Rename library_offset to library_fd_offset

 replace lseek() and use pread() instead
 add test for library_fd_offset > file_size case

Bug: 17762003
Change-Id: I4555f0be635124efe849c1f226985bcba72ffcbd
diff --git a/libc/include/android/dlext.h b/libc/include/android/dlext.h
index f81ec70..f27e4e5 100644
--- a/libc/include/android/dlext.h
+++ b/libc/include/android/dlext.h
@@ -54,11 +54,11 @@
    */
   ANDROID_DLEXT_USE_LIBRARY_FD        = 0x10,
 
-  /* When opening library using library_fd read it starting with library_offset
+  /* If opening a library using library_fd read it starting at library_fd_offset.
    * This flag is only valid when ANDROID_DLEXT_USE_LIBRARY_FD is set.
    */
 
-  ANDROID_DLEXT_USE_LIBRARY_OFFSET    = 0x20,
+  ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET    = 0x20,
 
   /* Mask of valid bits */
   ANDROID_DLEXT_VALID_FLAG_BITS       = ANDROID_DLEXT_RESERVED_ADDRESS |
@@ -66,7 +66,7 @@
                                         ANDROID_DLEXT_WRITE_RELRO |
                                         ANDROID_DLEXT_USE_RELRO |
                                         ANDROID_DLEXT_USE_LIBRARY_FD |
-                                        ANDROID_DLEXT_USE_LIBRARY_OFFSET,
+                                        ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET,
 };
 
 typedef struct {
@@ -75,7 +75,7 @@
   size_t  reserved_size;
   int     relro_fd;
   int     library_fd;
-  off64_t library_offset;
+  off64_t library_fd_offset;
 } android_dlextinfo;
 
 extern void* android_dlopen_ext(const char* filename, int flag, const android_dlextinfo* extinfo);