For "a"-mode files and rewind/fseek + fwrite combination return meaningful

value now, like Apple does, but avoid their __sflush physical write
performance degradation as much as possible.

1 files changed, 18 insertions, 0 deletions

diff --git a/lib/libc/stdio/ftell.c b/lib/libc/stdio/ftell.c
index 2c8800c..745d500 100644
--- a/lib/libc/stdio/ftell.c
+++ b/lib/libc/stdio/ftell.c
@@ -39,6 +39,7 @@ __FBSDID("$FreeBSD$");
 #include "namespace.h"
 #include <sys/types.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <limits.h>
 #include <stdio.h>
 #include "un-namespace.h"
@@ -87,6 +88,7 @@ _ftello(FILE *fp, fpos_t *offset)
 {
 	fpos_t pos;
 	size_t n;
+	int dflags;
 
 	if (fp->_seek == NULL) {
 		errno = ESPIPE;			/* historic practice */
@@ -118,6 +120,22 @@ _ftello(FILE *fp, fpos_t *offset)
 		if (HASUB(fp))
 			pos -= fp->_r;  /* Can be negative at this point. */
 	} else if ((fp->_flags & __SWR) && fp->_p != NULL) {
+		dflags = 0;
+		if (fp->_flags & __SAPP)
+			dflags = O_APPEND;
+		else if (fp->_file != -1 &&
+			 (dflags = _fcntl(fp->_file, F_GETFL)) < 0)
+			return (1);
+		if ((dflags & O_APPEND) &&
+		    (pos = _sseek(fp, (fpos_t)0, SEEK_END)) == -1) {
+			if ((fp->_flags & __SOPT) || __sflush(fp) ||
+			    (pos = _sseek(fp, (fpos_t)0, SEEK_CUR)) == -1)
+				return (1);
+			else {
+				*offset = pos;
+				return (0);
+			}
+		}
 		/*
 		 * Writing.  Any buffered characters cause the
 		 * position to be greater than that in the