commit e8b9e065a1ae9d7d8b888909ae761cbd5cf7be32

Author: Siddhesh Poyarekar <siddhesh@redhat.com>

Date:   Wed Mar 19 00:42:30 2014 +0530

    Fix offset computation for append+ mode on switching from read (BZ #16724)

    The offset computation in write mode uses the fact that _IO_read_end

    is kept in sync with the external file offset.  This however is not

    true when O_APPEND is in effect since switching to write mode ought to

    send the external file offset to the end of file without making the

    necessary adjustment to _IO_read_end.

    Hence in append mode, offset computation when writing should only

    consider the effect of unflushed writes, i.e. from _IO_write_base to

    _IO_write_ptr.

diff --git a/libio/Makefile b/libio/Makefile

index 69c25c0..4bedfad 100644

--- a/libio/Makefile

+++ b/libio/Makefile

@@ -60,7 +60,8 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc   \

 	tst-wmemstream1 tst-wmemstream2 \

 	bug-memstream1 bug-wmemstream1 \

 	tst-setvbuf1 tst-popen1 tst-fgetwc bug-wsetpos tst-fseek \

-	tst-fwrite-error tst-ftell-active-handler

+	tst-fwrite-error tst-ftell-active-handler \

+	tst-ftell-append

 ifeq (yes,$(build-shared))

 # Add test-fopenloc only if shared library is enabled since it depends on

 # shared localedata objects.

diff --git a/libio/fileops.c b/libio/fileops.c

index cf68dbf..204cfea 100644

--- a/libio/fileops.c

+++ b/libio/fileops.c

@@ -91,7 +91,9 @@ extern struct __gconv_trans_data __libio_translit attribute_hidden;

    The position in the buffer that corresponds to the position

    in external file system is normally _IO_read_end, except in putback

-   mode, when it is _IO_save_end.

+   mode, when it is _IO_save_end and also when the file is in append mode,

+   since switching from read to write mode automatically sends the position in

+   the external file system to the end of file.

    If the field _fb._offset is >= 0, it gives the offset in

    the file as a whole corresponding to eGptr(). (?)

@@ -966,6 +968,14 @@ do_ftell (_IO_FILE *fp)

       /* Adjust for unflushed data.  */

       if (!was_writing)

 	offset -= fp->_IO_read_end - fp->_IO_read_ptr;

+      /* We don't trust _IO_read_end to represent the current file offset when

+	 writing in append mode because the value would have to be shifted to

+	 the end of the file during a flush.  Use the write base instead, along

+	 with the new offset we got above when we did a seek to the end of the

+	 file.  */

+      else if (append_mode)

+	offset += fp->_IO_write_ptr - fp->_IO_write_base;

+      /* For all other modes, _IO_read_end represents the file offset.  */

       else

 	offset += fp->_IO_write_ptr - fp->_IO_read_end;

     }

diff --git a/libio/tst-ftell-append.c b/libio/tst-ftell-append.c

new file mode 100644

index 0000000..604dc03

--- /dev/null

+++ b/libio/tst-ftell-append.c

@@ -0,0 +1,169 @@

+/* Verify that ftell returns the correct value after a read and a write on a

+   file opened in a+ mode.

+   Copyright (C) 2014 Free Software Foundation, Inc.

+   This file is part of the GNU C Library.

+

+   The GNU C Library is free software; you can redistribute it and/or

+   modify it under the terms of the GNU Lesser General Public

+   License as published by the Free Software Foundation; either

+   version 2.1 of the License, or (at your option) any later version.

+

+   The GNU C Library is distributed in the hope that it will be useful,

+   but WITHOUT ANY WARRANTY; without even the implied warranty of

+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

+   Lesser General Public License for more details.

+

+   You should have received a copy of the GNU Lesser General Public

+   License along with the GNU C Library; if not, see

+   <http://www.gnu.org/licenses/>.  */

+

+#include <stdio.h>

+#include <stdlib.h>

+#include <string.h>

+#include <errno.h>

+#include <unistd.h>

+#include <locale.h>

+#include <wchar.h>

+

+/* data points to either char_data or wide_data, depending on whether we're

+   testing regular file mode or wide mode respectively.  Similarly,

+   fputs_func points to either fputs or fputws.  data_len keeps track of the

+   length of the current data and file_len maintains the current file

+   length.  */

+#define BUF_LEN 4

+static void *buf;

+static char char_buf[BUF_LEN];

+static wchar_t wide_buf[BUF_LEN];

+static const void *data;

+static const char *char_data = "abcdefghijklmnopqrstuvwxyz";

+static const wchar_t *wide_data = L"abcdefghijklmnopqrstuvwxyz";

+static size_t data_len;

+static size_t file_len;

+

+typedef int (*fputs_func_t) (const void *data, FILE *fp);

+fputs_func_t fputs_func;

+

+typedef void *(*fgets_func_t) (void *s, int size, FILE *stream);

+fgets_func_t fgets_func;

+

+static int do_test (void);

+

+#define TEST_FUNCTION do_test ()

+#include "../test-skeleton.c"

+

+static FILE *

+init_file (const char *filename)

+{

+  FILE *fp = fopen (filename, "w");

+  if (fp == NULL)

+    {

+      printf ("fopen: %m\n");

+      return NULL;

+    }

+

+  int written = fputs_func (data, fp);

+

+  if (written == EOF)

+    {

+      printf ("fputs failed to write data\n");

+      fclose (fp);

+      return NULL;

+    }

+

+  file_len = data_len;

+

+  fclose (fp);

+

+  fp = fopen (filename, "a+");

+  if (fp == NULL)

+    {

+      printf ("fopen(a+): %m\n");

+      return NULL;

+    }

+

+  return fp;

+}

+

+static int

+do_one_test (const char *filename)

+{

+  FILE *fp = init_file (filename);

+

+  if (fp == NULL)

+    return 1;

+

+  void *ret = fgets_func (buf, BUF_LEN, fp);

+

+  if (ret == NULL)

+    {

+      printf ("read failed: %m\n");

+      fclose (fp);

+      return 1;

+    }

+

+  int written = fputs_func (data, fp);

+

+  if (written == EOF)

+    {

+      printf ("fputs failed to write data\n");

+      fclose (fp);

+      return 1;

+    }

+

+  file_len += data_len;

+

+  long off = ftell (fp);

+

+  if (off != file_len)

+    {

+      printf ("Incorrect offset %ld, expected %zu\n", off, file_len);

+      fclose (fp);

+      return 1;

+    }

+  else

+    printf ("Correct offset %ld after write.\n", off);

+

+  return 0;

+}

+

+/* Run the tests for regular files and wide mode files.  */

+static int

+do_test (void)

+{

+  int ret = 0;

+  char *filename;

+  int fd = create_temp_file ("tst-ftell-append-tmp.", &filename);

+

+  if (fd == -1)

+    {

+      printf ("create_temp_file: %m\n");

+      return 1;

+    }

+

+  close (fd);

+

+  /* Tests for regular files.  */

+  puts ("Regular mode:");

+  fputs_func = (fputs_func_t) fputs;

+  fgets_func = (fgets_func_t) fgets;

+  data = char_data;

+  buf = char_buf;

+  data_len = strlen (char_data);

+  ret |= do_one_test (filename);

+

+  /* Tests for wide files.  */

+  puts ("Wide mode:");

+  if (setlocale (LC_ALL, "en_US.UTF-8") == NULL)

+    {

+      printf ("Cannot set en_US.UTF-8 locale.\n");

+      return 1;

+    }

+  fputs_func = (fputs_func_t) fputws;

+  fgets_func = (fgets_func_t) fgetws;

+  data = wide_data;

+  buf = wide_buf;

+  data_len = wcslen (wide_data);

+  ret |= do_one_test (filename);

+

+  return ret;

+}

diff --git a/libio/wfileops.c b/libio/wfileops.c

index 3199861..f123add 100644

--- a/libio/wfileops.c

+++ b/libio/wfileops.c

@@ -713,9 +713,16 @@ do_ftell_wide (_IO_FILE *fp)

 	      offset += outstop - out;

 	    }

-	  /* _IO_read_end coincides with fp._offset, so the actual file

-	     position is fp._offset - (_IO_read_end - new_write_ptr).  */

-	  offset -= fp->_IO_read_end - fp->_IO_write_ptr;

+	  /* We don't trust _IO_read_end to represent the current file offset

+	     when writing in append mode because the value would have to be

+	     shifted to the end of the file during a flush.  Use the write base

+	     instead, along with the new offset we got above when we did a seek

+	     to the end of the file.  */

+	  if (append_mode)

+	    offset += fp->_IO_write_ptr - fp->_IO_write_base;

+	  /* For all other modes, _IO_read_end represents the file offset.  */

+	  else

+	    offset += fp->_IO_write_ptr - fp->_IO_read_end;

 	}

     }