September 2016 - kernelnewbies@kernelnewbies.org

where is __percpu_seg initialized?
by 落痕 March 28, 2018

March 28, 2018

Hi all: I knew the kernel implement the per-cpu variable via __percpu_seg. For example on x86 architecture, it's defined as: #ifdef CONFIG_X86_64 #define __percpu_seg gs #define __percpu_mov_op movq #else #define __percpu_seg fs #define __percpu_mov_op movl #endif But I'm curious where __percpu_seg is initialized?? I fail to find the relative code. Thanks.

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How to handle Hotplug with UIO userspace driver
by Mandeep Sandhu Sept. 28, 2017

Sept. 28, 2017

Hi All, We're working on a custom PCIe based hardware, which can be hotplugged into the system. We're using the UIO approach of having a minimal kernel driver which basically handles the interrupt and provides a mmap of the device memory to userspace and userspace driver which mmap's the provided memory and manages the device. We're using systemd and udev rules to spawn off a user process whenever the hardware is plugged into the system. Now my question is, how can we gracefully inform the userspace process if someone pulls out the hardware (sitting on a PCI slot). Even with full hotplug support, there can always be a case of "surprise removal", where someone yanks the board without going through the whole "attention button" routine. While the kernel driver has no problem with hot-removal, I see that if I "unregister" our UIO driver in response to the removal, then the mapping for the hardware's physical memory would become "invalid" (done by UIO on unregsiter). This could possibly cause the user-space process to crash due to illegal memory access. Is there a "standard" way to handle this scenario, i.e for hotpluggable hardware using UIO? Basically, we'd want to "unregister" the UIO device only after the userspace process is informed of the removal so that it could unmap/close the device and exit gracefully. We could try doing it using some systemd trick, where we put a dependency on one of the UIO created files (/dev/uioX), so that when the file is destroyed, systemd could kill/shutdown the process. Although, there's no guarantee that the userspace process won't try to access the mmaped space during that interval, so this isn't a reliable solution either. Any hints, thoughts? Thanks., -mandeep

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What are need to makes humidifier?
by 윤영석 April 1, 2017

April 1, 2017

Hi, I want to make own humidifier. What sensor need when making humidifier?? humidity indicator (detecting humidity), ultrasonic waves maker?? Please shares your wisdom to me. Thanks. Best regards.

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Error reading /dev/mem
by Paddie O'Brien Oct. 10, 2016

Oct. 10, 2016

Hi, I have a system call that maps virtual to physical addresses. I have disabled CONFIG_STRICT_DEVMEM and am reading from /dev/mem to verify that the contents of the syscall-returned physical address match the contents of the virtual address. It works fine up to a point. Reading beyond byte 935321597 in /dev/mem throws a "bad address" error. Not sure it's relevant but I'm running on virtual box and specifying 1GB of RAM. Tried with 2GB of RAM and hit the same problem. Any idea why I can't read beyond the above point? Thanks.

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[PATCH] INITEST: Documentation: Explains how INITEST works.
by Amit Kumar Oct. 5, 2016

Oct. 5, 2016

Signed-off-by: Amit Kumar <free.amit.kumar(a)gmail.com> This is a test patch. Is this patch in right format? --- Documentation/initest.txt | 7 +++++++ 1 file changed, 7 insertions(+) create mode 100644 Documentation/initest.txt diff --git a/Documentation/initest.txt b/Documentation/initest.txt new file mode 100644 index 0000000..eed4124 --- /dev/null +++ b/Documentation/initest.txt @@ -0,0 +1,7 @@ +INITEST + +1) This is the same user space program /sbin/init, but for the purpose of testing kernel system calls. + +2) It will also use testing drivers to test internal kernel API. + +3) This is a test patch. -- 2.7.4

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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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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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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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Does a kernel developer need a hardware to do kernel development?
by Amit Kumar Oct. 1, 2016

Oct. 1, 2016

Hi, (1) I want to work on staging drivers. But I've two questions, Does a kernel developer need a hardware (e.g. board) to do kernel development? (2) I'm able to send patch using sendmail and git. I'm able to apply patch using git-am. But unable to setup mutt to download patch from this emailid. How to setup mutt to download patches? -- Regards, Amit Kumar Twitter: @freeark1 Only Numbers Can Command.

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