Re: [PATCH 2/2] libio: Fix seek-past-end returned size for open_{w}memstream (BZ#15298)

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 26/08/2016 07:14, Florian Weimer wrote:
> On 08/05/2016 07:40 PM, Adhemerval Zanella wrote:
>> +static _IO_off64_t
>> +_IO_wmem_seekoff (_IO_FILE *fp, _IO_off64_t offset, int dir, int mode)
>> +{
>> +  struct _IO_FILE_wmemstream *mp = (struct _IO_FILE_wmemstream *) fp;
>> +  if (fp->_wide_data->_IO_write_ptr != mp->seekwriteptr)
>> +    mp->prevwriteptr = fp->_wide_data->_IO_write_ptr;
>> +  _IO_off64_t ret = _IO_wstr_seekoff (fp, offset, dir, mode);
>> +  mp->seekwriteptr = fp->_wide_data->_IO_write_ptr;
>> +  return ret;
>> +}
> 
> As far as I can see, glibc will not call seekoff from the vfprintf code, ever, and _IO_wstr_jumps is only used for that.  This means the only actual use of _IO_wstr_seekoff is in the wmemstream code.  So you could rename/move _IO_wstr_seekoff and change it directly.  It should be fine to use a NULL pointer in _IO_wstr_jumops, just like _IO_obstack_jumps does.
> 

I though about moving both (while providing a compat symbol), but for consistency
I preferred to keep current code organization (so wmemstream and memstream would
be similar).

I see that a future cleanup on {w}memstream is possible, with a more simple
implementation.

> In contrast, _IO_str_seekoff is used from libstdc++ in GCC 2.95, so we cannot change it.
> 
> Florian
>