---

yaml
---
r: 30431
b: refs/heads/master
c: 61a46dc
h: refs/heads/master
i:
  30429: 4ff6b01
  30427: 1416822
  30423: 5fbcb52
  30415: cd5d09b
  30399: 1779126
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 8070b2b1ecbeb5437c92c33b4dcea1d8d80399ee
+refs/heads/master: 61a46dc9d1c10d07a2ed6b7d346b868803b52506

trunk/Documentation/console/console.txt

@@ -0,0 +1,144 @@
+Console Drivers
+===============
+
+The linux kernel has 2 general types of console drivers.  The first type is
+assigned by the kernel to all the virtual consoles during the boot process.
+This type will be called 'system driver', and only one system driver is allowed
+to exist. The system driver is persistent and it can never be unloaded, though
+it may become inactive.
+
+The second type has to be explicitly loaded and unloaded. This will be called
+'modular driver' by this document. Multiple modular drivers can coexist at
+any time with each driver sharing the console with other drivers including
+the system driver. However, modular drivers cannot take over the console
+that is currently occupied by another modular driver. (Exception: Drivers that
+call take_over_console() will succeed in the takeover regardless of the type
+of driver occupying the consoles.) They can only take over the console that is
+occupied by the system driver. In the same token, if the modular driver is
+released by the console, the system driver will take over.
+
+Modular drivers, from the programmer's point of view, has to call:
+
+	 take_over_console() - load and bind driver to console layer
+	 give_up_console() - unbind and unload driver
+
+In newer kernels, the following are also available:
+
+	 register_con_driver()
+	 unregister_con_driver()
+
+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:
+
+       ls /sys/class/vtconsole
+       .  ..  vtcon0  vtcon1
+
+Each directory in /sys/class/vtconsole has 3 files:
+
+     ls /sys/class/vtconsole/vtcon0
+     .  ..  bind  name  uevent
+
+What do these files signify?
+
+     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:
+
+	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
+	    bind
+
+     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
+to KD_GRAPHICS is X.
+
+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
+for rebooting the kernel. For regular users who may want to switch from
+framebuffer console to VGA console and vice versa, this feature also makes
+this possible. (NOTE NOTE NOTE: Please read fbcon.txt under Documentation/fb
+for more details).
+
+Notes for developers:
+=====================
+
+take_over_console() is now broken up into:
+
+     register_con_driver()
+     bind_con_driver() - private function
+
+give_up_console() is a wrapper to unregister_con_driver(), and a driver must
+be fully unbound for this call to succeed. con_is_bound() will check if the
+driver is bound or not.
+
+Guidelines for console driver writers:
+=====================================
+
+In order for binding to and unbinding from the console to properly work,
+console drivers must follow these guidelines:
+
+1. All drivers, except system drivers, must call either register_con_driver()
+   or take_over_console(). register_con_driver() will just add the driver to
+   the console's internal list. It won't take over the
+   console. take_over_console(), as it name implies, will also take over (or
+   bind to) the console.
+
+2. All resources allocated during con->con_init() must be released in
+   con->con_deinit().
+
+3. All resources allocated in con->con_startup() must be released when the
+   driver, which was previously bound, becomes unbound.  The console layer
+   does not have a complementary call to con->con_startup() so it's up to the
+   driver to check when it's legal to release these resources. Calling
+   con_is_bound() in con->con_deinit() will help.  If the call returned
+   false(), then it's safe to release the resources.  This balance has to be
+   ensured because con->con_startup() can be called again when a request to
+   rebind the driver to the console arrives.
+
+4. Upon exit of the driver, ensure that the driver is totally unbound. If the
+   condition is satisfied, then the driver must call unregister_con_driver()
+   or give_up_console().
+
+5. unregister_con_driver() can also be called on conditions which make it
+   impossible for the driver to service console requests.  This can happen
+   with the framebuffer console that suddenly lost all of its drivers.
+
+The current crop of console drivers should still work correctly, but binding
+and unbinding them may cause problems. With minimal fixes, these drivers can
+be made to work correctly.
+
+==========================
+Antonino Daplas <adaplas@pol.net>
+

trunk/Documentation/fb/fbcon.txt

@@ -135,10 +135,10 @@ C. Boot options
 
 	The angle can be changed anytime afterwards by 'echoing' the same
 	numbers to any one of the 2 attributes found in
-	/sys/class/graphics/fb{x}
+	 /sys/class/graphics/fbcon
 
-		con_rotate     - rotate the display of the active console
-		con_rotate_all - rotate the display of all consoles
+		rotate     - rotate the display of the active console
+		rotate_all - rotate the display of all consoles
 
 	Console rotation will only become available if Console Rotation
 	Support is compiled in your kernel.
@@ -148,5 +148,177 @@ C. Boot options
 	Actually, the underlying fb driver is totally ignorant of console
 	rotation.
 
----
+C. Attaching, Detaching and Unloading
+
+Before going on on how to attach, detach and unload the framebuffer console, an
+illustration of the dependencies may help.
+
+The console layer, as with most subsystems, needs a driver that interfaces with
+the hardware. Thus, in a VGA console:
+
+console ---> VGA driver ---> hardware.
+
+Assuming the VGA driver can be unloaded, one must first unbind the VGA driver
+from the console layer before unloading the driver.  The VGA driver cannot be
+unloaded if it is still bound to the console layer. (See
+Documentation/console/console.txt for more information).
+
+This is more complicated in the case of the the framebuffer console (fbcon),
+because fbcon is an intermediate layer between the console and the drivers:
+
+console ---> fbcon ---> fbdev drivers ---> hardware
+
+The fbdev drivers cannot be unloaded if it's bound to fbcon, and fbcon cannot
+be unloaded if it's bound to the console layer.
+
+So to unload the fbdev drivers, one must first unbind fbcon from the console,
+then unbind the fbdev drivers from fbcon.  Fortunately, unbinding fbcon from
+the console layer will automatically unbind framebuffer drivers from
+fbcon. Thus, there is no need to explicitly unbind the fbdev drivers from
+fbcon.
+
+So, how do we unbind fbcon from the console? Part of the answer is in
+Documentation/console/console.txt. To summarize:
+
+Echo a value to the bind file that represents the framebuffer console
+driver. So assuming vtcon1 represents fbcon, then:
+
+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
+restore VGA text mode for you.  With the rest, before detaching fbcon, you
+must take a few additional steps to make sure that your VGA text mode is
+restored properly. The following is one of the several methods that you can do:
+
+1. Download or install vbetool.  This utility is included with most
+   distributions nowadays, and is usually part of the suspend/resume tool.
+
+2. In your kernel configuration, ensure that CONFIG_FRAMEBUFFER_CONSOLE is set
+   to 'y' or 'm'. Enable one or more of your favorite framebuffer drivers.
+
+3. Boot into text mode and as root run:
+
+	vbetool vbestate save > <vga state file>
+
+	The above command saves the register contents of your graphics
+	hardware to <vga state file>.  You need to do this step only once as
+	the state file can be reused.
+
+4. If fbcon is compiled as a module, load fbcon by doing:
+
+       modprobe fbcon
+
+5. Now to detach fbcon:
+
+       vbetool vbestate restore < <vga state file> && \
+       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 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
+can be unloaded or reloaded at will. Reloading the drivers or fbcon will
+automatically bind the console, fbcon and the drivers together. Unloading
+all the drivers without unloading fbcon will make it impossible for the
+console to bind fbcon.
+
+Notes for vesafb users:
+=======================
+
+Unfortunately, if your bootline includes a vga=xxx parameter that sets the
+hardware in graphics mode, such as when loading vesafb, vgacon will not load.
+Instead, vgacon will replace the default boot console with dummycon, and you
+won't get any display after detaching fbcon. Your machine is still alive, so
+you can reattach vesafb. However, to reattach vesafb, you need to do one of
+the following:
+
+Variation 1:
+
+    a. Before detaching fbcon, do
+
+       vbetool vbemode save > <vesa state file> # do once for each vesafb mode,
+						# the file can be reused
+
+    b. Detach fbcon as in step 5.
+
+    c. Attach fbcon
+
+        vbetool vbestate restore < <vesa state file> && \
+	echo 1 > /sys/class/vtconsole/vtcon1/bind
+
+Variation 2:
+
+    a. Before detaching fbcon, do:
+	echo <ID> > /sys/class/tty/console/bind
+
+
+       vbetool vbemode get
+
+    b. Take note of the mode number
+
+    b. Detach fbcon as in step 5.
+
+    c. Attach fbcon:
+
+       vbetool vbemode set <mode number> && \
+       echo 1 > /sys/class/vtconsole/vtcon1/bind
+
+Samples:
+========
+
+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:
+
+---------------------------------------------------------------------------
+#!/bin/bash
+# Unbind fbcon
+
+# Change this to where your actual vgastate file is located
+# Or Use VGASTATE=$1 to indicate the state file at runtime
+VGASTATE=/tmp/vgastate
+
+# path to vbetool
+VBETOOL=/usr/local/bin
+
+
+for (( i = 0; i < 16; i++))
+do
+  if test -x /sys/class/vtconsole/vtcon$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
+	    fi
+      fi
+  fi
+done
+
+---------------------------------------------------------------------------
+#!/bin/bash
+# Bind fbcon
+
+for (( i = 0; i < 16; i++))
+do
+  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
+      fi
+  fi
+done
+---------------------------------------------------------------------------
+
+--
 Antonino Daplas <adaplas@pol.net>

trunk/Documentation/filesystems/ext3.txt

@@ -113,6 +113,14 @@ noquota
 grpquota
 usrquota
 
+bh		(*)	ext3 associates buffer heads to data pages to
+nobh			(a) cache disk block mapping information
+			(b) link pages into transaction to provide
+			    ordering guarantees.
+			"bh" option forces use of buffer heads.
+			"nobh" option tries to avoid associating buffer
+			heads (supported only for "writeback" mode).
+
 
 Specification
 =============