ext4: implement exists() for ext4fs

This hooks into the generic "file exists" support added in an earlier
patch, and provides an implementation for the ext4 filesystem.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

fs/ext4/ext4fs.c

@@ -174,6 +174,14 @@ int ext4fs_ls(const char *dirname)
 	return 0;
 }
 
+int ext4fs_exists(const char *filename)
+{
+	int file_len;
+
+	file_len = ext4fs_open(filename);
+	return file_len >= 0;
+}
+
 int ext4fs_read(char *buf, unsigned len)
 {
 	if (ext4fs_root == NULL || ext4fs_file == NULL)

fs/fs.c

@@ -102,7 +102,7 @@ static struct fstype_info fstypes[] = {
 		.probe = ext4fs_probe,
 		.close = ext4fs_close,
 		.ls = ext4fs_ls,
-		.exists = fs_exists_unsupported,
+		.exists = ext4fs_exists,
 		.read = ext4_read_file,
 		.write = fs_write_unsupported,
 	},

include/ext4fs.h

@@ -134,6 +134,7 @@ int ext4fs_read(char *buf, unsigned len);
 int ext4fs_mount(unsigned part_length);
 void ext4fs_close(void);
 int ext4fs_ls(const char *dirname);
+int ext4fs_exists(const char *filename);
 void ext4fs_free_node(struct ext2fs_node *node, struct ext2fs_node *currroot);
 int ext4fs_devread(lbaint_t sector, int byte_offset, int byte_len, char *buf);
 void ext4fs_set_blk_dev(block_dev_desc_t *rbdd, disk_partition_t *info);