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src/tests/vm/mmap-clean.c

+/* Verifies that mmap'd regions are only written back on munmap
+   if the data was actually modified in memory. */
+
+#include <string.h>
+#include <syscall.h>
+#include "tests/vm/sample.inc"
+#include "tests/lib.h"
+#include "tests/main.h"
+
+void
+test_main (void)
+{
+  static const char overwrite[] = "Now is the time for all good...";
+  static char buffer[sizeof sample - 1];
+  char *actual = (char *) 0x54321000;
+  int handle;
+  mapid_t map;
+
+  /* Open file, map, verify data. */
+  CHECK ((handle = open ("sample.txt")) > 1, "open \"sample.txt\"");
+  CHECK ((map = mmap (handle, actual)) != MAP_FAILED, "mmap \"sample.txt\"");
+  if (memcmp (actual, sample, strlen (sample)))
+    fail ("read of mmap'd file reported bad data");
+
+  /* Modify file. */
+  CHECK (write (handle, overwrite, strlen (overwrite))
+         == (int) strlen (overwrite),
+         "write \"sample.txt\"");
+
+  /* Close mapping.  Data should not be written back, because we
+     didn't modify it via the mapping. */
+  msg ("munmap \"sample.txt\"");
+  munmap (map);
+
+  /* Read file back. */
+  msg ("seek \"sample.txt\"");
+  seek (handle, 0);
+  CHECK (read (handle, buffer, sizeof buffer) == sizeof buffer,
+         "read \"sample.txt\"");
+
+  /* Verify that file overwrite worked. */
+  if (memcmp (buffer, overwrite, strlen (overwrite))
+      || memcmp (buffer + strlen (overwrite), sample + strlen (overwrite),
+                 strlen (sample) - strlen (overwrite))) 
+    {
+      if (!memcmp (buffer, sample, strlen (sample)))
+        fail ("munmap wrote back clean page");
+      else
+        fail ("read surprising data from file"); 
+    }
+  else
+    msg ("file change was retained after munmap");
+}