scsi: core: Add 'serial' sysfs attribute for SCSI/SATA

Add a 'serial' sysfs attribute for SCSI and SATA devices. This attribute
exposes the Unit Serial Number, which is derived from the Device
Identification Vital Product Data (VPD) page 0x80.

Whitespace is stripped from the retrieved serial number to handle the
different alignment (right-aligned for SCSI, potentially left-aligned for
SATA). As noted in SAT-5 10.5.3, "Although SPC-5 defines the PRODUCT SERIAL
NUMBER field as right-aligned, ACS-5 does not require its SERIAL NUMBER
field to be right-aligned. Therefore, right-alignment of the PRODUCT SERIAL
NUMBER field for the translation is not assured."

This attribute is used by tools such as lsblk to display the serial number
of block devices.

[mkp: length adjustment]

Signed-off-by: Igor Pylypiv <ipylypiv@google.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://patch.msgid.link/20260209212151.342151-1-ipylypiv@google.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_lib.c

@@ -13,6 +13,7 @@
 #include <linux/bitops.h>
 #include <linux/blkdev.h>
 #include <linux/completion.h>
+#include <linux/ctype.h>
 #include <linux/kernel.h>
 #include <linux/export.h>
 #include <linux/init.h>
@@ -3460,6 +3461,52 @@ int scsi_vpd_lun_id(struct scsi_device *sdev, char *id, size_t id_len)
 }
 EXPORT_SYMBOL(scsi_vpd_lun_id);
 
+/**
+ * scsi_vpd_lun_serial - return a unique device serial number
+ * @sdev: SCSI device
+ * @sn:   buffer for the serial number
+ * @sn_size: size of the buffer
+ *
+ * Copies the device serial number into @sn based on the information in
+ * the VPD page 0x80 of the device. The string will be null terminated
+ * and have leading and trailing whitespace stripped.
+ *
+ * Returns the length of the serial number or error on failure.
+ */
+int scsi_vpd_lun_serial(struct scsi_device *sdev, char *sn, size_t sn_size)
+{
+	const struct scsi_vpd *vpd_pg80;
+	const unsigned char *d;
+	int len;
+
+	guard(rcu)();
+	vpd_pg80 = rcu_dereference(sdev->vpd_pg80);
+	if (!vpd_pg80)
+		return -ENXIO;
+
+	len = vpd_pg80->len - 4;
+	d = vpd_pg80->data + 4;
+
+	/* Skip leading spaces */
+	while (len > 0 && isspace(*d)) {
+		len--;
+		d++;
+	}
+
+	/* Skip trailing spaces */
+	while (len > 0 && isspace(d[len - 1]))
+		len--;
+
+	if (sn_size < len + 1)
+		return -EINVAL;
+
+	memcpy(sn, d, len);
+	sn[len] = '\0';
+
+	return len;
+}
+EXPORT_SYMBOL(scsi_vpd_lun_serial);
+
 /**
  * scsi_vpd_tpg_id - return a target port group identifier
  * @sdev: SCSI device

drivers/scsi/scsi_sysfs.c

@@ -1051,6 +1051,21 @@ sdev_show_wwid(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR(wwid, S_IRUGO, sdev_show_wwid, NULL);
 
+static ssize_t
+sdev_show_serial(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(dev);
+	ssize_t ret;
+
+	ret = scsi_vpd_lun_serial(sdev, buf, PAGE_SIZE - 1);
+	if (ret < 0)
+		return ret;
+
+	buf[ret] = '\n';
+	return ret + 1;
+}
+static DEVICE_ATTR(serial, S_IRUGO, sdev_show_serial, NULL);
+
 #define BLIST_FLAG_NAME(name)					\
 	[const_ilog2((__force __u64)BLIST_##name)] = #name
 static const char *const sdev_bflags_name[] = {
@@ -1295,6 +1310,7 @@ static struct attribute *scsi_sdev_attrs[] = {
 	&dev_attr_device_busy.attr,
 	&dev_attr_vendor.attr,
 	&dev_attr_model.attr,
+	&dev_attr_serial.attr,
 	&dev_attr_rev.attr,
 	&dev_attr_rescan.attr,
 	&dev_attr_delete.attr,

include/scsi/scsi_device.h

@@ -571,6 +571,7 @@ void scsi_put_internal_cmd(struct scsi_cmnd *scmd);
 extern void sdev_disable_disk_events(struct scsi_device *sdev);
 extern void sdev_enable_disk_events(struct scsi_device *sdev);
 extern int scsi_vpd_lun_id(struct scsi_device *, char *, size_t);
+extern int scsi_vpd_lun_serial(struct scsi_device *, char *, size_t);
 extern int scsi_vpd_tpg_id(struct scsi_device *, int *);
 
 #ifdef CONFIG_PM