Bug 821168 - Use hardlinks for backing up pre-update files. r=eshan

toolkit/mozapps/update/updater/updater.cpp

@@ -82,6 +82,11 @@ void LaunchMacPostProcess(const char* aAppExe);
 
 #if defined(MOZ_WIDGET_GONK)
 # include "automounter_gonk.h"
+# include <unistd.h>
+# define MAYBE_USE_HARD_LINKS 1
+static bool sUseHardLinks = true;
+#else
+# define MAYBE_USE_HARD_LINKS 0
 #endif
 
 #ifdef XP_WIN
@@ -603,6 +608,25 @@ static int ensure_copy_symlink(const NS_tchar *path, const NS_tchar *dest)
 }
 #endif
 
+#if MAYBE_USE_HARD_LINKS
+/*
+ * Creates a hardlink (destFilename) which points to the existing file
+ * (srcFilename).
+ *
+ * @return 0 if successful, an error otherwise
+ */
+
+static int
+create_hard_link(const NS_tchar *srcFilename, const NS_tchar *destFilename)
+{
+  if (link(srcFilename, destFilename) < 0) {
+    LOG(("link(%s, %s) failed errno = %d", srcFilename, destFilename, errno));
+    return WRITE_ERROR;
+  }
+  return OK;
+}
+#endif
+
 // Copy the file named path onto a new file named dest.
 static int ensure_copy(const NS_tchar *path, const NS_tchar *dest)
 {
@@ -630,6 +654,16 @@ static int ensure_copy(const NS_tchar *path, const NS_tchar *dest)
   }
 #endif
 
+#if MAYBE_USE_HARD_LINKS
+  if (sUseHardLinks) {
+    if (!create_hard_link(path, dest)) {
+      return OK;
+    }
+    // Since we failed to create the hard link, fall through and copy the file.
+    sUseHardLinks = false;
+  }
+#endif
+
   AutoFile infile = ensure_open(path, NS_T("rb"), ss.st_mode);
   if (!infile) {
     LOG(("ensure_copy: failed to open the file for reading: " LOG_S ", err: %d",