ART: Unlink old file in OS::CreateEmptyFile

Update the documentation to make clear that a new file is expected
to be returned. A potentially existing file will not be reused
(and cleared).

Bug: 22047255
Change-Id: I0eb8601c7696d6f7b81547abcc06ff605826dc26

2 files changed, 6 insertions, 1 deletions

diff --git a/runtime/os.h b/runtime/os.h
index 6248d5fc14..befe2e808a 100644
--- a/runtime/os.h
+++ b/runtime/os.h
@@ -35,7 +35,8 @@ class OS {
   // Open an existing file with read/write access.
   static File* OpenFileReadWrite(const char* name);
 
-  // Create an empty file with read/write access.
+  // Create an empty file with read/write access. This is a *new* file, that is, if the file
+  // already exists, it is *not* overwritten, but unlinked, and a new inode will be used.
   static File* CreateEmptyFile(const char* name);
 
   // Open a file with the specified open(2) flags.
diff --git a/runtime/os_linux.cc b/runtime/os_linux.cc
index 22827891b0..675699daea 100644
--- a/runtime/os_linux.cc
+++ b/runtime/os_linux.cc
@@ -36,6 +36,10 @@ File* OS::OpenFileReadWrite(const char* name) {
 }
 
 File* OS::CreateEmptyFile(const char* name) {
+  // In case the file exists, unlink it so we get a new file. This is necessary as the previous
+  // file may be in use and must not be changed.
+  unlink(name);
+
   return OpenFileWithFlags(name, O_RDWR | O_CREAT | O_TRUNC);
 }