February 2020 - kernelnewbies@kernelnewbies.org

How to make /dev/ttyACM0 (and friends) exclusive?
by Jeffrey Walton Oct. 11, 2020

Oct. 11, 2020

Hi Everyone, I'm trying to trackdown a problem using my dialup modem. I have a program that opens the modem and watches caller id's. It flashes the hook when a telemarketer calls. It works well until... When another program opens the modem then my program starts reading intermittent responses intended for the other program. I cannot seem to open the device in exclusive mode. The current open is (I also tried with O_EXCL): int modem = open(device_path, O_RDWR | O_NOCTTY | O_SYNC); I'm not sure if it because udev configures the device incorrectly or the kernel driver is configured incorrectly. Or maybe it is impossible to do. Does anyone know how I can make the device exclusive? Thanks in advance.

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New text
by Ruben Safir March 15, 2020

March 15, 2020

is there currently a rfecommended text to learn kernel development from? -- So many immigrant groups have swept through our town that Brooklyn, like Atlantis, reaches mythological proportions in the mind of the world - RI Safir 1998 http://www.mrbrklyn.com DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002 http://www.nylxs.com - Leadership Development in Free Software http://www2.mrbrklyn.com/resources - Unpublished Archive http://www.coinhangout.com - coins! http://www.brooklyn-living.com Being so tracked is for FARM ANIMALS and extermination camps, but incompatible with living as a free human being. -RI Safir 2013

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Need help to get started
by m vivek March 2, 2020

March 2, 2020

Hi, I just joined the mailing list. Excited to contribute to linux kernel but finding it difficult to figure out where to start. Any help would be appreciated. PS: I've gone through some articles online which suggest to start with improving the coding style and refer to TODO from drivers/staging/. Thanks -Vivek.

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syfs question
by Sadanand Warrier Feb. 28, 2020

Feb. 28, 2020

If I call device_create with a existing class the device lands up in /sys/devices/virtual. Using device_add I could populate the parent of the device and leave the class empty or provide a class and get the device to be created in the parent directory. What exactly is the significance of the" /sys/devices/virtual" directory? Is this meant to carry devices of a specific type say something that is divorced from actual hardware? Secondly a device created under /sys/devices/virtual has a uevent file that is populated like this. -bash-4.2$ cat uevent MAJOR=13 MINOR=63 DEVNAME=input/mice -bash-4.2$ A device in a specific PCI slot has something like this instead.. -bash-4.2$ cat /sys/devices/pci0000:00/0000:00:02.2/0000:03:00.3/net/eth1/uevent INTERFACE=eth1 IFINDEX=3 How is this file populated? Is it done by udev or is this done via a kernel call? Thanks S

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.config
by Enzo Desiage Feb. 23, 2020

Feb. 23, 2020

Hi all, <https://twitter.com/enzo_dancing> I have just finished reading most of "The Linux Kernel in a Nutshell". 1. I wish I knew about this book two weeks ago 2. I'm currently recompiling my kernel in a VM, by having copied the base .config file from /boot as it's been recompiling, for now, more than an hour, I started having questions and carried on reading the book hoping to find answers. Turns out I don't need every modules and driver that Ubuntu has in its initial .config file for my VM. Having understood that and found all the modules I actually need (thanks find_all_modules.sh). I'm trying to devise a strategy to take the output of that script and make a brand new minimal .config file. However, the only solution I've found is doing it manually via make menuconfig. This seems to be a rather long process, which I wouldn't mind doing if there aren't any other alternatives. Is there any other way? Thanks, Enzo

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HWCAP for SHA-1 and SHA-256
by Jeffrey Walton Feb. 23, 2020

Feb. 23, 2020

Hi Everyone, I'm having trouble finding the HWCAP_* or HWCAP2_* for SHA-1 and SHA-256 on x86 machines. Poking around Torvald's GitHub does not reveal them in either auxvec.h or hwcap2.h. Also see https://github.com/torvalds/linux/tree/master/arch/x86/include/uapi/asm. Grepping my local machine (x86_64) provides them for arm64, but not x86 (WTF?): $ grep -IR HWCAP2_ /usr/include /usr/include/x86_64-linux-gnu/asm/hwcap2.h:#ifndef _ASM_X86_HWCAP2_H /usr/include/x86_64-linux-gnu/asm/hwcap2.h:#define _ASM_X86_HWCAP2_H /usr/include/x86_64-linux-gnu/asm/hwcap2.h:#define HWCAP2_RING3MWAIT (1 << 0) What are the HWCAP_* or HWCAP2_* to use for SHA-1 and SHA-256 on x86 machines? Thanks in advance.

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Kernel debugging
by Pankaj Vinadrao Joshi Feb. 22, 2020

Feb. 22, 2020

Hi, I am using linux 5.4.3 with our custom Yocto distro on RISC v machine i want to get kernel crash log(hard panic) since RISC v does mot have support for the kxec how i can collect the crash logs?

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uxfs review
by Valentin Vidić Feb. 20, 2020

Feb. 20, 2020

On Wed, Feb 19, 2020 at 04:36:10PM -0500, Valdis Klētnieks wrote: > (Of course, if you're trying to get a 2.6.12 driver working on 5.6... you may decide > that it's time to start drinking heavily :) Now that you mention 2.6 :), I've been trying to update this uxfs filesystem from an old book[1] for modern kernels: https://github.com/vvidic/uxfs/ It currently builds and seems to work but it could probably use a review if someone has a bit of time? I can post the diff here if that would be easier. [1] Steve D. Pate, UNIX Filesystems, 2003. -- Valentin

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spaces after typecasts?
by Anuz Pratap Singh Tomar Feb. 19, 2020

Feb. 19, 2020

Hi all, I don't see anything in coding guidelines about spaces after typecasts i.e. (char *)x; vs (char *) x;. Typecasts are considered keywords or not? given you could typecast to a non C keyword as well? -- Thank you Warm Regards Anuz

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PCIe hotplug
by Sadanand Warrier Feb. 13, 2020

Feb. 13, 2020

Hi I had question about PCIe hotplug. We have hardware that is connected to the host by means of two PCIe switches. i.e. the host sees a PCIe switch connected to one of its buses and on the far side of that switch another PCIe switch which has a PCIe device. It is possible that this device does not train its host facing PCIe links before the server enumerates down its PCI bus and reaches those links. It is also possible the PCIe switch to which the device is attached has not been able to train its own links before server enumeration. Is PCIe hotplug built to work on schemes like this? Let us assume that the hardware has been designed to trasmit a presence signal once the links are trained but this could happen after the server enumeration? Incidentally does the server take advantage of the BIOS/UEFI enumeration? Thanks S

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