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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

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[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.

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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

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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.

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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/

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how to validate code changes in /linux/kernel directory ?
by Avinash Kumar Feb. 21, 2014

Feb. 21, 2014

Hello, I made some changes in file module.c inside /linux/kernel/ directory . How do i validate if the code compiles fine before i submit a patch? For changes under linux/drivers/ i normally use something like - make M=drivers/staging/dgnc. Is there any similar way validate changes under /linux/kernel/ directory or do i need to compile the kernel ? Thanks, Avinash

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Interrupts : request_percpu_irq function
by priyaranjan Feb. 21, 2014

Feb. 21, 2014

I was reading about request_irq() function. We have another variant of this function known as request_percpu_irq(). Can any one explain me the usage of this function? and how it is different that the traditional request_irq(). I also couldn't find a single driver using this function though this has been extensively used in architecture specific files especially the timers and the watchdog. Also it would be great, if someone can point out any document/link where I can find the description. I failed to find it from Linux kernel documentation. Regards, Priyaranjan

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Side effects of open system call
by Rahul Bedarkar Feb. 21, 2014

Feb. 21, 2014

Hi, In ioctl man page, mentioned that "Often the open(2) call has unwanted side effects, that can be avoided under Linux by giving it the O_NONBLOCK flag." I have seen open man page but can't find what are side effects of open. Does anybody know what are side effects of open in general ? Thanks, Rahul

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Sending rate decrease in TCP bidirectional test
by Varun Sharma Feb. 20, 2014

Feb. 20, 2014

Hi, I am using iperf v 2.0.5 for testing 10G card. Its a dual port card. Two 16 core machines with 64GB RAM are connected back to back. In *TCP Bidirectional test* case sending throughput decrease as compare to *TCP Unidirectional test* case sending . All cases use default setting . No extra parameter is set. In case of 4 Client threads Output comes :-- Unidirectional Send Process --- *9.6* Gbps Bidirectional Send Process ---- *4.9* Gbps In case of 8 Client threads Output comes :-- Unidirectional Send Process --- *9.7* Gbps Bidirectional Send Process -- *6.4* Gbps In case of 16 Client threads Output comes :-- Unidirectional Send Process ---* 9.7* Gbps Bidirectional Send Process -- *8* Gbps Is this problem regarding TCP/IP stack or nic card ? Regards varun

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Re: Unable to generate vmcore file.
by palik imre Feb. 20, 2014

Feb. 20, 2014

> From: Rishi Agrawal <rishi.b.agrawal(a)gmail.com> > I have been trying to debug a kernel crash in my module and need the vmcore > file for it. ... > Its a virtual machine so I do not get a lot of info on console. What kind of virtual machine? Some of them don't support kdump. Imre

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