March 2020 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

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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Monitor filesystem write to a specific directory?
by Jeffrey Walton March 31, 2020

March 31, 2020

Hi Everyone, I have some build scripts that allow me to install updated developer tools on older machines. It builds and installs tools like Git, Curl and Wget. It also builds dependencies. The scripts can handle about 80 packages. One of those scripts is building a package that is performing a wayward write during 'make install'. It is not using my specified --libdir; instead it appears to hard code ${prefix}/lib. The incorrect hard coded path breaks on Red Hat systems and Solaris. I need to determine the offender. On Windows I would use Process Monitor, run the programs and then filter the events. I'm trying to find a Linux equivalent but neither strace nor ltrace looks like an equivalent. For strace and ltrace it does not look like I can setup a filter and get the process name. How can I monitor filesystem writes to a specific directory? Thanks in advance.

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Requesting Feedback
by Athul Joy March 29, 2020

March 29, 2020

I am Athul Joy. On March 27 I have submitted my first ever patch with the title "[PATCH] Staging: android: fix struct file_operations warning". I have made the patch in /drivers/staging/android/. I have sent the patch to one of the maintainers. I haven't got any feedback from him. I just wanted to know if my patch follows all the guidelines of the kernel community or I missed any steps. I dont know what to do next. This feedback can improve my skills so that I can contribute more to the Linux kernel. Can anyone help me ? Looking forward to hearing from you. Sincerely

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Kernel Development
by Harsh chopra March 29, 2020

March 29, 2020

Hi everyone , I have been studying the given documentations such as Linux Kernel Hacking and Tutorial but what have read so far is related to development of patches for linux kernel but I am interested in linux kernel development from scratch. I came across http://www.dit.upm.es/~jmseyas/linux/kernel/hackers-docs.html but some of the links are not working .Now I am reading Linux Kernel Development by Robert Love . I would like to have your guidance related resources for Kernel Development and also the book I am reading will it help me in the field further.

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Trouble Installing Compiled Kernel
by Nathanael J Grix March 27, 2020

March 27, 2020

Hi, I recently decided to try and make contributions to the kernel. I normally just use windows as my operating system so I decided to set up Slackware to develop on. I thought a good place to start would to actually compile the kernel and install it before I actually make any changes. I ran: make O=/home/nathanael/KernelBuild localmodconfig make O=/home/nathanael/KernelBuild After getting it compiled I ran: bash-4.3$ sudo make O=/home/nathanael/KernelBuild/ install_module install but got this error: make[1]: Entering directory '/home/nathanael/KernelBuild' make[1]: *** No rule to make target 'install_module'. Stop. make[1]: Leaving directory '/home/nathanael/KernelBuild' Makefile:180: recipe for target 'sub-make' failed make: *** [sub-make] Error 2 I have tried looking around but haven't found anything that has been particularly useful in figuring this out. I am not sure what info might be relevant so I'll just let you know that I'm on Slackware 14.2 and trying to upgrade the Kernel from 4.4.208 to 5.6.0 and I am using ELILO instead of LILO. If anyone has any suggestions or can even just direct me to some resources that might have more info on what is going on with make install_module or the error that would be sick. Thanks.

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Re: linux kernel coding style and checkpatch.pl script
by Greg KH March 26, 2020

March 26, 2020

On Thu, Mar 26, 2020 at 04:01:18PM +0300, Konstantin Andreev wrote: > Valdis Klētnieks, 26 Mar 2020 07:13 MSK: > > Don't split literal strings, it means that grepping the source tree for "already registered" fails. Making grep for a string work is more important than shutting up checkpatch. > > On Thu, Mar 26, 2020 at 02:36:23PM +0300, Konstantin Andreev wrote: > > Sic! Grepping is important. Given that, why are kernel functions coded in a > > > > | static int __init loglevel(char *str) > > | { > > > > way, but not old decent unix way: > > > > | static int __init > > | loglevel(char *str) > > | { > > Greg KH, 26 Mar 2020 15:06 MSK: > > Documentation/process/coding-style.rst > > This document does not answer my question. It does not even require > > | static int __init loglevel(char *str) > | { > > style. Here is a relevant part of document: "separate functions with one blank line... EXPORT macro should follow closing function brace ... In function prototypes, include parameter names ... E.g.:" > > | int system_is_up(void) > | { > | return system_state == SYSTEM_RUNNING; > | } > | EXPORT_SYMBOL(system_is_up); > > That's all. Have I overlooked something? Could you, please, share your own point of view? If it's not a specific rule in there, then that means you could do someething crazy like: static int __init loglevel(char *str) { if you were so loony to do so. But, it turns out that when you write your code like that, it's harder to actually find where the function is defined vs. where it is called when greping a codebase. That's why those of us who have been at this for a long time prefer: static int __init loglevel(char *str) { instead. much easier to pick out of a list of "where is this defined" output of 'git grep'. And yes, I know all about ctags and the like, but sometimes you don't have access to that, or don't want to fire it up and have it pre-process things just to look at a specific git tree at the moment. Also, big shoutout to 'vgrep' https://github.com/vrothberg/vgrep which makes using 'git grep' a zillion times easier and is what I rely on all the time. tldr; either way is fine, but putting the return value on the function name line usually makes it easier for others to find your code. Hope this helps, greg k-h

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Re: linux kernel coding style and checkpatch.pl script
by Greg KH March 26, 2020

March 26, 2020

On Thu, Mar 26, 2020 at 02:36:23PM +0300, Konstantin Andreev wrote: > Valdis Klētnieks, 26 Mar 2020 07:13 MSK: > > > > To borrow from Pirates of the Carribean, "They're not exactly rules, they're more like... suggestions..." > > > > Don't split literal strings, it means that grepping the source tree for "already registered" fails. Making grep for a string work is more important than shutting up checkpatch. > > Sic! Grepping is important. Given that, why are kernel functions coded in a > > | static int __init loglevel(char *str) > | { > > way, but not old decent > > | static int __init > | loglevel(char *str) > | { > > unix way? Documentation/process/coding-style.rst

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linux kernel coding style and checkpatch.pl script
by Tomek The Messenger March 26, 2020

March 26, 2020

Hi There is checkpatch.pl script where You can check if You wrote code in your kernel module according to linux kernel style. However can I ignore warning message? WARNING: quoted string split across lines #974: FILE: fpgax67-core.c:974: + dev_err(&pdev->dev, "registration not done, driver is already " + "registered\n"); If I don't split line I will have another warning that 80 characters is exceeded. For sure I can ignore warnings about: WARNING: struct should normally be const #998: FILE: fpgax67-core.c :998: +int fpgax67_unregister(struct platform_device *pdev) For sure all errors must be fixed like: const char* tmp -> change to -> const char *tmp; if( => if ( #insert space Generally I don't know how much warnings should I correct. If it is mandatory or only good practise and I can omit some if it doesn't make sense.

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Finding bugs/issues to work on
by Suraj Upadhyay March 26, 2020

March 26, 2020

Hii newbies, I just started studying for linux-kernel development although I am not completely new to open source technologies. I wanted to clarify my doubts in the following things 1. Where can I find issues/tickets regarding linux-kernel, to work on ? 2. What's the best resource to get started on linux-kernel development ? I started reading kernel-newbies guides, though. Grateful for your time and responses, Yours sincerely, A Kernel-Newbie.

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Should I return NOTIFY_DONE always from restart handler?
by Tomek The Messenger March 24, 2020

March 24, 2020

Hi There is such struct as 'notifier_block'. It has member 'notifier_call' where You assign pointer to your function (handler) and priority. Then You register such notifier block to restart handler list. Then when You type in linux reboot Your function might be invoked (depends on priority you set and if You don't have registered arm_pm_restart function which is typically done through device tree) . My question is should I always return NOTIFY_DONE from my restart handler? Or can I return some error code? In fact this doesn't make sense to return any other code value as Your restart handler has to succeed always in order not to halt system and not to do manually recovery by power off/on.

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