dquot: Detect partial write error to quota file in write_blk() and add printk_ratelimit for quota error messages

This patch changes quota_tree.c:write_blk() to detect error caused by partial
write to quota file and add a macro to limit control printed quota error
messages so we won't fill up dmesg with a corrupted quota file.

Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/quota/quota_tree.h b/fs/quota/quota_tree.h
index a1ab8db..ccc3e71 100644
--- a/fs/quota/quota_tree.h
+++ b/fs/quota/quota_tree.h
@@ -22,4 +22,10 @@
 
 #define QT_TREEOFF	1		/* Offset of tree in file in blocks */
 
+#define q_warn(fmt, args...) \
+do { \
+	if (printk_ratelimit()) \
+		printk(fmt, ## args); \
+} while(0)
+
 #endif /* _LINUX_QUOTAIO_TREE_H */