May 2017 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Re: I want write more important things
by Roman Storozhenko May 18, 2017

May 18, 2017

> Hello, > I am interested in wrinting code in Linux kernel and I started write kernel modules. I have some basics about kernel development- I red Robert's Love book. My the biggest project with kernel code is simple module, which create char device which can execute commands as root. Actually I'm reading Linux device drivers 3rd edition. And I haven't any idea what I could doing. I have many ebooks about kernel, but I prefer learn by writing some code. Sorry for my banal question (propably you haven't many time), but when someone answer me, I will be very very thankful. I would suggest you to: 1) Complete eudyptula challenge. It contains 20 kernel-related tasks. I have completed 8th task and awaiting to response and I want to say that this is a very good challenge for newbies. 2) Pick one of the areas in which you want to participate in. It might be virtualization, networking, storage, drivers, etc.. Any of that. Go to the appropriate kernel bug tracker, pick a bug and then try to reproduce it, fix it and send it as a patch. I tried many different strategies in last 8 months, but it seems that this one is the most obvious and efficient. After you complete it you will know enough to continue without any advices )

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Re: Question regarding RT patches for ARM
by Fawad Lateef May 18, 2017

May 18, 2017

Hi Eric, On 17 May 2017 at 16:45, Eric Nelson <eric(a)nelint.com> wrote: > Hi Fawad, > > On 05/17/2017 06:40 AM, Fawad Lateef wrote: >> >> On 15 May 2017 at 16:20, Fawad Lateef <fawadlateef(a)gmail.com> wrote: >>> >>> Hi Eric, >>> On 15 May 2017 at 16:12, Eric Nelson <eric(a)nelint.com> wrote: >>>> >>>> Hi Fawad, >>>> >>>>> 发自网易邮箱大师 >>>>> On 05/15/2017 20:44, Fawad Lateef wrote: >>>>> >>>>> Hi All, >>>>> >>>>> I am working on custom i.MX6 quad hardware and using RT patches for >>>>> almost latest stable kernel 4.9 and facing some weird system stall OR >>>>> 'unhandled page fault - exceptions'. >>>>> >>>> >>>> I'm not sure about the unhandled page fault, but the stalls may be >>>> because of the SDMA driver. >>>> >>>> See this patch in the Freescale/NXP community for kernel 4.1: >>>> >>>> https://github.com/Freescale/meta-freescale/blob/master/recipes-kernel/linu… >>>> >>> >>> Thanks for the patch link. I will give it a try. >> >> >> Talked to hardware manufacturer and they applied the patch. >> >> Still that SDMA is only used for NOR flash and only u-boot and its >> environment are stored in nor flash. So not sure if that is going to >> help in any case. >> > > SDMA is used for much more than NOR flash (SSI, USB, and sometimes > UARTs). > Yes SDMA can be used for many devices but in our case its only set to use for NOR (to confirm I also checked sdma interrupts in system and they just 21 or so which happened during boot time). >> So I would really like few more suggestions OR confirmations about ARM >> (cortex-A9 based imx6) (preemept)-RT support/patches are stable and >> can be used for final products. >> > > I don't have any experience with the RT patches on 4.9 or later > kernels, but do know that they're being used on i.MX6 with the > vendor kernels (3.10.x, 4.1.x). > > I believe Alison Chaiken mentioned using them with 4.9 kernels: > http://elinux.org/images/4/42/IRQs-_the_Hard%2C_the_Soft%2C_the_Threaded_an… > https://www.youtube.com/watch?v=-pehAzaP1eg&feature=youtu.be&list=PLbzoR-pL… > Thanks for the video/link. Seems like very informative. Will check it soon. > Regards, > > > Eric Regards, Fawad Lateef

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Importance of kobject
by Madhu K May 17, 2017

May 17, 2017

Hi All, I am kernel newbie, I want to know the importance of kobject, can anybody explain the importance of kobject with an example. Thanks in advance. Madhu

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Re: Question regarding RT patches for ARM
by Fawad Lateef May 17, 2017

May 17, 2017

Hi Eric, On 15 May 2017 at 16:12, Eric Nelson <eric(a)nelint.com> wrote: > Hi Fawad, > >> 发自网易邮箱大师 >> On 05/15/2017 20:44, Fawad Lateef wrote: >> >> Hi All, >> >> I am working on custom i.MX6 quad hardware and using RT patches for >> almost latest stable kernel 4.9 and facing some weird system stall OR >> 'unhandled page fault - exceptions'. >> > > I'm not sure about the unhandled page fault, but the stalls may be > because of the SDMA driver. > > See this patch in the Freescale/NXP community for kernel 4.1: > https://github.com/Freescale/meta-freescale/blob/master/recipes-kernel/linu… > Thanks for the patch link. I will give it a try. > Regards, > > > Eric Regards, Fawad Lateef

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DMA engine doesn't allow callbacks in Interrupt context.
by priyaranjan May 17, 2017

May 17, 2017

Hello All, I have some queries related to the following patch :- Author: Russell King <rmk%2Bkernel(a)arm.linux.org.uk> Date: Mon May 14 15:17:20 2012 +0100 dmaengine: virt-dma: add support for cyclic DMA periodic callbacks Add support for cyclic DMA's periodic callbacks. Drivers are expected to call vchan_cyclic_callback() when a period has completed, which will schedule the tasklet to make the callback into the driver. As callbacks are made from tasklet context, it is important to realise that we don't guarantee a callback for each completed period, but for N completed periods where N may be greater than one. Tested-by: Linus Walleij <linus.walleij(a)linaro.org> Signed-off-by: Russell King <rmk%2Bkernel(a)arm.linux.org.uk> After the patch is submitted there is no guarantee for intermediate callbacks for the cyclic DMA as mentioned in the patch. Please let me know if my understanding is correct. I have a use-case in my audio driver such that all intermediate callbacks are necessary to handle as they get involve in updating other Data structures and triggering other DMAs. Please help me to understand this. Regards, Priyaranjan

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Fwd: Importance of kobject
by Alexander Kapshuk May 17, 2017

May 17, 2017

---------- Forwarded message ---------- From: Alexander Kapshuk <alexander.kapshuk(a)gmail.com> Date: Wed, May 17, 2017 at 10:20 AM Subject: Re: Importance of kobject To: Madhu K <madhu.sk89(a)gmail.com> On Wed, May 17, 2017 at 10:08 AM, Madhu K <madhu.sk89(a)gmail.com> wrote: > Hi All, > > I am kernel newbie, I want to know the importance of kobject, can anybody > explain the importance of kobject with an example. > > Thanks in advance. > Madhu > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > Kobjects play an essential role in the Device Model. The documentation below may be a good starting point in learning about kobjects: https://lwn.net/images/pdf/LDD3/ch14.pdf https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Do…

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SSL certificate with Wrong Hostname
by Narasimha M May 17, 2017

May 17, 2017

Hi All, I am new to check the vulnerabilities. Could some one please tell me about this vulnerability and how to check whether that vulnerability exists. Thanks in advance. -- Narasimha

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Question regarding RT patches for ARM
by Fawad Lateef May 15, 2017

May 15, 2017

Hi All, I am working on custom i.MX6 quad hardware and using RT patches for almost latest stable kernel 4.9 and facing some weird system stall OR 'unhandled page fault - exceptions'. Just want to confirm that "are RT patches for ARM are stable OR they are still experimental?" As I heard from my other colleagues that RT patches are not stable for ARM and should be avoided. Thanks in advance, -- Fawad Lateef

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Re: Question regarding RT patches for ARM
by Fawad Lateef May 15, 2017

May 15, 2017

Hi Sebastian, On 15 May 2017 at 15:47, Sebastian Andrzej Siewior <sebastian.siewior(a)linutronix.de> wrote: > On 2017-05-15 15:09:45 [+0200], Fawad Lateef wrote: >> Hi, >> >> I am talking in general about RT patches. Like downloaded 4.9.20 from >> kernel.org and applied patch "4.9.20-rt16.patch". > > understood > >> On 15 May 2017 at 14:51, GuJiangfei <qiledexin(a)163.com> wrote: >> > Which rt patch do you mean? >> > >> > >> > 发自网易邮箱大师 >> > On 05/15/2017 20:44, Fawad Lateef wrote: >> > >> > Hi All, >> > >> > I am working on custom i.MX6 quad hardware and using RT patches for >> > almost latest stable kernel 4.9 and facing some weird system stall OR >> > 'unhandled page fault - exceptions'. > > and you are sure that this problems are caused by the RT patch or is > there a chance that this is unrelated to the RT patch? > The hardware platform is used by many other projects/products _but_ none of them is using RT patches. So really not sure if its hardware issue, though problem can be seen only in RT version of kernel which is needed for project. >> > Just want to confirm that "are RT patches for ARM are stable OR they >> > are still experimental?" As I heard from my other colleagues that RT >> > patches are not stable for ARM and should be avoided. > > It is stable and I am not aware of any ARM / IMX specific problems. > Ok, thanks. Good to know. I actually want this sort of confirmation as till now "platform/hardware manufacturer" says RT is unstable and should not be used (as newer kernel already have low-latency) > Since this got here from kernelnewbies: I would not recommend the > Preempt-RT patch set to add to any kernel just to have fancy patches. > People use it because they need to fulfill specific requirements which > would not work without it. You might want to check some of the > documentation in the RT-wiki > https://wiki.linuxfoundation.org/realtime/documentation/start > In our case we need RT because few other hardware components (external devices) needs really strict hard-limit and we can't miss that. (BTW I should have not included kernelnewbies in the CC list, but as was asking question in general that's why included). >> > Thanks in advance, >> > >> > -- Fawad Lateef > > Sebastian Thanks, Fawad Lateef

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User space system tap probing
by Gadre Nayan May 11, 2017

May 11, 2017

Hi, I am trying to probe a user space binary: probe process("/usr/sbin/bconfig").function("parse_line") { print("PARSE_LINE\n") printf("Arguments: CP: %s]\n", $cp) print("-----------------------------\n") } Here cp is a char* argument passed to parse_line. Which I need to print. However I get the following error: semantic error: unresolved target-symbol expression: identifier '$cp' at utrace.stp:7:33 source: printf("Arguments: CP: %s]\n", $cp) How can I print parameters passed to function, I am able to do this in kernel space. Thanks

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