February 2013 - kernelnewbies@kernelnewbies.org

scripts/basic/fixdep issue
by Sync Rico Feb. 22, 2013

Feb. 22, 2013

Hi, I have a problem with fixdep: a kernel was compiled on a PC and when trying to build a kernel module for that kernel I use a different PC tha has a different glibc version than the one used to compile fixdep. In order to fix the problem I'm thinking that maybe to build fixdep with "--static" but my knowledge about linux kernel is not that great and I would like some input please. Also, is there any chance to just rebuild fixdep without rebuilding the whole kernel? Is there any other possibility other then the --static one? Kernel used is 2.6 Thanks, syncbq

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Queries on USB skeleton Driver
by sanchayan maity Feb. 22, 2013

Feb. 22, 2013

Hello, I wanted to use the usb-skeleton driver for transferring data to a pen drive. I am using Ubuntu 12.04 with kernel version 3.2.0. I remove the usb-storage driver with rmmod and then inserted the skeleton module. The module is inserted successfully. On inserting the drive, usb-storage module gets automatically loaded. To avoid this, i tried blacklisting the module by including a blacklist entry in blacklist.conf and rebooting. This didn't work either and usb-storage gets automatically loaded again. Can someone point out how i can use the usb-skeleton driver and also test it. I also have Arch linux set up, but, i have not tried the above on it yet. Thanks & Regards, Sanchayan.

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Why would some process swap in place of reclaiming free(cached) memory
by Soham Chakraborty Feb. 22, 2013

Feb. 22, 2013

Hi all, I posted this question in linux-mm list as well but it didn't spawn much interest. So, I am putting the same question here also. Would love if someone can put some traction. The question is salivating and simple. When we have free and lotsa cached memory in a system (irrespective of distro and kernel), why would some process end up in swap space, I understand the overcommit mode of vm, the default value of 0 and what it does. I also know that the cache might be dirty and we don't might not want to allocate free pages thinking that we might go under the watermark of low. But, I mainly end up getting this question from end users - why would things swap if I have free memory. I guess, technically we can't stop swapping even if we set vm.swappiness to 0 but well, I think I have said what I need to said. If you need data, I can provide those. Any reference to source where it gives the condition to transfer some pages to swap, despite of having free memory, would be highly appreciated. I tried to find in mm/vmscan.c but didn't get much success. Soham

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unsubscibe
by Sandeep Sonawane Feb. 21, 2013

Feb. 21, 2013

Hi, Please remove my email id sandeep.sonawane(a)gmail.com from this DL. Regards, Sandeep

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cpu_relax(), rep: nop, and PAUSE
by David Shwatrz Feb. 20, 2013

Feb. 20, 2013

Hi, kernel newbies, We have: #define cpu_relax() asm volatile("rep; nop") in arch/x86/boot/boot.h. Why don't we use the PAUSE assembler instruction here ? According to Intel manuals, Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 2B: "This instruction was introduced in the Pentium 4 processors, but is backward compatible with all IA-32 processors. In earlier IA-32 processors, the PAUSE instruction operates like a NOP instruction. The Pentium 4 and Intel Xeon processors implement the PAUSE instruction as a delay. The delay is finite and can be zero for some processors. This instruction does not change the architectural state of the processor (that is, it performs essentially a delaying no-op operation). This instruction’s operation is the same in non-64-bit modes and 64-bit mode." And AFAIK, in spinlocks , PAUSE indeed replaced the rep;nop. Any ideas? Best, DS

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Re: test jiffies on ARM SMP board
by anish kumar Feb. 20, 2013

Feb. 20, 2013

On Wed, 2013-02-20 at 17:30 +0000, Russell King - ARM Linux wrote: > On Wed, Feb 20, 2013 at 10:54:41PM +0530, anish kumar wrote: > > On Thu, 2013-02-21 at 00:39 +0800, buyitian wrote: > > > i am confused about my test. in one device driver, > > > i put below code: > > > > > > printk("start to test test jiffies\n"); > > > > > > local_irq_save(flags); > > > > > > jf1 = jiffies; // read jiffies first time > > > > > > // hold cpu for about 2 seconds(do some calculation) > > > > > > jf2 = jiffies; // read jiffies after 2 seconds > > > > > > local_irq_restore(flags); > > > > > > printk("jf1:%lu, jf2:%lu\n", jf1, jf2); > > > > > > and the output is as below: > > > > > > <4>[ 108.551124]start to test test jiffies > > > <4>[ 110.367604]jf1:4294948151, jf2:4294948151 > > > > > > the jf1 and jf2 are the same value, although they are > > > read between 2 seconds interval, i think this is because > > > i disabled local interrupt. > > > but the printk timestamp is from 108.551124 to 110.367604, > > > which is about 2 seconds. and on my platform, printk timestamp > > > is got from the function read_sched_clock: > > > static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read; > > > > > > and function jiffy_sched_clock_read() is to read from jiffies. > > > > > > it seems that the jiffies is frozen when local irq is disabled, > > > but after local_irq_restore(), the jiffies not only start > > > to run, but also recover the lost 2 seconds. > > > > > > is the jiffies updated from another cpu when irq is disabled on > > > local cpu? > > > > > > is there some internel processor interrupt between cpu1 and cpu0 > > > after local irq is re-enabled so that jiffies recover the lost 2 seconds? > > I think it is because of the fact that some RTC registers keep the > > The RTC has nothing to do with this. > > As soon as the IRQs are allowed again (immediately after the > local_irq_restore()) the pending interrupt - including the timer > interrupt will be processed. > > At this point, because we read the clocksource, we can see that two > seconds have passed, and so we advance jiffies by the elapsed time. So I understand there is some register which stores the elapsed time and in my understanding it was RTC register which is wrong as suggested by you.I suppose some timer register is used for this information on the SOC. > > This means printk() sees that the two seconds have passed. But because > you're reading from jiffies within the interrupt disabled region, that > code can't see the missed ticks.

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.a library support for android
by Shivaprasad Imdapur Feb. 20, 2013

Feb. 20, 2013

Hi All, I got some library file to support Biometric sensor device for android. The library is libfpc4030.a My Doubts are, 1. What is *.a" file? 2. Is libfpc4030.a is an driver support library ?. If so where exactly keep this in android source code and compile? 2. These library file will communicate directly to hardware or we need to write any driver support code ? Thanks

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Re: gdtr value
by Anuz Pratap Singh Tomar Feb. 20, 2013

Feb. 20, 2013

On Tue, Feb 19, 2013 at 10:18 PM, horseriver <horserivers(a)gmail.com> wrote: > On Mon, Feb 18, 2013 at 12:25:43PM +0000, Anuz Pratap Singh Tomar wrote: > > On Mon, Feb 18, 2013 at 1:55 AM, horseriver <horserivers(a)gmail.com> > wrote: > > > > > Intel® 64 and IA-32 Architectures > > Software Developer’s Manual > > Volume 3A: > > System Programming Guide, Part 1 > > page 65 > > > > The linear address of the base of the GDT is contained in the GDT > register > > (GDTR); > > the linear address of the LDT is contained in the LDT register (LDTR). > > > > Thanks! > > As the value is a linear address , so when load an segment descriptor > from an address , > such as lss ubstruction: lss 0x10023,%esp , cpu will check to make sure > this stack descriptor > exist in gdt . > So , we will get a linear address by the gdtr value and the > descriptor's index , then *if this linear address* > has not phisical page mapped , it will cause a pagefault trap.then ,how > to resolve this trap? > > > Please use reply all or add kernelnewbies to CC I am not very sure of how this trap will be resolved, but you can have a look at this: Understanding Linux Kernel Section 9.4 http://www.makelinux.net/books/ulk3/understandlk-CHP-9-SECT-4 > > > > > However for 32 bit registers, this document provides some details in > > protected mode: > > > > http://home.swipnet.se/smaffy/asm/info/PMODEDetailedApproach.txt > > > > > > > > > thanks! > > > > > > _______________________________________________ > > > Kernelnewbies mailing list > > > Kernelnewbies(a)kernelnewbies.org > > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > > > > > > > > > -- > > Thank you > > Warm Regards > > Anuz > -- Thank you Warm Regards Anuz

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SIGKILL and a sleeping kernel module
by Kevin Wilson Feb. 20, 2013

Feb. 20, 2013

Hi all, I am trying to send a SIGKILL to a kernel module which is sleeping. I added a printk after the sleep command. Sending a SIGLKILL (by kill -9 SIGLKILL pidOfKernelThread) does **not** yield the message from printk("calling do_exit\n"); which is immediately after the msleep() command, as I expected. Moreover, ps before and after the kill show 'D' in the STAT column (STATUS), which means that the process is sleeping (If I am not wrong). Any ideas why ? below is the code: #include<linux/init.h> #include<linux/module.h> #include<linux/kernel.h> #include<linux/kthread.h> #include<linux/sched.h> #include <linux/delay.h> struct task_struct *task; int thread_function(void *data) { int exit_sig = SIGKILL; allow_signal(SIGKILL); printk("in %s\n",__func__); // sleep for a second msleep(60000); printk("calling do_exit\n"); do_exit(exit_sig); return 0; } static int kernel_init(void) { task = kthread_create(thread_function,NULL,"MY_KERNEL_THREAD"); return 0; } static void kernel_exit(void) { printk("in kernel_exit\n"); kthread_stop(task); } module_init(kernel_init); module_exit(kernel_exit); MODULE_AUTHOR("Tester"); MODULE_DESCRIPTION("test"); MODULE_LICENSE("GPL"); rgs, Kevin

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Re: Suppress all boot output (framebuffer?) - embedded linux distro
by Ivan Nikolaev Feb. 19, 2013

Feb. 19, 2013

-------- Original Message -------- Subject: Re: Suppress all boot output (framebuffer?) - embedded linux distro Date: Tue, 19 Feb 2013 22:52:25 +0100 From: Ivan Nikolaev <voidexp(a)gmail.com> To: Mulyadi Santosa <mulyadi.santosa(a)gmail.com> On Tue 19 Feb 2013 08:00:52 PM CET, Mulyadi Santosa wrote: > On Tue, Feb 19, 2013 at 8:50 PM, Ivan Nikolaev <voidexp(a)gmail.com> wrote: >> I'm developing an ubuntu 12.04 (LTS) based embedded distribution, which >> basically is a normal ubuntu stripped down to bare minimal packages, >> which runs a minimal XOrg server with one single full-screen >> application. What I want is to suppress every single char of console >> output since the bootloader passed control to the kernel, and possibly >> show instead of that some static text and/or image. What I thought is to >> try to disable printk-s and to write some kind of patch which uses the >> framebuffer to show the logo. Is that possible/difficult? Can you >> eventually explain where I should dig? > > > IIRC, isn't that what ubuntu 12.04 does during boot stage by default ? > i mean, no boot message shown.... > > Yes, I guess Ubuntu version of GRUB is slightly modified, and it uses Plymouth to provide that "nice" (and buggy on some machines) graphic bootsplash. What I need is to avoid virtual consoles at all, also, I need one static image visualized by framebuffer, which then smoothly passes to my GUI app. Even more, being my app Qt based, I think about throwing away the Xorg server and use Qt's support for framebuffer. So, it will probably do a nice job. Hope I've explained what I need. For example, on Android devices how this thing is done? You turn on the device, and then the loading animation is displayed for a while. Everything goes smooth, no glitches, and I suppose, there's no Plymouth :)

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