[PATCH] mtd: Add sysfs attribute for mtd OOB available size

[Xiaolei Li <xiaolei.li-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>]

Expose mtd OOB available size by sysfs file. Then users can get available
OOB size by accessing /sys/class/mtd/mtdX/oobavail.

Signed-off-by: Xiaolei Li <xiaolei.li-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>
---
 Documentation/ABI/testing/sysfs-class-mtd |  8 ++++++++
 drivers/mtd/mtdcore.c                     | 10 ++++++++++
 2 files changed, 18 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-mtd b/Documentation/ABI/testing/sysfs-class-mtd
index f34e5923..3bc7c0a 100644
--- a/Documentation/ABI/testing/sysfs-class-mtd
+++ b/Documentation/ABI/testing/sysfs-class-mtd
@@ -232,3 +232,11 @@ Description:
 		of the parent (another partition or a flash device) in bytes.
 		This attribute is absent on flash devices, so it can be used
 		to distinguish them from partitions.
+
+What:		/sys/class/mtd/mtdX/oobavail
+Date:		April 2018
+KernelVersion:	4.16
+Contact:	linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
+Description:
+		Number of bytes available for a client to place data into
+		the out of band area.
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 807d17d..99d9352 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -210,6 +210,15 @@ static ssize_t mtd_oobsize_show(struct device *dev,
 }
 static DEVICE_ATTR(oobsize, S_IRUGO, mtd_oobsize_show, NULL);
 
+static ssize_t mtd_oobavail_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct mtd_info *mtd = dev_get_drvdata(dev);
+
+	return snprintf(buf, PAGE_SIZE, "%lu\n", (unsigned long)mtd->oobavail);
+}
+static DEVICE_ATTR(oobavail, S_IRUGO, mtd_oobavail_show, NULL);
+
 static ssize_t mtd_numeraseregions_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
@@ -327,6 +336,7 @@ static ssize_t mtd_bbtblocks_show(struct device *dev,
 	&dev_attr_writesize.attr,
 	&dev_attr_subpagesize.attr,
 	&dev_attr_oobsize.attr,
+	&dev_attr_oobavail.attr,
 	&dev_attr_numeraseregions.attr,
 	&dev_attr_name.attr,
 	&dev_attr_ecc_strength.attr,
-- 
1.9.1