December 2012 - kernelnewbies@kernelnewbies.org

Accessing serial port from kernel space
by Tcendrovskii Vladislav Dec. 16, 2012

Dec. 16, 2012

Hello! I need to access serial port from my module. But I haven't found functions to access it. And as i understood, all work with serial port goes through TTY system. So, if it exist some documentation on this system, and how can i use it from kernel space? In tty.txt i've found only line discipline, which is not, what i need.

2 1

Re: Locating the keyboard driver (and replacing it)
by Anuz Pratap Singh Tomar Dec. 14, 2012

Dec. 14, 2012

On Fri, Dec 14, 2012 at 11:31 AM, Anuz Pratap Singh Tomar < chambilkethakur(a)gmail.com> wrote: > > > On Fri, Dec 14, 2012 at 10:27 AM, manty kuma <mantykuma(a)gmail.com> wrote: > >> Hi Sannu, >> I tried grepping lsmod with kdb. It doesnt show anything. >> >> Regards, >> Manty >> >> >> On Fri, Dec 14, 2012 at 2:07 PM, Sannu K <sannumail4foss(a)gmail.com>wrote: >> >>> Try grepping for kdb. I have not tried this, just a suggestion. >>> >>> Hope this helps, >>> Sannu K >>> >>> On Fri, Dec 14, 2012 at 1:16 PM, manty kuma <mantykuma(a)gmail.com> wrote: >>> > Hi, >>> > >>> > I have written a small module that toggles the capslock LED. To >>> demonstrate >>> > it i want to replace the Existing keyboard module with mine. I tried >>> > lsmod|grep "key" without any success. also checked /proc/modules. I >>> couldnot >>> > find any clue regarding the name of the module i need to uninstall. >>> So, How >>> > can i remove the existing keyboard module and insert mine? >>> > >>> > Regards, >>> > Manty >>> > >>> >> I am be very sure(and thus please verify all of it), but I think keyboard > drivers are statically compiled and they are tied to tty consoles. > you may have to use one of the other testing mechanism like virtualization > i.e. use usermode linux etc and compile your module along with they > keyboard driver because keyboard drivers come up very early in booting > process. > > Please read it as "I am _NOT_"

1 0

Re: Asking another process sleep from another process or interrupt context
by Grzegorz Dwornicki Dec. 14, 2012

Dec. 14, 2012

Hi I have to ask about this: can process ignore this signal? If yes then this method is not perfect. I know i read somewhere about signals and there was this part: processes can ignore nearly all of them. Two signals can't be ignored: SIGKILL and... I don't remember the second... Greg.

1 0

Re: insmod: error inserting 'test2.ko': -1 Unknown symbol in module
by Grzegorz Dwornicki Dec. 14, 2012

Dec. 14, 2012

Well I had same problem in my own project that I am working ATM. We won't be sure what is wrong until you show us the sourcecode but my guess is missing EXPORT_SYMBOL makro - that was missing in my project. Greg. ----- Reply message ----- From: "Pritam Bankar" <pritambankar1988 at gmail.com> Date: Mon, Dec 3, 2012 12:18 pm Subject: insmod: error inserting 'test2.ko': -1 Unknown symbol in module To: "kernelnewbies" <kernelnewbies at kernelnewbies.org> Hi, What is basic reason behind error "Unknown symbol in module" ? I have two modules test1.ko and test2.ko. test1.ko loads succesfully but test2.ko gives error insmod: error inserting 'test2.ko': -1 Unknown symbol in module dmesg shows all symbols in module as unknown. To give more details I have compiled both modules same way with same compiler options and with modpost, Module.Symvers files. Another point to mention is that both modules load perfectly on 2.6 kernel. But kernel on which I am trying is 3.0 series kernel. What can be entry point to look into this issue ? Thanks, Pritam

1 0

can I input a gate service to kernel to get kernel data to user ?
by horse_rivers Dec. 14, 2012

Dec. 14, 2012

is there method for doing this work? take kernel data to user? thanks!

3 5

Re: can I input a gate service to kernel to get kernel data to user ?
by jeshkumar555＠gmail.com Dec. 14, 2012

Dec. 14, 2012

Hello :), Refer this doc for user and kernel communication methods. Hope it helps :). people.ee.ethz.ch/~arkeller/linux/multi/kernel_user_space_howto.html#toc2 Sent from my HTC Excuse for typo. ----- Reply message ----- From: "horse_rivers" <horse_rivers(a)126.com> Date: Fri, Dec 14, 2012 6:29 am Subject: can I input a gate service to kernel to get kernel data to user ? To: "kernelnewbies(a)kernelnewbies.org" <kernelnewbies(a)kernelnewbies.org> At 2012-12-13 18:11:24,"Daniel Baluta" <daniel.baluta(a)gmail.com> wrote: >On Thu, Dec 13, 2012 at 5:17 AM, horse_rivers <horse_rivers(a)126.com> wrote: >> is there method for doing this work? take kernel data to user? > >Check copy_to_user [1]. how can user application achive to getting data from kernel , I have no idea about procedure for implementing this quest is there some advice ? BestRegards! > >thanks, >Daniel. > >[1] http://lxr.linux.no/#linux+v3.7/arch/x86/lib/usercopy_32.c#L715 > >_______________________________________________ >Kernelnewbies mailing list >Kernelnewbies(a)kernelnewbies.org >http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

1 0

QoS Kernel Implementation
by Pietro Paolini Dec. 13, 2012

Dec. 13, 2012

Hi all, I am going to study the Linux implementation of the QoS on the Linux kernel, could someone give me some link at documents, papers... I am googling the problem but I think that in this newsletter there are a lot of competent people who can suggest me the right way! Best Regards, Pietro Paolini.

2 1

multicasting as a server and listening as a client?
by devendra.aaru Dec. 13, 2012

Dec. 13, 2012

Hello, i have a problem where in i have to use a server, which multicasts packets to all the clients over a port upon a specified event, on lo multicast address, and also accept requests from the clients. i just tried this multicast approach because if i use tcp for this there will be more clients to handle for the server. but seems that as the generic rules of server and client clients can't recieve multicast packets as they didn't bind to the port where in which the server is sending the packets. is there anyway i can solve this. please help!

1 0

Why do { // do something ; } while (0); ?
by Shraddha Kamat Dec. 13, 2012

Dec. 13, 2012

I notice do { // do something 1 ; // do something 2 ; ... } while (0); being used everywhere in the kernel code I just can't guess of any use of this other than executing couple of C statements together ? Is there any special purpose of doing this ?? Sorry of such a silly question - I am just trying to learn kernel hacking basics. -- Shraddha

3 2

Find out function arguments value from stack pointer
by Manavendra Nath Manav Dec. 12, 2012

Dec. 12, 2012

Given stack pointer value, is it possible to determine the value of the passed arguments to the function? Where are the arguments stored in the stack frame. Lets say, executing gcc compiled ELF binary on x86 architecture on Linux platform: int foo(int a, int b) { ... } foo(a,b) is called from main() and I know the stack pointer(SP) value which is pointing to foo() now. How can I retrive the value of arguments a and b? If stack grows from smaller address to larger address, and arguments are passed right to left usingcdecl, can I obtain args value like this: b = *(SP + 1); a = *(SP + 2); The following program prints the value of functions args a, b using above arch and specifications. void foo(int a, int b) { int i; register int stackptr asm("sp"); int *sp = (int *)stackptr; printf("\n\ta=%d b=%d\n", a, b); for (i=0; i<16; i++) { printf("*(sp + %d) = %d\n", i, *(sp +i)); } } int main() { foo(3, 8); foo(9, 2); foo(1, 4); return 0; } The output of above code is: a=3 b=8 *(sp + 0) = 134514016 *(sp + 1) = 0 *(sp + 2) = 0 *(sp + 3) = 134513373 *(sp + 4) = 8239384 *(sp + 5) = 134513228 *(sp + 6) = 6 *(sp + 7) = -1076716032 *(sp + 8) = 134513456 *(sp + 9) = 0 *(sp + 10) = -1076715960 *(sp + 11) = 134513759 *(sp + 12) = 3 //value of arg a *(sp + 13) = 8 //value of arg b *(sp + 14) = 134513817 *(sp + 15) = 10612724 a=9 b=2 *(sp + 0) = 134514016 *(sp + 1) = 0 *(sp + 2) = 0 *(sp + 3) = 134513373 *(sp + 4) = 8239384 *(sp + 5) = 134513228 *(sp + 6) = 6 *(sp + 7) = -1076716032 *(sp + 8) = 134513456 *(sp + 9) = 0 *(sp + 10) = -1076715960 *(sp + 11) = 134513779 *(sp + 12) = 9 //value of arg a *(sp + 13) = 2 //value of arg b *(sp + 14) = 134513817 *(sp + 15) = 10612724 a=1 b=4 *(sp + 0) = 134514016 *(sp + 1) = 0 *(sp + 2) = 0 *(sp + 3) = 134513373 *(sp + 4) = 8239384 *(sp + 5) = 134513228 *(sp + 6) = 6 *(sp + 7) = -1076716032 *(sp + 8) = 134513456 *(sp + 9) = 0 *(sp + 10) = -1076715960 *(sp + 11) = 134513799 *(sp + 12) = 1 //value of arg a *(sp + 13) = 4 //value of arg b *(sp + 14) = 134513817 *(sp + 15) = 10612724 Why function arguments are stored from offset 12 of SP? Also notice values at offset 0 to 10 are always same, and value at offset 11 increases by 20 on each invocation of function foo(). -- Manavendra Nath Manav

4 7