[newlib-cygwin] newlib: ftello{64}: Handle appending stream without fflushing

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=6e5b39940ae95d098fb89cf80d48f6e03d3833bf

commit 6e5b39940ae95d098fb89cf80d48f6e03d3833bf
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Mon Dec 18 20:17:51 2017 +0100

    newlib: ftello{64}: Handle appending stream without fflushing
    
    Neither upstream FreeBSD nor glibc ever call fflush from ftell
    and friends.  In border cases it has the tendency to return
    wrong or unexpected values, for instance on block devices.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 newlib/libc/stdio/ftello.c     | 20 +++++++++++++-------
 newlib/libc/stdio64/ftello64.c | 20 +++++++++++++-------
 2 files changed, 26 insertions(+), 14 deletions(-)

diff --git a/newlib/libc/stdio/ftello.c b/newlib/libc/stdio/ftello.c
index 0a9bb7b..90c4d32 100644
--- a/newlib/libc/stdio/ftello.c
+++ b/newlib/libc/stdio/ftello.c
@@ -102,13 +102,19 @@ _DEFUN(_ftello_r, (ptr, fp),
       return (_off_t) -1;
     }
 
-  /* Find offset of underlying I/O object, then adjust for buffered
-     bytes.  Flush a write stream, since the offset may be altered if
-     the stream is appending.  Do not flush a read stream, since we
-     must not lose the ungetc buffer.  */
-  if (fp->_flags & __SWR)
-    _fflush_r (ptr, fp);
-  if (fp->_flags & __SOFF)
+  /* Find offset of underlying I/O object, then adjust for buffered bytes. */
+  if (!(fp->_flags & __SRD) && (fp->_flags & __SWR) &&
+      fp->_p != NULL && fp->_p - fp->_bf._base > 0 &&
+      (fp->_flags & __SAPP))
+    {
+      pos = fp->_seek (ptr, fp->_cookie, (_fpos_t) 0, SEEK_END);
+      if (pos == (_fpos_t) -1)
+	{
+          _newlib_flockfile_exit (fp);
+          return (_off_t) -1;
+	}
+    }
+  else if (fp->_flags & __SOFF)
     pos = fp->_offset;
   else
     {
diff --git a/newlib/libc/stdio64/ftello64.c b/newlib/libc/stdio64/ftello64.c
index 9aca231..2441d4c 100644
--- a/newlib/libc/stdio64/ftello64.c
+++ b/newlib/libc/stdio64/ftello64.c
@@ -99,13 +99,19 @@ _DEFUN (_ftello64_r, (ptr, fp),
       return (_off64_t) -1;
     }
 
-  /* Find offset of underlying I/O object, then adjust for buffered
-     bytes.  Flush a write stream, since the offset may be altered if
-     the stream is appending.  Do not flush a read stream, since we
-     must not lose the ungetc buffer.  */
-  if (fp->_flags & __SWR)
-    _fflush_r (ptr, fp);
-  if (fp->_flags & __SOFF)
+  /* Find offset of underlying I/O object, then adjust for buffered bytes. */
+  if (!(fp->_flags & __SRD) && (fp->_flags & __SWR) &&
+      fp->_p != NULL && fp->_p - fp->_bf._base > 0 &&
+      (fp->_flags & __SAPP))
+    {
+      pos = fp->_seek64 (ptr, fp->_cookie, (_fpos64_t) 0, SEEK_END);
+      if (pos == (_fpos64_t) -1)
+	{
+          _newlib_flockfile_exit (fp);
+          return (_off64_t) -1;
+	}
+    }
+  else if (fp->_flags & __SOFF)
     pos = fp->_offset;
   else
     {