fs: Add a function to set the filesystem type

When sandbox is used with hostfs we won't have a block device, but still
must set up the filesystem type before any filesystem operation, such as
loading a file. Add a function to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/fs/fs.c b/fs/fs.c
index b812597..6de1a3eb6 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -36,6 +36,11 @@
 static struct disk_partition fs_partition;
 static int fs_type = FS_TYPE_ANY;
 
+void fs_set_type(int type)
+{
+	fs_type = type;
+}
+
 static inline int fs_probe_unsupported(struct blk_desc *fs_dev_desc,
 				      struct disk_partition *fs_partition)
 {
diff --git a/include/fs.h b/include/fs.h
index e2beba3..b43f16a 100644
--- a/include/fs.h
+++ b/include/fs.h
@@ -57,6 +57,17 @@
  */
 int fs_set_blk_dev(const char *ifname, const char *dev_part_str, int fstype);
 
+/**
+ * fs_set_type() - Tell fs layer which filesystem type is used
+ *
+ * This is needed when reading from a non-block device such as sandbox. It does
+ * a similar job to fs_set_blk_dev() but just sets the filesystem type instead
+ * of detecting it and loading it on the block device
+ *
+ * @type: Filesystem type to use (FS_TYPE...)
+ */
+void fs_set_type(int type);
+
 /*
  * fs_set_blk_dev_with_part - Set current block device + partition
  *