Documentation/console/console.txt

6 This type will be called 'system driver', and only one system driver is allowed
7 to exist. The system driver is persistent and it can never be unloaded, though
11 'modular driver' by this document. Multiple modular drivers can coexist at
12 any time with each driver sharing the console with other drivers including
13 the system driver. However, modular drivers cannot take over the console
14 that is currently occupied by another modular driver. (Exception: Drivers that
16 of driver occupying the consoles.) They can only take over the console that is
17 occupied by the system driver. In the same token, if the modular driver is
18 released by the console, the system driver will take over.
22 	 take_over_console() - load and bind driver to console layer
23 	 give_up_console() - unbind and unload driver
44      1. bind - this is a read/write file. It shows the status of the driver if
45         read, or acts to bind or unbind the driver to the virtual consoles
48 	0 - means the driver is not bound and if echo'ed, commands the driver
51         1 - means the driver is bound and if echo'ed, commands the driver to
54      2. name - read-only file. Shows the name of the driver in this format:
59 	    '(S)' stands for a (S)ystem driver, ie, it cannot be directly
62 	    'VGA+' is the name of the driver
67 	    In this case, '(M)' stands for a (M)odular driver, one that can be
72 When unbinding, the modular driver is detached first, and then the system
73 driver takes over the consoles vacated by the driver. Binding, on the other
74 hand, will bind the driver to the consoles that are currently occupied by a
75 system driver.
86 How useful is this feature? This is very useful for console driver
87 developers. By unbinding the driver from the console layer, one can unload the
88 driver, make changes, recompile, reload and rebind the driver without any need
102 give_up_console() is a wrapper to unregister_con_driver(), and a driver must
104 driver is bound or not.
106 Guidelines for console driver writers:
113    or take_over_console(). register_con_driver() will just add the driver to
122    driver, which was previously bound, becomes unbound.  The console layer
124    driver to check when it's legal to release these resources. Calling
128    rebind the driver to the console arrives.
130 4. Upon exit of the driver, ensure that the driver is totally unbound. If the
131    condition is satisfied, then the driver must call unregister_con_driver()
135    impossible for the driver to service console requests.  This can happen