Hi List,
I am a newbie and learning how to write a kernel module.
I was reading about __init qualifier, in the init.h file it is mentioned that:
/* These macros are used to mark some functions or
* initialized data (doesn't apply to uninitialized data)
* as `initialization' functions. The kernel can take this
* as hint that the function is used only during the initialization
* phase and free up used memory resources after
*
* Usage:
* For functions:
*
* You should add __init immediately before the function name, like:
*
* static void __init initme(int x, int y)
* {
* extern int z; z = x * y;
* }
*
* If the function has a prototype somewhere, you can also add
* __init between closing brace of the prototype and semicolon:
*
* extern int initialize_foobar_device(int, int, int) __init;
*
* For initialized data:
* You should insert __initdata between the variable name and equal
* sign followed by value, e.g.:
*
* static int init_variable __initdata = 0;
* static char linux_logo[] __initdata = { 0x32, 0x36, ... };
*
* Don't forget to initialize data not at file scope, i.e. within a function,
* as gcc otherwise puts the data into the bss section and not into the init
* section.
*
* Also note, that this data cannot be "const".
*/
I did not understand the purpose of __initdata qualifier?
1. Will the variable be free up after the initialization? Then it is
of no use to write the code like:
static int init_variable __initdata = 0;
Why I will initialize a variable and then free it?
2.
* Don't forget to initialize data not at file scope, i.e. within a function,
* as gcc otherwise puts the data into the bss section and not into the init
* section.
The above comment means that the __initdata can be used at functional
level variable only?
3.
* Also note, that this data cannot be "const".
Why the above restriction??
TIA,
Vijay
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