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seq_file calls stop() after show()
by Gaurav Kalra Oct. 5, 2016

Oct. 5, 2016

Hi, I am trying to duplicate the purpose of /proc/pid/io for a homework to understand how procfs / seq_file works. Although there is no mandate to use seq_file but it seems very interesting to me. The aim is to print an output similar to /proc/pid/io but for all processes at once using a custom proc file name "/proc/proc_io". The project is organized as follows: main.c -> It is responsible for kernel module init / deinit sequence.c -> This is where I have put in the processing logic utils.h -> bunch of macros for debugging The debugging logs come as follows: ========= [ +4.814129] <pl_open:15> [ +0.000017] <pl_seq_start:53> [ +0.000003] <pl_seq_start:55> init_task: [ffffffff81e11500] pos: [0] [ +0.000001] <pl_seq_show:103> [ +0.000004] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225a28000] [ +0.000002] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff880225a28dc0] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225a29b80] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff880225a2b700] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225a2d280] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225a2e040] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff880225a2ee00] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225a78000] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff880225a7ee00] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225aa8000] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff880225aa8dc0] [ +0.000001] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff880225aaa940] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225aab700] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff880225aac4c0] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225aad280] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225aaee00] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff880225048000] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff880225048dc0] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff880225049b80] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff88022504b700] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff88022504c4c0] [ +0.000001] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff88022504d280] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff88022504e040] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff8802250f0000] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff8802250f0dc0] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff8802250f1b80] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff8802250f2940] [ +0.000001] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff8802250f44c0] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff8802250f5280] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff8802250f6040] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff8802250f6e00] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_next:72> [ +0.000001] <pl_seq_next:79> n_tsk: [ffff8802251a0dc0] [ +0.000002] <pl_seq_show:103> [ +0.000002] <pl_seq_next:72> [ +0.000002] <pl_seq_next:79> n_tsk: [ffff8802251a1b80] [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_stop:92> [ +0.000276] <pl_seq_start:53> [ +0.000002] <pl_seq_start:55> init_task: [ffffffff81e11500] pos: [1] [ +0.000001] <pl_seq_stop:92> ========= Towards the end, the sequence is as follows: [ +0.000001] <pl_seq_show:103> [ +0.000003] <pl_seq_stop:92> i.e. stop() is called after show(). This is making my output truncated to only first few processes. Although I always return 0 from show(), I fail to understand why stop() is being invoked just after show(). Can you please help me or redirect me somewhere to understand why this is happening? Thank You. Gaurav

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Linux Kernel Based Research Projects
by Shyam Saini Oct. 4, 2016

Oct. 4, 2016

Hi everyone, I'm final year computer science undergraduate student. I want to do my major project based on linux kernel. Would you please suggest me some areas in the kernel which have some projects. To be more specific, I want know on going research areas in kernel. Or some ideas which are not yet implemented. Thanks, Shyam

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memblock_reserve or memblock_remove to reserve a page
by Nikhil Utane Oct. 4, 2016

Oct. 4, 2016

I want to reserve a physical memory page with a fixed PFN. I do not want this page to be used by anyone else. I am calling memblock_reserve() to supposedly reserve the page. I am writing some content into this page. What I see is that during some runs the content of this page is modified (either fully or sometimes partially). In few runs, I see it as intact. Is it expected that even after calling memblock_reserve() the kernel can allocate this physical page for any other purpose? How is memblock_remove() different from memblock_reserve? I tried reading up but didn't see any useful information. What I understood is memblock_remove will completely remove from kernel's allocation mechanism. Should I then be using remove instead of reserve? -Thanks Nikhil

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opinion about fs and gs in linux
by 慕冬亮 Oct. 3, 2016

Oct. 3, 2016

Dear all, When I analyzed one coredump and read some assembly code, I encounter one specific segment register : gs. I googled it and found the following links: [1] http://stackoverflow.com/questions/10810203/what-is-the-fs-gs-register-inte… [2] http://reverseengineering.stackexchange.com/questions/2006/how-are-the-segm… [3] http://stackoverflow.com/questions/6611346/how-are-the-fs-gs-registers-used… In IA32 FS is used by Windows and GS by glibc to reference TLS entry. And in my 32bit linux, I found fs is 0 in my coredump and gs is 0x33. -- My best regards to you. No System Is Safe! Dongliang Mu

1 0

Web Forum Registration Failure
by nick＠nnbits.org Oct. 3, 2016

Oct. 3, 2016

Hello everyone, I tried to register on Kernelnewbies Web Forum, but got this message: You did not provide the correct code for the spam prevention check. Please try again. Would you please help me understand what I was doing wrong? There was no field for spam check and no captcha, only username, email, password, password repeat. I tried two different browsers. I would appreciate any help or support. Thank you. Nick.

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MODULE_DEVICE_TABLE type=of means?
by Muni Sekhar Oct. 3, 2016

Oct. 3, 2016

Hi All, I see that following dma engine driver uses MODULE_DEVICE_TABLE with ‘type=of’. What does ‘type=of’ means? How to trigger this driver’s probe and remove to be called? http://lxr.linux.no/linux+v4.8/drivers/dma/xilinx/zynqmp_dma.c static const struct of_device_id zynqmp_dma_of_match[] = { { .compatible = "xlnx,zynqmp-dma-1.0", }, {} }; MODULE_DEVICE_TABLE(of, zynqmp_dma_of_match); static struct platform_driver zynqmp_dma_driver = { .driver = { .name = "xilinx-zynqmp-dma", .of_match_table = zynqmp_dma_of_match, }, .probe = zynqmp_dma_probe, .remove = zynqmp_dma_remove, }; module_platform_driver(zynqmp_dma_driver); MODULE_AUTHOR("Xilinx, Inc."); MODULE_DESCRIPTION("Xilinx ZynqMP DMA driver"); -- Thanks, Sekhar

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Virtual Address Space
by Madhu K Oct. 3, 2016

Oct. 3, 2016

Hi All, This is to understand the Virtual address space.Basically who generates the virtual addresses CPU or GNU compiler? Thanks Madhu

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Booting of Linux kernel
by Er Krishna Oct. 2, 2016

Oct. 2, 2016

Hi all I have a basic question for understanding : If we want to boot the Linux kernel without bootloader what needs to be done? In other words what all the core subsystem like memory and all needs initialisation by bootloader and if bootloader is not there then how to do it ? Thanks Krishna

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Re: Options for adding I2C devices and how-to
by vibnwis Oct. 1, 2016

Oct. 1, 2016

> > > https://events.linuxfoundation.org/sites/events/files/slides/petazzoni- > device-tree-dummies.pdf > check page 29/45 > >> >> > This is awesome. Very helpful. I would recommend to get your hands dirty. Start playing with userspace i2c > tools > to get an idea and also there are many raspberry project out there to get > you started with. > Agreed and thanks for the advice.

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Re: Options for adding I2C devices and how-to
by vibnwis Oct. 1, 2016

Oct. 1, 2016

Many thanks Anish for answering my doubts. > You need to find out the device address of your device. > find out which device is not connected and connect your device on that bus > and change the device tree to replace the device address. > Would you elaborate on device tree, please? > You can certainly use i2c_detect and i2c_get user space tools to work with > your device. However is there is a existing kernel space i2c device on that > bus then it will certain lead to bus hogging problems. > > Besides i2c_detect and i2c_get user space tools. I think one can also change two existing GPIOs for SDA and SCLK respectively and using software logics to drive them as I2C bus. I presume the entire GPIOs are able to be mapped for user space, is it not? > Feel free to add any comments or suggestions. > Please add information about your device and kernel version which you are > trying to use. May be there is already a driver for it in open source. > > I am doing some sort research at the moment. I like to know the whole picture before putting my hand on. Hence, at the moment it is pure on papers. However, the kernel version should be 2.6.38 and above. Nevertheless, since I have Pandaboard rev B , and Raspberry 3, I will definitely things that available for these two. Does it make sense? Thanks in advance.

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