From 0a04ed86cfaa36d93d55016d0b3dc3f06352a2fe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C5=81ukasz=20Majewski?= <l.majewski@samsung.com>
Date: Thu, 3 Sep 2015 14:21:39 +0200
Subject: FIX: fat: Provide correct return code from disk_{read|write} to upper
 layers

It is very common that FAT code is using following pattern:
if (disk_{read|write}() < 0)
        return -1;

Up till now the above code was dead, since disk_{read|write) could only
return value >= 0.
As a result some errors from medium layer (i.e. eMMC/SD) were not caught.

The above behavior was caused by block_{read|write|erase} declared at
struct block_dev_desc (@part.h). It returns unsigned long, where 0
indicates error and > 0 indicates that medium operation was correct.

This patch as error regards 0 returned from block_{read|write|erase}
when nr_blocks is grater than zero. Read/Write operation with nr_blocks=0
should return 0 and hence is not considered as an error.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>

Test HW: Odroid XU3 - Exynos 5433

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 06dcbb7..f939bc5 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -46,11 +46,18 @@ static disk_partition_t cur_part_info;
 
 static int disk_read(__u32 block, __u32 nr_blocks, void *buf)
 {
+	ulong ret;
+
 	if (!cur_dev || !cur_dev->block_read)
 		return -1;
 
-	return cur_dev->block_read(cur_dev->dev,
-			cur_part_info.start + block, nr_blocks, buf);
+	ret = cur_dev->block_read(cur_dev->dev,
+				  cur_part_info.start + block, nr_blocks, buf);
+
+	if (nr_blocks && ret == 0)
+		return -1;
+
+	return ret;
 }
 
 int fat_set_blk_dev(block_dev_desc_t *dev_desc, disk_partition_t *info)
diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
index 98b88ad..adb6940 100644
--- a/fs/fat/fat_write.c
+++ b/fs/fat/fat_write.c
@@ -30,6 +30,8 @@ static void uppercase(char *str, int len)
 static int total_sector;
 static int disk_write(__u32 block, __u32 nr_blocks, void *buf)
 {
+	ulong ret;
+
 	if (!cur_dev || !cur_dev->block_write)
 		return -1;
 
@@ -39,8 +41,13 @@ static int disk_write(__u32 block, __u32 nr_blocks, void *buf)
 		return -1;
 	}
 
-	return cur_dev->block_write(cur_dev->dev,
-			cur_part_info.start + block, nr_blocks,	buf);
+	ret = cur_dev->block_write(cur_dev->dev,
+				   cur_part_info.start + block,
+				   nr_blocks, buf);
+	if (nr_blocks && ret == 0)
+		return -1;
+
+	return ret;
 }
 
 /*
-- 
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