_unregister:
+	device_unregister(dmi_dev);
+
 fail_put_dmi_dev:
 	put_device(dmi_dev);
 
-- 
2.7.4