src/java.base/unix/native/libnio/ch/FileDispatcherImpl.c

rev 16196 : 8168628: (fc) SIGBUS when extending file size to map it
Summary: Synchronize file extension and subsequent map0(); on Linux use fallocate64() instead of ftruncate64().
Reviewed-by: rehn, simonis, alanb

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this

@@ -184,10 +184,35 @@
     return handle(env,
                   ftruncate64(fdval(env, fdo), size),
                   "Truncation failed");
 }
 
+JNIEXPORT jint JNICALL
+Java_sun_nio_ch_FileDispatcherImpl_allocate0(JNIEnv *env, jobject this,
+                                             jobject fdo, jlong size)
+{
+    jint fd = fdval(env, fdo);
+#if defined(__linux__)
+    /*
+     * On Linux, if the file size is being increased, then ftruncate64()
+     * will modify the metadata value of the size without actually allocating
+     * any blocks which can cause a SIGBUS error if the file is subsequently
+     * memory-mapped.
+     */
+    struct stat64 fbuf;
+
+    if (fstat64(fd, &fbuf) == 0 && size > fbuf.st_blocks*512) {
+        return handle(env,
+                      fallocate64(fd, 0, 0, size),
+                      "Allocation failed");
+    }
+#endif
+    return handle(env,
+                  ftruncate64(fd, size),
+                  "Truncation failed");
+}
+
 JNIEXPORT jlong JNICALL
 Java_sun_nio_ch_FileDispatcherImpl_size0(JNIEnv *env, jobject this, jobject fdo)
 {
     jint fd = fdval(env, fdo);
     struct stat64 fbuf;