Re: some basic doubts / confusion regarding linux kernel / OS

[Mandeep Sandhu <mandeepsandhu.chd@xxxxxxxxx>]

On Thu, Oct 3, 2013 at 10:38 PM, ajay saini <ajay_saini1006@xxxxxxxxxxx> wrote:

Hi,

I had some confusion/doubts regarding Linux kernel / OS and I want to be completely sure that my understanding is right for below, and need your inputs (would be really glad for your help):

- There are functions defined in linux kernel. Some of these functions have a line "EXPORT_SYMBOL(<function_name>);"  after them.

   These are the functions which are exported, so they can be directly called from a linux kernel module - right ? (we just need to include header files which define

   them in our kernel module)

Yes. They are used during dynamic loading of modules. More here: http://stackoverflow.com/questions/6670589/use-of-export-symbol

 

- There are some functions defined in linux kernel, which are not static and are not exported, like "migrate_pages" in migrate.c and it is mentioned in

   include/linux/migrate.h file. 

   Is there a way to call these functions, directly from kernel module ?? (even if I include the header file) ??

   If no, What is the technique used there, which prevents the module from calling this function (even though I have included the header file)??

The  compiler? :)

- We have kernel header files defined in include/linux/ and there are user space header files (the C libraries).

    Can a user space program include kernel header file and call a kernel function directly?? No , right ??

    Again, what is there which prevents a user space program from doing so?? How this technique is implemented ??

Kernel fxn's can't be called directly, you'll have to use either the syscal interface or one of the many (indirect) userspace-kernel communication mechanisms.

Again, the "technique" here is that you compiler will barf if you try and use kernel functions directly as it won't find the definitions of those functions during linking. CMIIW.

HTH,

-mandeep

   

- I understand that, a struct page exists for each physical page in RAM. And this linked list of struct pages are stored together at the beginning of a zone. After this

  storage, does the real data (content) of pages is stored.

  Now each of these pages must be pointing to the data area/page which they define ? Which is this field in the struct page, which points to this data area, a physical

  address + length of the page ?

   

Thanks,

Ajay

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies