September 2013 - kernelnewbies@kernelnewbies.org

Formatting timestamps in the kernel
by Neil Baylis Sept. 18, 2013

Sept. 18, 2013

My driver creates an entry in /proc that displays time related events. Is there a way to format timestamps, as absolute date & time, honoring timezones etc., within the kernel? I think I read somewhere that timezones are considered a userspace concept, and as such are not supported within the kernel. Thanks, Neil

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/proc/net/dev no such file or dir
by Hatte John Sept. 17, 2013

Sept. 17, 2013

hi: I am trying to boot up my linux kerel from virtual machine ,everything goes fine . but when I typed 'ifconfig' command , it reports no such file : /proc/net/dev . What is the reason ? I have enable netcard for my virtual machine ,is this a problem of software or hardware? Is the file " /proc/net/dev" created at netcard initailize function ? Thanks!

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Significance of " /proc/<pid>/root"
by Arun M Kumar Sept. 17, 2013

Sept. 17, 2013

What is the significance of the directory named root inside /proc/<pid> ? ex: ---------------------------------------------------------------------------------- arunkumar@arun-ThinkPad-Edge-E530:/proc/2543/root$ ls bin cdrom etc initrd.img lib media opt root sbin srv tmp var vmlinuz.old boot dev home initrd.img.old lost+found mnt proc run selinux sys usr vmlinuz ----------------------------------------------------------------------------------

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Failing to install linux 3.10.10 on Intel xeon E5-2665
by Rakhi Hemani Sept. 16, 2013

Sept. 16, 2013

Dear all, I am trying to install linux 3.10.10 using Arch Linux on a xeon machine with following configuration. cpu family : 6 model : 45 model name : Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz It gives a error at boot time APEI Generic Hardware error source: 32993. For booting x86_64 kernel there is no such error for i386. Please advice, actually I need to access the uncore performance counters that are available only using latest linux kernel. Thanks -- Rakhi Hemani Phd Scholar Roll Number PhD1207

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Re: i just opened up my online intro kernel programming, course for free ( Arun M Kumar)
by Arun M Kumar Sept. 15, 2013

Sept. 15, 2013

Great.... Finally !!!! :) \m/

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Fwd: Understanding disassembly x86 + understanding function call + parameter pass and stack frame
by nidhi mittal hada Sept. 15, 2013

Sept. 15, 2013

---------- Forwarded message ---------- From: nidhi mittal hada <nidhimittal19(a)gmail.com> Date: Tue, Aug 6, 2013 at 2:16 PM Subject: Understanding disassembly x86 + understanding function call + parameter pass and stack frame To: Kernelnewbies <kernelnewbies(a)nl.linux.org> Cc: Mulyadi Santosa <mulyadi.santosa(a)gmail.com> Hi All, I am using crash tool to analyze core dump obtained from red hat linux on x86_64 platform. And crash tool gives a stack trace of panic. But its does not show function parameters which were passed in this stack trace. So i have to disassemble and understand the value of parameters passed to these functions, while it panicked. Which i am not able to understand much. I would request help in knowing, how to understand disassembled function call , on x86_64 arch. Putting some of the doubts.. a)like which sequence the parameters, return address, etc are pushed on stack? b)Which registers are used, if some registers play some spl. role ? c)lets say for a program a.c i use gcc -S a.c ...do we have some other command to generate somewhat more clear assembly code, may be with some comments in english Any kind of help in understanding this will be appreciated .. Thanks Nidhi -- Thanks & Regards Nidhi Mittal Hada http://nidhi-searchingmyself.blogspot.com/

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by GMAIL Sept. 15, 2013

Sept. 15, 2013

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i just opened up my online intro kernel programming course for free
by Robert P. J. Day Sept. 15, 2013

Sept. 15, 2013

given that i just haven't had the time to keep working on it (and i'm going to republish it anyway, somehow, for free), i've dropped the payment requirement of the intro to kernel programming course i wrote back here: http://www.crashcourse.ca/ up in the top left, you can see two links to courses -- the original and the 2nd edition. the original is now completely free, have at it. the 2nd edition (also free) is simply the somewhat-updated version of the free part of the first edition, so you can (i think) start with the 2nd edition and, when it runs out, go back to the 1st edition and pick up where that left off. yes, what's there could stand some updating but it's still probably adequate to get you going, and writing and loading your first kernel module and character driver. my plan for the future is for a totally-updated similar course, again designed for newbies. not sure how i want to make it available -- perhaps through github or some other social platform -- but whenever or wherever it appears, it will be free. more on all of this in a bit. questions? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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Plug/unplug events of headphone
by Dmitry Kolesov Sept. 14, 2013

Sept. 14, 2013

Hello. I want to catch plug/unplug events of headphone. Could anybody explain where I need to search? Regards, Dmitry

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Regarding wrong usage of spin_lock_bh
by Mohammed Shafi Sept. 14, 2013

Sept. 14, 2013

Hi, I see a warning, /qsdk/qca/src/linux/kernel/softirq.c:159 local_bh_enable_ip+0x5c/0xe0() spin_lock_bh. While dev_ioctl is called from user context, not sure why we have the warning because of the following reasons in softirq.c : 159 1. in_irqs - interrupt handler context (So we need to use spin_lock_irq_save ) 2. disabled_irqs - interrupts are disabled (spin_lock should be good enough ). Can some one give me more thoughts, I can see that its not necessary to call spin_lock_bh from softirq context, what are the other scenarios where this might be a problem or not necessary ? The above warning comes from dev_ioctl (user context), when a new network interface is added. thanks, shafi

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