June 2011 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Build scatterlist covering a process' text segment?
by Arvid Brodin June 17, 2011

June 17, 2011

Hi, How do I build a scatterlist covering the text segment of a process? I have found (struct task_struct).mm->start_code and ->end_code, that gives the address (in some - unknown to me - address space) of the text segment. Since my try to convert these addresses to an sglist: sg_init_one(&sg, task->mm->start_code, <length>); failed miserably, I'm guessing these addresses need to be converted to some address space compatible with sg_init_one()/sg_set_buf() before use? (I probably need to search for pages containing these addresses?) Thanks, Arvid Brodin Enea Services Stockholm AB

5 11

Regarding virtual address space of the kernel...
by Naman shekhar Mishra June 17, 2011

June 17, 2011

I've been trying to understand this for a while with little success so any help would be hugely appreciated... Suppose I have 512 MB of physical RAM available in the system. The top 1 GB part of the 4 GB virtual address space maps *directly* starting from the 0 physical address (mapped by kernel). (Question 1) **Doesn't that mean that the physical RAM is not enough to support this mapping (I mean, only 512 MB will be directly mapped be the kernel. Moreover, no physical space will be left for user space mapping)? And even if I have 1 GB of physical RAM installed, where would all the processes get mapping from since this this 1 GB will be mapped in the address space of the kernel? ** I read in a book: "The address space after PAGE OFFSET is reserved for the kernel and this is where the complete physical memory is mapped (eg. if a system has 64mb of RAM, it is mapped from PAGE OFFSET to PAGE OFFSET + 64mb)." (Question 2, somewhat related to Q1)**Does this mean that no physical memory is left to be mapped by user space virtual memory (i.e. if all physical memory is mapped by address above PAGE_OFFSET, what is mapped by address below PAGE_OFFSET)?** (Question 3)**Also, why can't all memory, (PAGE_OFFSET to PAGE_OFFSET + 1 GB) be mapped to this 64 MB. After all pages can be swapped out and new pages can be brought in. (Question 4)**Also, when we say that kernel can map 896 MB (ZONE_NORMAL), does this 896 MB refer to virtual space or physical space?** Little (ok, very) confused so kindly explain... Thank you.

2 1

export and static?
by Gasparini Andrea June 17, 2011

June 17, 2011

Hi, is there a reason to have a symbol both static and exported through EXPORT_SYMBOL? If i'm not wrong, this way you can use it from a module, but not using in compiled files. am I right? Thanks, bye! -- - gaspa -

1 0

Linux kernel thread model
by manish honap June 17, 2011

June 17, 2011

Hi all Can someone please tell me what is the threading model of linux kernel ? user space thread:kernel thread process - n:1 or m:n or 1:1 thanks and regards - Manish

4 5

how to write a user space driver?
by 史星星 June 17, 2011

June 17, 2011

hello, i want to write a user space driver in linux,how to write?

4 3

just a test
by 史星星(研六福州) June 17, 2011

June 17, 2011

Hello, Just a test. Best regards! ------------------------------------------------- 史星星福建星网锐捷网络有限公司网研六部福州市金山大道618号橘园洲星网锐捷科技园26号楼4层 Tel : 15985751253 VOIP: 28053888-3141 -------------------------------------------------

1 0

Re:
by Althaf June 16, 2011

June 16, 2011

Please add a subject when you post, kindly read RFC 1855. - /althaf k backer/

1 0

Getting started with kernel sources [Was: No subject]
by Daniel Baluta June 16, 2011

June 16, 2011

On Thu, Jun 16, 2011 at 2:41 PM, Venkateswarlu P <p.venkatesh551(a)gmail.com> wrote: > how to understand the kernerl source files in a simple way > > > what header files i have to understand first > > > for example to understand do_fork() function for process > creation which is defined in kernel/fork.c There's no shortcuts. :) Use dump_stack() in various places and check what functions are called. Also use lxr ([1]) for code browsing. Please add a relevant Subject description to your emails. thanks, Daniel. [1] http://lxr.linux.no/

1 0

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

3 3

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 >

1 0