fastboot: add support for auto-resparsing large files

Add support to fastboot for automatically using libsparse to break large
files, whether they are in sparse or normal format, into multiple sparse
files that can each fit into the target's memory.  Allows flashing
images that are larger than the size of the available memory on the
target.

By default, any file over 512MB will be sparsed into 512MB chunks.  The
limit can be modified with the -m argument, or sparsing can be forced
with -S or avoided with -N.  If -m is not specified, the target can
override the default by implementing getvar:max-download-size

Change-Id: I6c59381c3d24475c4f2587ea877200b96971cbd7
diff --git a/fastboot/util_windows.c b/fastboot/util_windows.c
index c3d545c..9e029fd 100644
--- a/fastboot/util_windows.c
+++ b/fastboot/util_windows.c
@@ -36,6 +36,29 @@
 
 #include <windows.h>
 
+int64_t file_size(const char *fn)
+{
+    HANDLE    file;
+    char     *data;
+    DWORD     sz;
+
+    file = CreateFile( fn,
+                       GENERIC_READ,
+                       FILE_SHARE_READ,
+                       NULL,
+                       OPEN_EXISTING,
+                       0,
+                       NULL );
+
+    if (file == INVALID_HANDLE_VALUE)
+        return -1;
+
+    sz = GetFileSize( file, NULL );
+    CloseHandle( file );
+
+    return sz;
+}
+
 void get_my_path(char exe[PATH_MAX])
 {
 	char*  r;
@@ -52,7 +75,7 @@
 {
     HANDLE    file;
     char     *data;
-    DWORD     file_size;
+    DWORD     sz;
 
     file = CreateFile( fn,
                        GENERIC_READ,
@@ -65,29 +88,29 @@
     if (file == INVALID_HANDLE_VALUE)
         return NULL;
 
-    file_size = GetFileSize( file, NULL );
+    sz = GetFileSize( file, NULL );
     data      = NULL;
 
-    if (file_size > 0) {
-        data = (char*) malloc( file_size );
+    if (sz > 0) {
+        data = (char*) malloc( sz );
         if (data == NULL) {
-            fprintf(stderr, "load_file: could not allocate %ld bytes\n", file_size );
-            file_size = 0;
+            fprintf(stderr, "load_file: could not allocate %ld bytes\n", sz );
+            sz = 0;
         } else {
             DWORD  out_bytes;
 
-            if ( !ReadFile( file, data, file_size, &out_bytes, NULL ) ||
-                 out_bytes != file_size )
+            if ( !ReadFile( file, data, sz, &out_bytes, NULL ) ||
+                 out_bytes != sz )
             {
-                fprintf(stderr, "load_file: could not read %ld bytes from '%s'\n", file_size, fn);
+                fprintf(stderr, "load_file: could not read %ld bytes from '%s'\n", sz, fn);
                 free(data);
                 data      = NULL;
-                file_size = 0;
+                sz = 0;
             }
         }
     }
     CloseHandle( file );
 
-    *_sz = (unsigned) file_size;
+    *_sz = (unsigned) sz;
     return  data;
 }