fflush.3: Clarify that flushing of input streams occurs only for seekable files

See https://bugzilla.kernel.org/show_bug.cgi?id=91931

Reported-by: Sergey V. Zubkov <cubbi@cubbi.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man3/fflush.3 b/man3/fflush.3
index af7aff726669b3bd24ff8438ce9c41a0c990ab6f..90f8220dcfb17ecf37fde40da83c50d3e95678ca 100644 (file)
--- a/man3/fflush.3
+++ b/man3/fflush.3
@@ -55,10 +55,13 @@ For output streams,
 forces a write of all user-space buffered data for the given output or update
 .I stream
 via the stream's underlying write function.
-For input streams,
+
+For input streams associated with seekable files
+(e.g., disk files, but not pipes or terminals),
 .BR fflush ()
 discards any buffered data that has been fetched from the underlying file,
 but has not been consumed by the application.
+
 The open status of the stream is unaffected.
 .PP
 If the