Re: [PING^8][PATCH v1.1] Fix offset computation for append+ mode on switching from read (BZ #16724)

[Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>]

Hi Siddhesh,

The patch look good, I would also add a point to 
https://sourceware.org/glibc/wiki/File%20offsets%20in%20a%20stdio%20stream%20and%20ftell
in commit message.


On 26-05-2014 03:08, Siddhesh Poyarekar wrote:
> Ping!
>
> On Thu, May 22, 2014 at 11:16:34AM +0530, Siddhesh Poyarekar wrote:
>> Ping!
>>
>> On Thu, May 15, 2014 at 02:09:27PM +0530, Siddhesh Poyarekar wrote:
>>> Ping!
>>>
>>> On Mon, Apr 28, 2014 at 08:20:01PM +0530, Siddhesh Poyarekar wrote:
>>>> Ping!
>>>>
>>>> On Tue, Apr 22, 2014 at 03:17:32PM +0530, Siddhesh Poyarekar wrote:
>>>>> Ping!
>>>>>
>>>>> On Fri, Apr 18, 2014 at 01:02:23PM +0530, Siddhesh Poyarekar wrote:
>>>>>> Ping!
>>>>>>
>>>>>> On Fri, Apr 11, 2014 at 03:11:12PM +0530, Siddhesh Poyarekar wrote:
>>>>>>> This fell off my ping radar, so...
>>>>>>>
>>>>>>> Ping!
>>>>>>>
>>>>>>> On Mon, Mar 24, 2014 at 09:21:38PM +0530, Siddhesh Poyarekar wrote:
>>>>>>>> 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
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>