Date: Wed, 26 Oct 1994 15:44:49 -0600

From: Chris Torek <torek@bsdi.com>
Here is a semi-official patch (apply to /usr/src/lib/libc/stdio/fseek.c,
rebuild libc, install).  The current code fails when the seek:

  - is optimized, and
  - is to just past the end of the block currently in the buffer, and
  - is followed by another seek with no intervening read operation, and
  - the destination of subsequent seek is within the block left in the
    buffer (seeking to the beginning of a block does not force a read,
    so the buffer still contains the previous block)

so it is indeed rather obscure.

I may have a different `final' fix, as this one `loses' the buffer
contents on a seek that goes just past the end of the current block.

[Footnote: seeks are optimized only on read-only opens of regular
files that are buffered by the file's optimal I/O size.  This is
what you get with fopen(path, "r") and no call to setvbuf().]

Obtained from: [ BSDI mailing list ]

lib/libc/stdio/fseek.c

@@ -213,6 +213,7 @@ fseek(fp, offset, whence)
 	if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
 		goto dumb;
 	fp->_r = 0;
+	fp->_p = fp->_bf._base;
 	if (HASUB(fp))
 		FREEUB(fp);
 	fp->_flags &= ~__SEOF;