mtd: part: Add sysfs variable for offset of partition

This patch makes a sysfs variable called 'offset' on each partition
which contains the offset in bytes from the beginning of the master
device that the partition starts.

Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

2 files changed, 39 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-mtd b/Documentation/ABI/testing/sysfs-class-mtd
index 76ee192f80a0..3b5c3bca9186 100644
--- a/Documentation/ABI/testing/sysfs-class-mtd
+++ b/Documentation/ABI/testing/sysfs-class-mtd
@@ -222,3 +222,13 @@ Description:
                 The number of blocks that are marked as reserved, if any, in
                 this partition. These are typically used to store the in-flash
                 bad block table (BBT).
+
+What:           /sys/class/mtd/mtdX/offset
+Date:           March 2015
+KernelVersion:  4.1
+Contact:        linux-mtd@lists.infradead.org
+Description:
+                For a partition, the offset of that partition from the start
+                of the master device in bytes. This attribute is absent on
+                main devices, so it can be used to distinguish between
+                partitions and devices that aren't partitions.
diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
index a19ec5a4e409..be8034086701 100644
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -554,6 +554,30 @@ out_register:
         return slave;
 }
 
+static ssize_t mtd_partition_offset_show(struct device *dev,
+                struct device_attribute *attr, char *buf)
+{
+        struct mtd_info *mtd = dev_get_drvdata(dev);
+        struct mtd_part *part = PART(mtd);
+        return snprintf(buf, PAGE_SIZE, "%lld\n", part->offset);
+}
+
+static DEVICE_ATTR(offset, S_IRUGO, mtd_partition_offset_show, NULL);
+
+static const struct attribute *mtd_partition_attrs[] = {
+        &dev_attr_offset.attr,
+        NULL
+};
+
+static int mtd_add_partition_attrs(struct mtd_part *new)
+{
+        int ret = sysfs_create_files(&new->mtd.dev.kobj, mtd_partition_attrs);
+        if (ret)
+                printk(KERN_WARNING
+                       "mtd: failed to create partition attrs, err=%d\n", ret);
+        return ret;
+}
+
 int mtd_add_partition(struct mtd_info *master, const char *name,
                       long long offset, long long length)
 {
@@ -603,6 +627,8 @@ int mtd_add_partition(struct mtd_info *master, const char *name,
 
         add_mtd_device(&new->mtd);
 
+        mtd_add_partition_attrs(new);
+
         return ret;
 err_inv:
         mutex_unlock(&mtd_partitions_mutex);
@@ -620,6 +646,8 @@ int mtd_del_partition(struct mtd_info *master, int partno)
         list_for_each_entry_safe(slave, next, &mtd_partitions, list)
                 if ((slave->master == master) &&
                     (slave->mtd.index == partno)) {
+                        sysfs_remove_files(&slave->mtd.dev.kobj,
+                                           mtd_partition_attrs);
                         ret = del_mtd_device(&slave->mtd);
                         if (ret < 0)
                                 break;
@@ -663,6 +691,7 @@ int add_mtd_partitions(struct mtd_info *master,
                 mutex_unlock(&mtd_partitions_mutex);
 
                 add_mtd_device(&slave->mtd);
+                mtd_add_partition_attrs(slave);
 
                 cur_offset = slave->offset + slave->mtd.size;
         }