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kernel module spanning multiple files
by amit mehta June 16, 2011

June 16, 2011

Hi, After looking at some Makefiles under Linux Driver sources which uses multiple files to create the target, i tried to write a simple hello world kernel module spanning multiple files for learning purpose. But I'm observing a strange behavior. After inserting the module, I don't see the prints getting logged into the syslog(/var/log/message) or in the dmesg. Maybe its just a C programming mistake, or is due to an incorrect Makefile but as of now I'm clueless. Here are the code snippet from the four files(hello_multi.c, helper.c, myhdr.h, Makefile) [root@localhost #] cat hello_multi.c #include <linux/kernel.h> #include <linux/module.h> #include <linux/init.h> #include "myhdr.h" static int __init hello_init(void) { printk(KERN_WARNING "Hello world\n"); foo(); //defined in anther file return 0; } static void __exit hello_exit(void) { printk(KERN_WARNING "goodbye world\n"); } module_init(hello_init); module_exit(hello_exit); MODULE_LICENSE("GPL v2"); [root@localhost #] cat helper.c #include <linux/kernel.h> #include "myhdr.h" void foo(void) { printk(KERN_WARNING "inside foo\n"); } [root@localhost #] cat myhdr.h #ifndef __MY_HDR_H #define __MY_HDR_H void foo(void); #endif [root@localhost #] cat Makefile obj-m += hello_multi.o hello_multi-objs := helper.o KERNELDIR=/lib/modules/$(shell uname -r)/build PWD=$(shell pwd) modules: make -C $(KERNELDIR) M=$(PWD) modules modules_install: make -C $(KERNELDIR) M=$(PWD) modules_install clean: rm -rf *.o *.ko *~ core .depend .tmp_versions .*.cmd *.mod.c .PHONY: modules modules_install clean Invoking 'make modules' completes with success and i am able to insert this module. [root@localhost #] make modules make -C /lib/modules/2.6.31-23-generic/build M=/home/superman/programming/ldd/hello_multi modules make[1]: Entering directory `/usr/src/linux-headers-2.6.31-23-generic' CC [M] /home/superman/programming/ldd/hello_multi/helper.o LD [M] /home/superman/programming/ldd/hello_multi/hello_multi.o Building modules, stage 2. MODPOST 1 modules CC /home/superman/programming/ldd/hello_multi/hello_multi.mod.o LD [M] /home/superman/programming/ldd/hello_multi/hello_multi.ko make[1]: Leaving directory `/usr/src/linux-headers-2.6.31-23-generic' [root@localhost #] dmesg -c [root@localhost #] insmod hello_multi.ko [root@localhost #] dmesg|tail <-- -- No messages here [root@localhost #] cat /proc/modules |grep -i hello hello_multi 727 0 - Live 0xffffffffa020b000 (PN [root@localhost #] nm hello_multi.ko 0000000000000000 r ____versions 0000000000000000 r __mod_srcversion26 0000000000000040 r __mod_vermagic5 0000000000000023 r __module_depends 0000000000000000 D __this_module 0000000000000000 T foo U printk Regards, amit

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Re: kernel module spanning multiple files
by amit mehta June 15, 2011

June 15, 2011

Whereas for a simple single file hello world kernel module, i see that the symbols in the object (hello_world.ko) for the init and exit routines. <snip> [root@localhost #] nm hello_world.ko 0000000000000000 r ____versions 000000000000000c r __mod_license17 0000000000000020 r __mod_srcversion30 0000000000000060 r __mod_vermagic5 0000000000000000 r __mod_version18 0000000000000043 r __module_depends 0000000000000000 D __this_module 0000000000000000 T cleanup_module 0000000000000000 t hello_exit < --- -------- 0000000000000000 t hello_init < -- --------- 0000000000000000 T init_module U printk <snip> Regards, amit On Wed, Jun 15, 2011 at 3:29 PM, amit mehta <gmate.amit(a)gmail.com> wrote: > Hi, > > After looking at some Makefiles under Linux Driver sources > which uses multiple files to create the target, i tried to write > a simple hello world kernel module spanning multiple files for learning purpose. > But I'm observing a strange behavior. After inserting the module, > I don't see the prints getting logged into the syslog(/var/log/message) > or in the dmesg. Maybe its just a C programming mistake, or is due to > an incorrect Makefile but as of now I'm clueless. > > Here are the code snippet from the four files(hello_multi.c, helper.c, > myhdr.h, Makefile) > > [root@localhost #] cat hello_multi.c > #include <linux/kernel.h> > #include <linux/module.h> > #include <linux/init.h> > #include "myhdr.h" > static int __init hello_init(void) > { > printk(KERN_WARNING "Hello world\n"); > foo(); //defined in anther file > return 0; > } > > static void __exit hello_exit(void) > { > printk(KERN_WARNING "goodbye world\n"); > } > > module_init(hello_init); > module_exit(hello_exit); > > MODULE_LICENSE("GPL v2"); > > [root@localhost #] cat helper.c > #include <linux/kernel.h> > #include "myhdr.h" > void foo(void) > { > printk(KERN_WARNING "inside foo\n"); > } > > [root@localhost #] cat myhdr.h > #ifndef __MY_HDR_H > #define __MY_HDR_H > void foo(void); > #endif > > [root@localhost #] cat Makefile > obj-m += hello_multi.o > hello_multi-objs := helper.o > KERNELDIR=/lib/modules/$(shell uname -r)/build > PWD=$(shell pwd) > > modules: > make -C $(KERNELDIR) M=$(PWD) modules > > modules_install: > make -C $(KERNELDIR) M=$(PWD) modules_install > > clean: > rm -rf *.o *.ko *~ core .depend .tmp_versions .*.cmd *.mod.c > .PHONY: modules modules_install clean > > Invoking 'make modules' completes with success and i am able to > insert this module. > > [root@localhost #] make modules > make -C /lib/modules/2.6.31-23-generic/build > M=/home/superman/programming/ldd/hello_multi modules > make[1]: Entering directory `/usr/src/linux-headers-2.6.31-23-generic' > CC [M] /home/superman/programming/ldd/hello_multi/helper.o > LD [M] /home/superman/programming/ldd/hello_multi/hello_multi.o > Building modules, stage 2. > MODPOST 1 modules > CC /home/superman/programming/ldd/hello_multi/hello_multi.mod.o > LD [M] /home/superman/programming/ldd/hello_multi/hello_multi.ko > make[1]: Leaving directory `/usr/src/linux-headers-2.6.31-23-generic' > [root@localhost #] dmesg -c > [root@localhost #] insmod hello_multi.ko > [root@localhost #] dmesg|tail <-- -- No messages here > > [root@localhost #] cat /proc/modules |grep -i hello > hello_multi 727 0 - Live 0xffffffffa020b000 (PN > > [root@localhost #] nm hello_multi.ko > 0000000000000000 r ____versions > 0000000000000000 r __mod_srcversion26 > 0000000000000040 r __mod_vermagic5 > 0000000000000023 r __module_depends > 0000000000000000 D __this_module > 0000000000000000 T foo > U printk > > Regards, > amit >

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Procedure Linux follows for shutting down an x86 system when ACPI is not used
by limp June 15, 2011

June 15, 2011

Hi all, I am trying to figure out the procedure that Linux follows for shutting down an x86 based system when ACPI is not used. From what I've found, when we try to shutdown the system from user-space, _reboot() system call is called with "LINUX_REBOOT_CMD_POWER_OFF" as argument. By tracking down the steps performed in the kernel when the aforementioned system call is involved, I ended up in kernel_power_off(), unlock_kernel(), and finaly do_exit() functions. The kernel_power_off() ultimately calls the native_machine_shutdown() form which Linux disables LAPIC, I/O APIC, HPET, etc. Then, after calling the unlock_kernel(), the do_exit() is called for ultimately shutting down the system. In the end of this function, I can see that the processor enters an infinite loop from which it repeatedly executes NOP instructions. That is actually the behaviour that I experience when I am not using ACPI; the system is not actually turning off but it goes into an idle state. Is this how Linux should act when ACPI is not used? I would expect in this case Linux to invoke an SMI so that the appropriate SMI function actually shutdown the system but I can't see where (and if) that takes place. Any help will be greatly appreciated. John K.

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(no subject)
by Venkateswarlu P June 14, 2011

June 14, 2011

anyone can send implementation of *fork()* library call in the library i want to know how it is get connected to the system call. ** P VENKATESWARLU M.Tech (CSE) II year NIT Calicut ,Kerala* ** *+91-9995115752

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Power saving in Multi core.
by naveen yadav June 14, 2011

June 14, 2011

Dear All, We are using ARM cortex a9. In below scenario, I want help. Multi-Core Power Saving Hot plug feature allows for making a processor offline and let the system run as if there is only a single core. Now,comes the scenario - Let there are '2' cores in the system both running at a load of 40% (i.e. total load 80%), now in this case ideally '1' CPU is sufficient. So, if we make 2nd Core offline that will make the system execute everything on core '1'. But will there be any power saving if we make any core offline under scenarios like this? Or will this have extra overhead? What are the pros and cons of working like this on Multi-Core? Regards Naveen

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IPV6 header creation for dhcpv6 packet
by Prabhu June 14, 2011

June 14, 2011

HI all, I am writing simple dhcpv6 client. I gone through the rfc of dhcp and ipv6 and understand basic. With the understanding i started to implement SOLICIT request option. I have created a packet with the below structure. struct udp_dhcp6_packet { struct ip6_hdr ip; struct udphdr udp; struct dhcp6_Message data; } PACKED; In the above structure i am able to assign the value for udp and data(i.e struct udphdr, struct dhcp6_Message). But i could not able to set the value for ip. Below is the structure of ip6_hdr. struct ip6_hdr { union { struct ip6_hdrctl { uint32_t ip6_un1_flow; /* 4 bits version, 8 bits TC, 20 bits flow-ID */ uint16_t ip6_un1_plen; /* payload length */ uint8_t ip6_un1_nxt; /* next header */ uint8_t ip6_un1_hlim; /* hop limit */ } ip6_un1; uint8_t ip6_un2_vfc; /* 4 bits version, top 4 bits tclass */ } ip6_ctlun; struct in6_addr ip6_src; /* source address */ struct in6_addr ip6_dst; /* destination address */ }; I want to set the ip6_dst value as ff02::1:2 and the ip6_src address as fe80::220:4aff:fea8:8e4a and remaining options. But i dont have any idea how to set these values. I googled many times and not able to get the idea to creat ipv6 header. Kindly help me to solve my problem? Note : I don't know whether this is right place to ask this question . If i am wrong , i am sorry. Thanks in advance , Prabhu

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struct task_struct
by Venkateswarlu P June 14, 2011

June 14, 2011

Now ,iam reading *Linux kernel Development * *3rd ed * I want the explanation of each member of *struct task_struct *found in <linux/sched.h> ** P VENKATESWARLU M.Tech (CSE) II year NIT Calicut ,Kerala* ** *+91-9995115752

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if stmt in kernel source
by Venkateswarlu P June 14, 2011

June 14, 2011

explain about * likely * and * unlikely * constructs used in*if * stmt ** P VENKATESWARLU M.Tech (CSE) II year NIT Calicut ,Kerala* ** *+91-9995115752

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What does the ENTRY() macro do?
by Naman shekhar Mishra June 13, 2011

June 13, 2011

I have seen this macro at a lot of places. e.g. ENTRY(system_call).Can anyone tell me where is it defined and what does it do? (kernel version 2.6.39).

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Error compiling a fresh kernel
by SADA SIVA REDDY S June 13, 2011

June 13, 2011

Hi All, I wanted to start my hands on on Linux kernel and got stuck at the beginning with build failure. ( I have tried this few months back when it worked fine but failing after upgrade.) with following error: Root device is (8, 6) Setup is 14108 bytes (padded to 14336 bytes). System is 4423 kB CRC 4e90e12c Kernel: arch/x86/boot/bzImage is ready (#1) Building modules, stage 2. MODPOST 3274 modules ERROR: "pm_idle" [arch/x86/kernel/apm.ko] undefined! ERROR: "default_idle" [arch/x86/kernel/apm.ko] undefined! WARNING: modpost: Found 30 section mismatch(es). To see full details build your kernel with: 'make CONFIG_DEBUG_SECTION_MISMATCH=y' make[1]: *** [__modpost] Error 1 make: *** [modules] Error 2 ssreddy@N5030:~/linux-2.6$ I am looking to dedicate few hours every week from now. I am refraining from attaching the .config file to wider list. I can send in unicast if some one is willing to help me fix if there are problems in .config. I have copied the old config file from installed ubuntu 11.04 yes ' ' | make oldconfig -- to generate my basic config file. Thanks, SADA

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