Re: [PATCH] Do not break buffers in fvwrite for unbuffered files

[Corinna Vinschen <vinschen at redhat dot com>]

Hi Federico,

On Nov  1 10:39, Federico Terraneo wrote:
> On 10/31/2013 03:41 PM, Corinna Vinschen wrote:
> > On Oct 31 12:55, Federico Terraneo wrote:
> >> 
> >> This can't happen, since there's an
> >> 
> >> else if (fp->_p > fp->_bf._base || len < fp->_bf._size)
> >> 
> >> that catches this case and fills the file buffer instead.
> > 
> > Oh, hmm.  I didn't notice the || in the if clause.  Doesn't that
> > mean that the last else branch is never used since there's always a
> > buffer at _bf._base?  The fact that we use a FILE buffer is now
> > sufficient to use it and never to write directly, AFAICS.
> > 
> 
> Not exactly. The
> 
> if (fp->_p > fp->_bf._base
> 
> isn't true if there's a buffer. It's true if there is at least a
> character in the buffer, fp->_p is the 'put pointer'.
> [...]

Apparently I didn't wear my glasses because I misread the if clause.
Somehow I managed to read that as

  if (fp->_bf._base || len < fp->_bf._size)

entirely dropping the "fp->_p > ".  Sorry about that.

I checked the patch in with a minor change:

> -	  w = fp->_write (ptr, fp->_cookie, p, MIN (len, BUFSIZ));
> +	  w = fp->_write (ptr, fp->_cookie, p, MIN (len, INT_MAX));

I made that

          w = fp->_write (ptr, fp->_cookie, p,
                          MIN (len, INT_MAX - INT_MAX % BUFSIZ));

so the chunk is a multiple of BUFSIZ.


Thanks a lot,
Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat

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