mouse: Make /dev/mousein readable to get mouse status without blocking

There is currently no way to get the current mouse position
and button states without blocking.

1 files changed, 14 insertions, 7 deletions

diff --git a/sys/man/3/mouse b/sys/man/3/mouse
index 54e51d5ea..eda62cfab 100644
--- a/sys/man/3/mouse
+++ b/sys/man/3/mouse
@@ -56,23 +56,30 @@ Writes to the
 .B mousein
 file are processed as if they were generated by the
 mouse hardware itself,
-as extra mouse events to be processed and passed back via
-the
+as extra mouse events to be processed and passed back via the
 .B mouse
 file.
+Reading the
+.B mousein
+file returns the current mouse status without waiting.
 The
 .B mousein
 file, which may be opened
-only by the host owner, is intended for controlling devices, such as USB mice,
+only by the host owner, is intended for controlling devices,
+such as USB mice and tablets,
 that are managed by user-level software.
 Each event should consist of
 the letter
 .B m
-followed by delta
-.IR x ,
-delta
-.IR y ,
+(for relative delta coordinates)
+or
+.B A
+(for absolute screen coordinates)
+followed by the
+.I x
 and
+.I y
+coordinates and
 .IR buttons
 as space-separated decimal numbers.
 .PP