add instrumentation to detect some UMRs

src/tail.c

@@ -44,6 +44,21 @@
 #define AUTHORS \
   "Paul Rubin, David MacKenzie, Ian Lance Taylor, and Jim Meyering"
 
+#define MAGIC_BYTE 0xfa
+
+#define IS_MAGIC(x) 						\
+  ({								\
+    int _result = 0;						\
+    unsigned char *_p = (unsigned char *) &(x);			\
+    int _i;							\
+    for (_i = 0; _i < sizeof(x); _i++)				\
+      {								\
+	if (_p[_i] == MAGIC_BYTE)				\
+	  _result = 1;						\
+      }								\
+    _result;							\
+  })
+
 #ifndef ENOSYS
   /* Some systems don't have ENOSYS -- this should be a big enough
      value that no valid errno value will match it.  */
@@ -725,6 +740,8 @@ recheck (struct File_spec *f)
   int prev_errnum = f->errnum;
   int new_file;
 
+  assert (! IS_MAGIC (f->errnum));
+
   assert (valid_file_spec (f));
 
   fd = (is_stdin ? STDIN_FILENO : open (f->name, O_RDONLY));
@@ -785,7 +802,8 @@ recheck (struct File_spec *f)
       assert (f->fd == -1);
       error (0, 0, _("`%s' has become accessible"), pretty_name (f));
     }
-  else if (f->ino != new_stats.st_ino || f->dev != new_stats.st_dev)
+  else if ((assert (!IS_MAGIC (f->ino) && ! IS_MAGIC (f->dev)), 0)
+	   || f->ino != new_stats.st_ino || f->dev != new_stats.st_dev)  /* UMR */
     {
       new_file = 1;
       if (f->fd == -1)
@@ -877,7 +895,8 @@ tail_forever (struct File_spec *f, int nfiles)
 	{
 	  struct stat stats;
 
-	  if (f[i].ignore)
+	  assert (! IS_MAGIC (f[i].ignore));
+	  if (f[i].ignore)  /* UMR */
 	    continue;
 
 	  if (f[i].fd < 0)
@@ -1554,6 +1573,7 @@ main (int argc, char **argv)
     }
 
   F = (struct File_spec *) xmalloc (n_files * sizeof (F[0]));
+  memset (F, MAGIC_BYTE, n_files * sizeof (F[0]));
   for (i = 0; i < n_files; i++)
     F[i].name = file[i];