Re: address@hidden: Re: CVS commit: pkgsrc/devel/m4]

[Bruno Haible]

Joerg Sonnenberger wrote:
> Attached is a replacement version of fflush that is the least intrusive
> version I can think of. No further replacements for ftello/fseeko are
> needed. It should work with all BSD derived stdio implementations,
> directly tested are NetBSD and DragonFly.

Thanks for this idea. Eric, here is a proposed patch for gnulib, that
additionally:

  - uses the #ifdef for BSD systems,

  - not only sets __SNPT but also resets __SOPT. __SOPT tells fseek that
    it can use block-alignment as for regular files, __SNPT tells fseek
    that it must not do so. Since it is undocumented which of the two
    flags is tested first by fseek(), it is safer to reset __SOPT.

  - restores the previous flags after calling fseeko. Setting __SNPT
    means to disable block-aligned reading for *all* future fseek calls,
    but we need it only for the next one.

Tested on MacOS X.

If someone wants to submit a patch handling the __FILE_public, please do
"gnulib-tool --create-testdir --dir=... fbufmode fflush fpurge freadable \
 freading fseeko fseterr ftello fwritable fwriting"
to see which files need to be adjusted for this special situation.

Bruno


2007-07-27  Bruno Haible  <address@hidden>

        * lib/fflush.c (rpl_fflush): On BSD systems, use the __SNPT flag.
        Suggested by Joerg Sonnenberger <address@hidden>.

*** lib/fflush.c        27 Apr 2007 18:05:08 -0000      1.8
--- lib/fflush.c        27 Jul 2007 21:54:28 -0000
***************
*** 77,91 ****
    if (result != 0)
      return result;
  
    pos = lseek (fileno (stream), pos, SEEK_SET);
    if (pos == -1)
      return EOF;
    /* After a successful lseek, update the file descriptor's position cache
       in the stream.  */
! #if defined __sferror           /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin 
*/
    stream->_offset = pos;
    stream->_flags |= __SOFF;
! #endif
  
    return 0;
  }
--- 77,111 ----
    if (result != 0)
      return result;
  
+ #if defined __sferror && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, MacOS X, 
Cygwin */
+ 
+   {
+     /* Disable seek optimization for the next fseeko call.  This tells the
+        following fseeko call to seek to the desired position directly, rather
+        than to seek to a block-aligned boundary.  */
+     int saved_flags = stream->_flags & (__SOPT | __SNPT);
+     stream->_flags &= ~__SOPT;
+     stream->_flags |= __SNPT;
+ 
+     result = fseeko (stream, pos, SEEK_SET);
+ 
+     stream->_flags = (stream->_flags & ~(__SOPT | __SNPT)) | saved_flags;
+   }
+   return result;
+ 
+ #else
+ 
    pos = lseek (fileno (stream), pos, SEEK_SET);
    if (pos == -1)
      return EOF;
    /* After a successful lseek, update the file descriptor's position cache
       in the stream.  */
! # if defined __sferror           /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin 
*/
    stream->_offset = pos;
    stream->_flags |= __SOFF;
! # endif
  
    return 0;
+ 
+ #endif
  }