Commit 6690075d authored by Antonino A. Daplas's avatar Antonino A. Daplas Committed by Linus Torvalds

[PATCH] VT binding: Update documentation

Update Documentation/fb/fbcon.txt and Documentatin/console/console.txt to
reflect the following changes:

1. sysfs attributes are relocated to /sys/class/vtconsole

2. feature is selectable in Kconfig

3. add sample scripts to fbcon.txt
Signed-off-by: default avatarAntonino Daplas <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 5bd42536
......@@ -27,45 +27,62 @@ In newer kernels, the following are also available:
If sysfs is enabled, the contents of /sys/class/tty/console/backend can be
examined. This shows the console drivers currently registered by the system. On
an x86 system with the framebuffer console enabled, the contents of this
attribute may be like this:
If sysfs is enabled, the contents of /sys/class/vtconsole can be
examined. This shows the console backends currently registered by the
system which are named vtcon<n> where <n> is an integer fro 0 to 15. Thus:
cat /sys/class/tty/console/backend
0 S: VGA+
1 B: frame buffer device
ls /sys/class/vtconsole
. .. vtcon0 vtcon1
The first line shows the VGA console driver, while the second line shows
the framebuffer console driver.
Each directory in /sys/class/vtconsole has 3 files:
The leftmost numeric character is the driver ID. The middle character with
the colon describes the status of the driver.
ls /sys/class/vtconsole/vtcon0
. .. bind name uevent
S: - system driver (binding unspecified)
B: - bound modular driver
U: - unbound modular driver
What do these files signify?
The last column is the description of the driver.
1. bind - this is a read/write file. It shows the status of the driver if
read, or acts to bind or unbind the driver to the virtual consoles
when written to. The possible values are:
Under /sys/class/tty/console are two other attributes, 'bind' and
'unbind'. What does these 2 attributes do? As their name implies, echo'ing the
driver ID to 'bind' will bind an unbound modular driver, and to 'unbind' will
unbind a bound modular driver. Echo'ing the ID of a system driver to either
attribute will do nothing.
0 - means the driver is not bound and if echo'ed, commands the driver
to unbind
1 - means the driver is bound and if echo'ed, commands the driver to
echo 1 > /sys/class/tty/console/unbind
cat /sys/class/tty/console/backend
0 S: VGA+
1 U: frame buffer device
2. name - read-only file. Shows the name of the driver in this format:
cat /sys/class/vtconsole/vtcon0/name
(S) VGA+
'(S)' stands for a (S)ystem driver, ie, it cannot be directly
commanded to bind or unbind
'VGA+' is the name of the driver
cat /sys/class/vtconsole/vtcon1/name
(M) frame buffer device
In this case, '(M)' stands for a (M)odular driver, one that can be
directly commanded to bind or unbind.
3. uevent - ignore this file
When unbinding, the modular driver is detached first, and then the system
driver takes over the consoles vacated by the driver. Binding, on the other
hand, will bind the driver to the consoles that are currently occupied by a
system driver.
NOTE1: Binding and binding must be selected in Kconfig. It's under:
Device Drivers -> Character devices -> Support for binding and unbinding
console drivers
NOTE2: If any of the virtual consoles are in KD_GRAPHICS mode, then binding or
unbinding will not succeed. An example of an application that sets the console
How useful is this feature? This is very useful for console driver
developers. By unbinding the driver from the console layer, one can unload the
driver, make changes, recompile, reload and rebind the driver without any need
......@@ -180,10 +180,13 @@ fbcon.
So, how do we unbind fbcon from the console? Part of the answer is in
Documentation/console/console.txt. To summarize:
Echo the ID number of the 'frame buffer driver' to:
Echo a value to the bind file that represents the framebuffer console
driver. So assuming vtcon1 represents fbcon, then:
sys/class/tty/console/bind - attach framebuffer console to console layer
sys/class/tty/console/unbind - detach framebuffer console from console layer
echo 1 > sys/class/vtconsole/vtcon1/bind - attach framebuffer console to
console layer
echo 0 > sys/class/vtconsole/vtcon1/bind - detach framebuffer console from
console layer
If fbcon is detached from the console layer, your boot console driver (which is
usually VGA text mode) will take over. A few drivers (rivafb and i810fb) will
......@@ -211,19 +214,15 @@ restored properly. The following is one of the several methods that you can do:
5. Now to detach fbcon:
'cat /sys/class/tty/console/backend' and take note of the ID
The above is probably needed only once. Then:
vbetool vbestate restore < <vga state file> && \
echo <ID> > /sys/class/tty/console/unbind
echo 0 > /sys/class/vtconsole/vtcon1/bind
6. That's it, you're back to VGA mode. And if you compiled fbcon as a module,
you can unload it by 'rmmod fbcon'
7. To reattach fbcon:
echo <ID> > /sys/class/tty/console/bind
echo 1 > /sys/class/vtconsole/vtcon1/bind
8. Once fbcon is unbound, all drivers registered to the system will also
become unbound. This means that fbcon and individual framebuffer drivers
......@@ -254,6 +253,8 @@ Variation 1:
c. Attach fbcon
vbetool vbestate restore < <vesa state file> && \
echo 1 > /sys/class/vtconsole/vtcon1/bind
Variation 2:
a. Before detaching fbcon, do:
......@@ -269,7 +270,55 @@ Variation 2:
c. Attach fbcon:
vbetool vbemode set <mode number> && \
echo <ID> > /sys/class/tty/console/bind
echo 1 > /sys/class/vtconsole/vtcon1/bind
Here are 2 sample bash scripts that you can use to bind or unbind the
framebuffer console driver if you are in an X86 box:
# Unbind fbcon
# Change this to where your actual vgastate file is located
# Or Use VGASTATE=$1 to indicate the state file at runtime
# path to vbetool
for (( i = 0; i < 16; i++))
if test -x /sys/class/vtconsole/vtcon$i; then
if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \
= 1 ]; then
if test -x $VBETOOL/vbetool; then
echo Unbinding vtcon$i
$VBETOOL/vbetool vbestate restore < $VGASTATE
echo 0 > /sys/class/vtconsole/vtcon$i/bind
# Bind fbcon
for (( i = 0; i < 16; i++))
if test -x /sys/class/vtconsole/vtcon$i; then
if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \
= 1 ]; then
echo Unbinding vtcon$i
echo 1 > /sys/class/vtconsole/vtcon$i/bind
Antonino Daplas <>
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