[PING][PATCH v1.1] Fix offset computation for append+ mode on switching from read (BZ #16724)

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

Ping!

On Wed, Mar 19, 2014 at 12:37:55PM +0530, Siddhesh Poyarekar wrote:
> The test case had a stupid error that got caught when I tested on
> powerpc.  Updated patch.
> 
> 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.
> 
> Tested on x86_64 (and not x86_66 like I mentioned earlier ;)), i686,
> s390 and ppc.
> 
> Siddhesh
> 
> 	[BZ #16724]
> 	* libio/tst-ftell-append.c: New test case.
> 	* libio/Makefile (tests): Add test case.
> 	* libio/fileops.c (do_ftell): Don't trust _IO_read_end when in
> 	append mode.
> 	* libio/wfileops.c (do_ftell_wide): Likewise.
> 
> ---
>  libio/Makefile           |   3 +-
>  libio/fileops.c          |  12 +++-
>  libio/tst-ftell-append.c | 169 +++++++++++++++++++++++++++++++++++++++++++++++
>  libio/wfileops.c         |  13 +++-
>  4 files changed, 192 insertions(+), 5 deletions(-)
>  create mode 100644 libio/tst-ftell-append.c
> 
> 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-partial-wide tst-ftell-active-handler
> +	tst-fwrite-error tst-ftell-partial-wide 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;
>  	}
>      }
>  
> -- 
> 1.8.3.1
>

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