[PATCH] Fix ftell/ungetc

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

If ftell{,o,o64} is called after ungetc while the FILE is still in backup,
but fp->_offset is _IO_pos_BAD, ftell{,o,o64} destroys the backup (which
it shouldn't) and returns bogus offset.
I think markers etc. don't need to be killed on mode == 0 seekoff
(which is just querying current offset, not moving in any way).
I'm not 100% sure it is ok to set fp->_offset, but I hope it is.

2004-11-04  Jakub Jelinek  <jakub@redhat.com>

	* libio/fileops.c (_IO_new_file_seekoff): If mode is 0 and
	fp->_offset == _IO_pos_BAD, just call _IO_SYSSEEK (fp, 0, dir)
	and if successful set fp->_offset.
	* libio/Makefile (tests): Add bug-ungetc3.
	* libio/bug-ungetc3.c: New test.

--- libc/libio/fileops.c.jj	2004-09-16 11:35:19.000000000 +0200
+++ libc/libio/fileops.c	2004-11-04 10:59:31.733498422 +0100
@@ -989,7 +989,18 @@ _IO_new_file_seekoff (fp, offset, dir, m
       /* Adjust for read-ahead (bytes is buffer). */
       offset -= fp->_IO_read_end - fp->_IO_read_ptr;
       if (fp->_offset == _IO_pos_BAD)
-	goto dumb;
+        {
+          if (mode != 0)
+            goto dumb;
+          else
+            {
+              result = _IO_SYSSEEK (fp, 0, dir);
+              if (result == EOF)
+                return result;
+
+              fp->_offset = result;
+            }
+        }
       /* Make offset absolute, assuming current pointer is file_ptr(). */
       offset += fp->_offset;
       if (offset < 0)
--- libc/libio/Makefile.jj	2004-10-18 10:20:45.000000000 +0200
+++ libc/libio/Makefile	2004-11-04 11:08:04.905149675 +0100
@@ -54,7 +54,7 @@ tests = tst_swprintf tst_wprintf tst_sws
 	tst-freopen bug-rewind bug-rewind2 bug-ungetc bug-fseek \
 	tst-mmap-eofsync tst-mmap-fflushsync bug-mmap-fflush \
 	tst-mmap2-eofsync tst-mmap-offend bug-fopena+ bug-wfflush \
-	bug-ungetc2 bug-ftell
+	bug-ungetc2 bug-ftell bug-ungetc3
 test-srcs = test-freopen
 
 all: # Make this the default target; it will be defined in Rules.
--- libc/libio/bug-ungetc3.c.jj	2004-11-03 22:48:05.000000000 +0100
+++ libc/libio/bug-ungetc3.c	2004-11-04 11:06:14.322832754 +0100
@@ -0,0 +1,94 @@
+/* Test program for ungetc/ftell interaction bug.  */
+
+#include <stdio.h>
+
+static void do_prepare (void);
+#define PREPARE(argc, argv) do_prepare ()
+static int do_test (void);
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
+
+static const char pattern[] = "12345";
+static char *temp_file;
+
+static void
+do_prepare (void)
+{
+  int fd = create_temp_file ("bug-ungetc.", &temp_file);
+  if (fd == -1)
+    {
+      printf ("cannot create temporary file: %m\n");
+      exit (1);
+    }
+  write (fd, pattern, sizeof (pattern));
+  close (fd);
+}
+
+static int
+do_one_test (int mode)
+{
+  FILE *f;
+
+  f = fopen (temp_file, "r");
+  if (f == NULL)
+    {
+      printf ("could not open temporary file: %m\n");
+      return 1;
+    }
+
+  if (mode == 1 && ftell (f) != 0)
+    {
+      printf ("first ftell returned wrong position %ld\n", ftell (f));
+      return 1;
+    }
+
+  if (fgetc (f) != '1' || fgetc (f) != '2')
+    {
+      puts ("fgetc failed");
+      return 1;
+    }
+
+  if (mode == 2 && ftell (f) != 2)
+    {
+      printf ("second ftell returned wrong position %ld\n", ftell (f));
+      return 1;
+    }
+
+  if (ungetc ('6', f) != '6')
+    {
+      puts ("ungetc failed");
+      return 1;
+    }
+
+  if (ftell (f) != 1)
+    {
+      printf ("third ftell returned wrong position %ld\n", ftell (f));
+      return 1;
+    }
+
+  if (fgetc (f) != '6')
+    {
+      puts ("fgetc failed");
+      return 1;
+    }
+
+  if (ftell (f) != 2)
+    {
+      printf ("fourth ftell returned wrong position %ld\n", ftell (f));
+      return 1;
+    }
+
+  fclose (f);
+
+  return 0;
+}
+
+static int
+do_test (void)
+{
+  int mode;
+  for (mode = 0; mode <= 2; mode++)
+    if (do_one_test (mode))
+      return 1;
+  return 0;
+}

	Jakub