[PATCH v2 4/4] man/man3/termios.3: document that cfsetispeed(..., 0) is deprecated

POSIX.1-2024 deprecated cfsetispeed(..., 0). This was always rather
confusing, since all other uses of speed_t use the Bnnn symbolic
constants, although B0 == 0 was largely universal.

Document that setting the input speed to numeric-zero meaning the same
as the output speed is deprecated, and applications should explicitly
set it to the same value as the output baud rate instead.

Signed-off-by: H. Peter Anvin <[email protected]>
---
 man/man3/termios.3 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/man/man3/termios.3 b/man/man3/termios.3
index 84b10cb7d68c..9a606e689e80 100644
--- a/man/man3/termios.3
+++ b/man/man3/termios.3
@@ -1182,6 +1182,9 @@ even when using
 the input baud rate
 will be equal to the output baud rate.
 .P
+POSIX.1-2024 deprecated this; new code should explicitly set both the
+input and output baud rates to the same value.
+.P
 .BR cfsetspeed ()
 is a 4.4BSD extension.
 It takes the same arguments as
-- 
2.54.0