February 2014 - kernelnewbies@kernelnewbies.org

Re: [kernel]which the file define the variable of "phys_base"?
by Sunny Feb. 25, 2014

Feb. 25, 2014

It didn’t show me anything like that. It worked well. Here is what I have - note that I changed couple of things in printk statement but that shouldn’t affect your errors: __________________________________________________ Program - lx.c #include <linux/module.h> // for printk() #include <linux/mm.h> // for struct page #include <asm/page.h> // for struct page #include <asm/pgtable.h> // for ZERO_PAGE static int __init init_hello( void ) { int i; struct page * zero_page; printk(KERN_ALERT "\n Kello, the first! \n\n" ); i = 0x100; zero_page = ZERO_PAGE(&i); printk(KERN_ALERT " the ZERO address is %p", zero_page); return 0; } static void __exit exit_hello( void ) { printk(KERN_ALERT "\n Goodbye now... \n\n" ); } MODULE_LICENSE("GPL"); module_init(init_hello); module_exit(exit_hello); Makefile obj-m :=lx.o KDIR= /lib/modules/$(shell uname -r)/build all: $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules clean: rm -rf $(wildcard *.o *.ko mo* Mo* *.mod.c) ____________________________________________________ Running make gives me(I’m in a Virtual Machine so the page addresses may be messed up): sunny@ubuntu: make make -C /lib/modules/3.11.0-12-generic/build SUBDIRS=/home/sunny/Documents/ modules make[1]: Entering directory `/usr/src/linux-headers-3.11.0-12-generic' Building modules, stage 2. MODPOST 1 modules make[1]: Leaving directory `/usr/src/linux-headers-3.11.0-12-generic' sunny@ubuntu: sudo insmod lx.ko sunny@ubuntu: sudo rmmod lx sunny@ubuntu: sudo dmesg | tail -6 [48391.359434] Kello, the first! [48391.359434] [48320.368773] the ZERO address is ffffea0000079b40 [48391.359439] the ZERO address is ffffea0000079b40<1>[48411.409906] [48411.409906] Goodbye now... [48411.409906] Hope this helps! Don’t forget to ‘reply all’ so that others in the mailing list could also see your/my problem/solution. - Sunny On Feb 24, 2014, at 7:32 PM, lx <lxlenovostar(a)gmail.com> wrote: > hi : > If i command the "insmod zero.ko"; the wrong messages is: > ############## > insmod: error inserting 'zero.ko': -1 Unknown symbol in module > ############## > > > 2014-02-25 2:33 GMT+08:00 Sunny <sundarcs(a)gwu.edu>: > Hi, > > I’m not sure about the “pays_base” warning, but your code runs fine in my machine. What happens if you ignore the warning and load the module anyway? > > - Sunny > > On Feb 24, 2014, at 9:04 AM, lx <lxlenovostar(a)gmail.com> wrote: > >> hi all: >> the codes is: >> ######################################### >> #include <linux/module.h> // for printk() >> #include <linux/mm.h> // for struct page >> #include <asm/page.h> // for struct page >> #include <asm/pgtable.h> // for ZERO_PAGE >> >> static int __init init_hello( void ) >> { >> int i; >> struct page * zero_page; >> printk( "\n Kello, the first! \n\n" ); >> i = 0x100; >> zero_page = ZERO_PAGE(&i); >> printk(" the ZERO address is %p", zero_page); >> return 0; >> } >> >> static void __exit exit_hello( void ) >> { >> printk( "\n Goodbye now... \n\n" ); >> } >> >> MODULE_LICENSE("GPL"); >> module_init(init_hello); >> module_exit(exit_hello); >> ######################################### >> >> I complier it. by: >> ######################################### >> make -C /lib/modules/`uname -r`/build M=`pwd` >> ######################################### >> >> the results is: >> ######################################### >> [root@localhost kernel_test]# make -C /lib/modules/`uname -r`/build M=`pwd` >> make: Entering directory `/usr/src/kernels/2.6.18-308.el5-x86_64' >> CC [M] /opt/lx/kernel/kernel_test/zero.o >> Building modules, stage 2. >> MODPOST >> WARNING: "phys_base" [/opt/lx/kernel/kernel_test/zero.ko] undefined! >> LD [M] /opt/lx/kernel/kernel_test/zero.ko >> make: Leaving directory `/usr/src/kernels/2.6.18-308.el5-x86_64' >> ######################################### >> >> I try to find the file which defined the "phys_base", for examples; >> phys_base >> >> Defined as a variable in: >> arch/sparc/mm/init.c, line 40 >> arch/sparc64/kernel/sparc64_ksyms.c, line 110 >> arch/sparc64/mm/init.c, line 47 >> include/asm-sparc/page.h, line 160 >> include/asm-sparc/pgtable.h, line 122 >> include/asm-sparc64/pgtable.h, line 227 >> >> But I can't find the file of init.c in my computer. Please tell me some ways to solve it, thank you. >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > >

1 0

Need help regarding Mailing list
by Kalyan Kodamagula Feb. 25, 2014

Feb. 25, 2014

I had subscribed to the mailing list of the below : kernel code for beg's and linux sub-system /drivers. I got mails from the subscribed ML.I was wondering ppl all are asking douts or suggestion via mails and i cannot see any threads for the same mail.It was quiet confusing for me where the thread starts and ends. Is there any links like : http://forum.kernelnewbies.org/ ? if yes please point it. where we can see replies on the same thread. Please suggest me if anything wrong im doing. Thanks.

2 1

Kernel Development
by subham soni Feb. 25, 2014

Feb. 25, 2014

Hello, I am a newbie to kernel development. I would like to develop my own kernel from scratch. From where should I start from? I have a good experience of the commands in Linux (Ubuntu,Fedora,Debian,Slackware). I googled out and I came to know that I should start from Device Drivers. Now which device driver should I code? Or should I master Shell Scripting? For developing a kernel (my aim here would be to increase the battery life, since most laptops have only 1.30 hrs or 2.00 hrs in Linux OS) and 3.00 hrs in Windows Environment. How should I start and from where?

10 11

Questions about slab and mmap
by Le Tan Feb. 25, 2014

Feb. 25, 2014

Hello, I am writing a driver module and doing something with slab and mmap. Now I have some problems and need help. 1. I use kmem_cache_create() to create my own slab cache. It returns success. But I can't find my slab item in /proc/slabinfo. Why? 2.If I want the object in the slab cache to be page-aligned, what should I do? Because I want to alloc a memory of size 4096B, and want the memory to be in one page. 3. My driver module maps pages, allocating by kmem_cache_alloc(), to userspace through mmap(). In the userspace program, I first mmap() my driver device, then read something from the address returned, then munmap() it. Sometimes after the program calls munmap(), some error messages will be printed to the log: [42522.596729] BUG: Bad page map in process logger_pro pte:8000000612a30025 pmd:314175067 What will be possible reasons? Now I will explain my problems in detail. My module is called "logger". Logger maintains a list of pages (each of them is 4096B). Kernel will put some data into logger. Logger put them in the list of pages in order. When a page is full, logger will alloc another page, and then fill it with data. For efficiency, I use slab. data_cache = kmem_cache_create("logger_data", 4096, 0, 0, NULL); //I use this to create my own cache. This is called in the init function of my module kmem_cache_alloc(data_cache, GFP_ATOMIC); // I use this to alloc a new page, use GFP_ATOMIC to avoid sleep. It is called in another place Then I insmod logger. There is no error message. And my driver seems to work. However, I can't find the corresponding item in /proc/slabinfo. Why? I then write a userspace program called "logger_pro" to read data from logger into a file. For efficiency, I ues mmap() to map one page at a time, then read the data to the file.It is as follows: while(1) { str = mmap(vma); //always map the same address and offset (they are set to zero), logger will handle this fwrite(str, 4096, fd); munmap(str); } In logger module, the logger_vma_fault() function will always returns the first page in the list. When logger_pro munmap(), logger's function logger_vma_close() will be called. In logger_vma_close(), logger delete the page that has been mapped just now using kmem_cache_free(). So, though logger_pro always mmap() the same address and logger always return the fisrt page, logger_pro will eventually read all the data out of logger and logger will delete all the pages that have been read. Everything seems to be OK. But sometimes there are errors in the log: [42522.596689] logger_mmap():start:7f8ff57be000, end:7f8ff57bf000 //this is the mmap() function of my device module [42522.596694] logger_vma_fault():vmf->pgoff:0d,start:7f8ff57be000,pgoff:0,offset:0 //this is the fault function of struct vm_operations_struct [42522.596729] BUG: Bad page map in process logger_pro pte:8000000612a30025 pmd:314175067 //this is the error [42522.596740] page:ffffea00184a8c00 count:2 mapcount:-2146959356 mapping: (null) index:0xffff880612a36000 [42522.596747] page flags: 0x200000000004080(slab|head) [42522.596811] addr:00007f8ff57be000 vm_flags:04040071 anon_vma: (null) mapping:ffff880613b25f08 index:0 [42522.596824] vma->vm_ops->fault: logger_vma_fault+0x0/0x140 [logger] [42522.596834] vma->vm_file->f_op->mmap: logger_mmap+0x0/0xd50 [logger] [42522.596842] CPU: 1 PID: 21571 Comm: logger_pro Tainted: G B IO 3.11.0+ #1 [42522.596844] Hardware name: Dell Inc. PowerEdge M610/000HYJ, BIOS 2.0.13 04/06/2010 [42522.596846] 00007f8ff57be000 ffff880314199c98 ffffffff816ad166 0000000000006959 [42522.596851] ffff880314539a98 ffff880314199ce8 ffffffff8114e270 ffffea00184a8c00 [42522.596854] 0000000000000000 ffff880314199cc8 00007f8ff57be000 ffff880314199e18 [42522.596858] Call Trace: [42522.596867] [<ffffffff816ad166>] dump_stack+0x46/0x58 [42522.596872] [<ffffffff8114e270>] print_bad_pte+0x190/0x250 [42522.596877] [<ffffffff8115027b>] unmap_single_vma+0x6cb/0x7a0 [42522.596880] [<ffffffff81150bd4>] unmap_vmas+0x54/0xa0 [42522.596885] [<ffffffff81155aa7>] unmap_region+0xa7/0x110 [42522.596888] [<ffffffff81157f97>] do_munmap+0x1f7/0x3e0 [42522.596891] [<ffffffff811581ce>] vm_munmap+0x4e/0x70 [42522.596904] [<ffffffff811591bb>] SyS_munmap+0x2b/0x40 [42522.596915] [<ffffffff816bc9c2>] system_call_fastpath+0x16/0x1b [42522.596920] logger_vma_close():start:7f8ff57be000, end:7f8ff57bf000, vmas:0 //this is the close function of struct vm_operations_struct So what is wrong here? Any suggestions? Thanks! I am sorry that this email is a little messy.

2 2

Object file section efficiency
by Matt Davis Feb. 24, 2014

Feb. 24, 2014

Hello, Suppose I have some initialized data stored in the .data section of my kernel module. Now, as it turns out, that data should have been made constant, but the latter 'const' linkage qualifer was left off of the declaration of the variable. This led me to the following question: Are there any memory efficiencies with how the kernel loads the .data vs the .rodata sections into memory? Will the information stored in .rodata have better cache performance than that stored in .data? -Matt

2 1

GSoC 2014 for students, a kernel related idea
by Manu Gupta Feb. 24, 2014

Feb. 24, 2014

Hey Fellas GSoC was recently announced and we at openSUSE have one kernel related idea, I hope this will be helpful new kernel contributors. Please check http://en.opensuse.org/openSUSE:GSOC_ideas#Add_virtual_machine_snapshot_sup… http://en.opensuse.org/openSUSE:GSOC_ideas#Implement_a_test_driver_for_the_… All your queries can be answered at opensuse-project at opensuse.org related to openSUSE and gsoc -- Regards Manu Gupta

1 0

[kernel]which the file define the variable of "phys_base"?
by lx Feb. 24, 2014

Feb. 24, 2014

hi all: the codes is: ######################################### #include <linux/module.h> // for printk() #include <linux/mm.h> // for struct page #include <asm/page.h> // for struct page #include <asm/pgtable.h> // for ZERO_PAGE static int __init init_hello( void ) { int i; struct page * zero_page; printk( "\n Kello, the first! \n\n" ); i = 0x100; zero_page = ZERO_PAGE(&i); printk(" the ZERO address is %p", zero_page); return 0; } static void __exit exit_hello( void ) { printk( "\n Goodbye now... \n\n" ); } MODULE_LICENSE("GPL"); module_init(init_hello); module_exit(exit_hello); ######################################### I complier it. by: ######################################### make -C /lib/modules/`uname -r`/build M=`pwd` ######################################### the results is: ######################################### [root@localhost kernel_test]# make -C /lib/modules/`uname -r`/build M=`pwd` make: Entering directory `/usr/src/kernels/2.6.18-308.el5-x86_64' CC [M] /opt/lx/kernel/kernel_test/zero.o Building modules, stage 2. MODPOST *WARNING: "phys_base" [/opt/lx/kernel/kernel_test/zero.ko] undefined!* LD [M] /opt/lx/kernel/kernel_test/zero.ko make: Leaving directory `/usr/src/kernels/2.6.18-308.el5-x86_64' ######################################### I try to find the file which defined the "phys_base", for examples; phys_baseDefined as a variable in: - arch/sparc/mm/init.c, line 40<http://lxr.oss.org.cn/source/arch/sparc/mm/init.c?v=2.6.8#L40> - arch/sparc64/kernel/sparc64_ksyms.c, line 110<http://lxr.oss.org.cn/source/arch/sparc64/kernel/sparc64_ksyms.c?v=2.6.8#L1…> - arch/sparc64/mm/init.c, line 47<http://lxr.oss.org.cn/source/arch/sparc64/mm/init.c?v=2.6.8#L47> - include/asm-sparc/page.h, line 160<http://lxr.oss.org.cn/source/include/asm-sparc/page.h?v=2.6.8#L160> - include/asm-sparc/pgtable.h, line 122<http://lxr.oss.org.cn/source/include/asm-sparc/pgtable.h?v=2.6.8#L122> - include/asm-sparc64/pgtable.h, line 227<http://lxr.oss.org.cn/source/include/asm-sparc64/pgtable.h?v=2.6.8#L227> But I can't find the file of init.c in my computer. Please tell me some ways to solve it, thank you.

2 1

Re: [Help] How to Replace File Operations in File System?
by freeman Feb. 24, 2014

Feb. 24, 2014

Hi Rishi, With pleasure! You can check it on https://github.com/freemandealer/droidcry on your convenience. 2014-02-19 23:17, Rishi Agrawal : > Good that you solved it your self, still if you can send me the idea > on which you are working - I may also learn something. > > > On Tue, Feb 18, 2014 at 10:04 AM, freeman <freeman.zhang1992(a)gmail.com > <mailto:freeman.zhang1992@gmail.com>> wrote: > > > > Hi > > > > The operations will not change back until your object gets > destroyed, > > whatever be the type of the object. > > > > Caching will not cause any issue here. > > > > Maybe if you can send the code we can have a look at it. > > > > > > -- > > Regards, > > Rishi Agrawal > Hi Rishi, > > It's very nice of you willing to help check my code! > I'm now very excited － problem solved! > > I spent half a day beautifying my code yesterday (so that it won't > annoy > you > that much), and find there is a problem: > > Every time there is a read/write system call, I saved the lower > file ops > and > address space ops. In their replacement(upper operations), I invoked > lower ones. > There's a possibility that it might saved the upper operations as > lower > ones if I > open them twice in a short time. At this point, upper operation invoke > itself! > So I check the operations before truly save and replace them and, > it works! > > Thanks to you and all the amazing people in this amazing list that > helped me, > now I get both wrapfs and my own non-filesystem module functional > for my > future work on transparent encryption, and most importantly, I've > learned and > enjoyed a lot! > > Regards > Freeman Zhang > > > > > -- > Regards, > Rishi Agrawal Regards Freeman Zhang

5 7

The purpose of calling init_waitqueue_head()
by m silverstri Feb. 22, 2014

Feb. 22, 2014

Hi, I am trying to understanding a linux driver code here: https://android.googlesource.com/kernel/exynos/+/a6a1de6334417e0800440cdf97… In here https://android.googlesource.com/kernel/exynos/+/a6a1de6334417e0800440cdf97…, it calls 'init_waitqueue_head() where wq is a "wait_queue_head_t wq;" mutex_init(&ctrl->lock); init_waitqueue_head(&ctrl->wq); But I search the whole directory for wq usage, I don't find anywhere wq is used. Can you please tell me what is the purpose of calling "init_waitqueue_head"? Thank you.

1 0

The Eudyptula Challenge
by Little Penguin Feb. 22, 2014

Feb. 22, 2014

For those wanting some Linux kernel programming exercises, try: http://eudyptula-challenge.org/

1 0