From a0d4bc1f98f8bdeb46a755598821b3d274277e30 Mon Sep 17 00:00:00 2001
From: Michael Kerrisk <mtk.manpages@gmail.com>
Date: Mon, 17 Dec 2007 14:52:20 +0000
Subject: [PATCH] Document VT_GETHIFONTMASK (new in 2.6.18) and add to example
 program; attribute/text characters are in the host byte order.

---
 man4/vcs.4 | 53 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 41 insertions(+), 12 deletions(-)

diff --git a/man4/vcs.4 b/man4/vcs.4
index e5831195f..6089f7ca8 100644
--- a/man4/vcs.4
+++ b/man4/vcs.4
@@ -22,8 +22,10 @@
 .\" USA.
 .\"
 .\" Modified, Sun Feb 26 15:08:05 1995, faith@cs.unc.edu
+.\" 2007-12-17, Samuel Thibault <samuel.thibault@ens-lyon.org>:
+.\"     document the VT_GETHIFONTMASK ioctl
 .\" "
-.TH VCS 4 1995-02-19 "Linux" "Linux Programmer's Manual"
+.TH VCS 4 2007-12-17 "Linux" "Linux Programmer's Manual"
 .SH NAME
 vcs, vcsa \- virtual console memory
 .SH DESCRIPTION
@@ -36,13 +38,26 @@ displayed virtual console terminal.
 terminals, they have major number 7 and minor number 1 to 63, usually
 mode 0644 and owner root.tty.
 \fI/dev/vcsa[0\-63]\fP are the same, but
-including attributes, and prefixed with four bytes giving the screen
+using unsigned shorts (in host byte order) that include attributes,
+and prefixed with four bytes giving the screen
 dimensions and cursor position: \fIlines\fP, \fIcolumns\fP, \fIx\fP, \fIy\fP.
 (\fIx\fP = \fIy\fP = 0 at the top left corner of the screen.)
+
+When a 512-character font is loaded,
+the 9th bit position can be fetched by applying the 
+.BR ioctl (2)
+\fBVT_GETHIFONTMASK\fP operation
+(available in Linux kernels 2.6.18 and above)
+on \fI/dev/tty[1\-63]\fP;
+the value is returned in the
+.I "unsigned short"
+pointed to by the third
+.BR ioctl (2)
+argument.
 .PP
-These replace the screendump
-.IR ioctl s
-of
+These devices replace the screendump
+.BR ioctl (2)
+operations of
 .BR console (4),
 so the system
 administrator can control access using file system permissions.
@@ -56,10 +71,6 @@ The devices for the first eight virtual consoles may be created by:
     done
     chown root:tty /dev/vcs*
 .fi
-
-No
-.BR ioctl (2)
-requests are supported.
 .SH FILES
 /dev/vcs[0\-63]
 .br
@@ -87,15 +98,30 @@ there:
 #include <stdlib.h>
 #include <stdio.h>
 #include <fcntl.h>
+#include <sys/ioctl.h>
+#include <linux/vt.h>
 
 int
 main(void)
 {
     int fd;
     char *device = "/dev/vcsa2";
+    char *console = "/dev/tty2";
     struct {unsigned char lines, cols, x, y;} scrn;
-    char ch, attrib;
+    unsigned short s;
+    unsigned short mask;
+    unsigned char ch, attrib;
 
+    fd = open(console, O_RDWR);
+    if (fd < 0) {
+        perror(console);
+        exit(EXIT_FAILURE);
+    }
+    if (ioctl(fd, VT_GETHIFONTMASK, &mask) < 0) {
+        perror("VT_GETHIFONTMASK");
+        exit(EXIT_FAILURE);
+    }
+    (void) close(fd);
     fd = open(device, O_RDWR);
     if (fd < 0) {
         perror(device);
@@ -103,8 +129,11 @@ main(void)
     }
     (void) read(fd, &scrn, 4);
     (void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), 0);
-    (void) read(fd, &ch, 1);
-    (void) read(fd, &attrib, 1);
+    (void) read(fd, &s, 2);
+    ch = s & 0xff;
+    if (attrib & mask)
+        ch |= 0x100;
+    attrib = ((s & ~mask) >> 8);
     printf("ch='%c' attrib=0x%02x\\n", ch, attrib);
     attrib ^= 0x10;
     (void) lseek(fd, \-1, 1);