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How do the kernel boot parameters work (especially "toram")?
by Gueven Bay Aug. 27, 2021

Aug. 27, 2021

Hello, With kernel boot parameters I mean the arguments you give on the grub command line to the kernel. Just like "toram" which on some distros work and on many doesn't. I googled but only found webpages listing the possible boot parameters and maybe explaining what they do, but none where it was explained _how_ they work. Does a boot parameter make the kernel call a script? Does a boot parameter reference a function inside the kernel? If some distros seem to allow a specific boot parameter what did they do to their distros kernel to make this parameter work? And which module or which part of the kernel takes the boot parameters as input to do the appropriate things? For example: It seems that Centos (8) does not suppport "toram" (allowing to load the whole OS into RAM), at least on my machine. Okay, what should or can I do to get my (Centos) kernel to accept this? Writing a script? Patching something? (Maybe my questions are not really clear, just ask me, please.) Thanks.

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surround complex macros in ()
by daniel watson Aug. 26, 2021

Aug. 26, 2021

let me know if this is the right place to ask. i recently tried to make a commit adding parentheses around a macro value. https://lore.kernel.org/linux-staging/20210817043038.GA9492@challenge-bot.c… it was rejected as "This is not a real change that is needed." at first, i thought this meant that the code would be identical with and without parentheses surrounding a complex macro's definition, when the macro is just typecasting an expression. but then i came up with code where having parens or not changes the meaning of the code. -------delete-me.c-------- #define with ((int)a) #define sans (int)a void main(void){ int b = 0; with++; sans++; } -------delete-me.c-------- -------terminal-------- $ gcc -o delete-me delete-me.c delete-me.c: In function ‘main’: delete-me.c:7:7: error: lvalue required as increment operand 7 | with++; | ^~ -------terminal-------- the compiler complains about the macro defined with parentheses, and does not have a problem with the other macro defined sans parentheses. this is only a compile time difference, and maybe that's the only possible difference that could be made by the parentheses. i'm curious if there's a way to know for sure that there exists no possible expression with such a macro in it that would cause a more subtle difference. for example, how do i rule out the possibility that the code could compile and have a different value than expected at runtime? as a side note, i signed up for the kernelnewbies mailing list, and i do not see any messages in my inbox, except a reply to a message i sent out. i checked here in some expression http://lists.kernelnewbies.org/pipermail/kernelnewbies/ and do not see the message i sent, or the reply to it. am i seeing the right thing? did i sign up correctly? is that the right page to view the mailing list messages online? thanks!

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Which tool to use for Mesh Testing
by Raul Piper Aug. 24, 2021

Aug. 24, 2021

Hello , Which tool I can use for Ble Mesh testing, meshctl or gatt-mesh or any other ? I followed few mails and came to know meshctl is not fit for use. Please advice. I want to test both PB-ADV and PB-GATT. Thanks in advance ! Regards, Rp

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Re: how do you find the subsystem of a file?
by daniel watson Aug. 22, 2021

Aug. 22, 2021

On Sat, Aug 21, 2021 at 12:30:27AM -0700, daniel watson wrote: > i wrote a patch that got rejected because it did not apply cleanly to > the tree of greg kh > https://lkml.org/lkml/2021/8/18/304 > > the file i modified is > drivers/staging/rtl8723bs/include/rtl8192c_recv.h > > get_maintainer.pl gave me the list of emails to send the patch to, > and i used it for that purpose. the file > Documentation/process/submitting-patches.rst says to see the T: entry > for the subsystem in MAINTAINERS to find the right tree to base the > patch on. i tried searching through MAINTAINERS and found that there > are a few subsystems that start with RTL8*. > > greg kh is listed a few times in MAINTAINERS, so i'm not able to find > the exact tree to start with by looking for the maintainer. > > is there a systematic way of finding the subsystem, given a file? > > in addition, how do i know what branch to use? the T: entries have a > repo, but not a branch name. > > thanks! > :wq, danny answering my own question, the output of git log --oneline -1 <path> should have the subsystem listed at the beginning. thanks! C-x C-c, danny

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Request for login to update https://kernelnewbies.org/FirstKernelPatch
by Philipp Hortmann Aug. 21, 2021

Aug. 21, 2021

Just following the "FirstKernelPatch" and found the following line: apt-get install python-ply python-git that needs to be replaced by: apt-get install python3-ply python3-git Please provide me a login or edit yourself.

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How to implement waiting until processing is done by a device..
by ckim＠etri.re.kr Aug. 20, 2021

Aug. 20, 2021

Hello, We are developing a compute accelerator and I'm not sure which is the best or normal way to implement the waiting method for the application until the computing is finished by the accelerator. The application first sets up input data and configuration for the accelerator on the memory. It then calls an ioctl which sets up the registers and it calls another ioctl which trigger the accelerator. My idea is : * The application process goes into wait queue after calling the second ioctl by telling the OS "keep me in the wait queue and wake me up when 'this' signal comes'. * The driver's ISR process sends a signal to the sleeping user process when processing the 'computing complete' interrupt. Does this make sense? (Can I define and use a signal for this purpose?) And if it does, what function calls should I use? I would appreciate sending me any link for suggested reading. It should be possible to use accelerator for multiple processes at the same time, but I think for now we can just do with single application. Thanks! Chan Kim

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Eudyptula Challenge.
by David K Aug. 20, 2021

Aug. 20, 2021

Hello, It is my plan to share some, if not all, of my material from Eudyptula challenge here mostly with the intent of getting critique. This should not be against any Eudyptula challenge rules as a lot of people have already shared their solutions to the challenge on Github and probably other places. Since email is the accepted way of contributing to Linux kernel development and a lot of other open source projects, this is my preferred way of sharing my solutions and possibly getting critique. It is my hope that this is not against any list rules. This looks like the case to me and would it happen that this is not the case, any heads up would be much appreciated. Regards, David.

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Re: kmalloc - Address is not consecutive
by Lloyd Aug. 19, 2021

Aug. 19, 2021

Thanks a lot, it worked :) On Thu, Aug 19, 2021 at 7:00 PM ckim <ckim(a)etri.re.kr> wrote: > Hi! this one is easy :) > For printing pointer in kernel space, you should use %px not %p as format > specifier. I heard this is for security reason(?). > Chan Kim > > 내 Galaxy에서 보냄 > > > -------- 원본 이메일 -------- > 발신: wuzhouhui <wuzhouhui14(a)mails.ucas.ac.cn> > 날짜: 21/8/19 오후 9:17 (GMT+09:00) > 받은 사람: Lloyd <lloydkl.tech(a)gmail.com>, kernelnewbies(a)kernelnewbies.org > 제목: Re: kmalloc - Address is not consecutive > > > > On 8/19/21 6:54 PM, Lloyd wrote: > > Hi, > > > > I am trying to print the address of consecutive locations in a > > memory allocated using kmalloc. It prints non contiguous addresses! I > > tried with kmalloc_array, and normal array on stack, I got the same > > result. May I know the reason? The code fragment for array and result > > are given below. > > > > uint8_t MyArray[100]={'0'}; > > printk(KERN_INFO "\nAddress is-> %p\n",&MyArray[0]); > > printk(KERN_INFO "\nAddress is-> %p\n",&MyArray[1]); > > printk(KERN_INFO "\nAddress is-> %p\n",&MyArray[2]); > > > > > > [ 8684.613909] Address is-> 00000000b3330991 > > [ 8684.613914] Address is-> 000000000519068c > > [ 8684.613915] Address is-> 00000000e448ca76 > > > Quoted from Documentation/core-api/printk-formats.rst: > > A raw pointer value may be printed with %p which will hash the address > > before printing. The kernel also supports extended specifiers for > printing > > pointers of different types. > So the address printed neither logical nor physical address. > > > Thanks a lot, > > Lloyd > > > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >

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kmalloc - Address is not consecutive
by Lloyd Aug. 19, 2021

Aug. 19, 2021

Hi, I am trying to print the address of consecutive locations in a memory allocated using kmalloc. It prints non contiguous addresses! I tried with kmalloc_array, and normal array on stack, I got the same result. May I know the reason? The code fragment for array and result are given below. uint8_t MyArray[100]={'0'}; printk(KERN_INFO "\nAddress is-> %p\n",&MyArray[0]); printk(KERN_INFO "\nAddress is-> %p\n",&MyArray[1]); printk(KERN_INFO "\nAddress is-> %p\n",&MyArray[2]); [ 8684.613909] Address is-> 00000000b3330991 [ 8684.613914] Address is-> 000000000519068c [ 8684.613915] Address is-> 00000000e448ca76 Thanks a lot, Lloyd

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[RFC PATCH v3 00/18] Add block device LED trigger
by Ian Pilcher Aug. 19, 2021

Aug. 19, 2021

Ridiculous or not, here is version 3 of the block device trigger for "freaking blinkenlights". It addresses basically all of the points raised in response to the v2 patchset. * The main body of the code is moved from the block directory into the LED triggers directory (drivers/leds/trigger/ledtrig-blkdev.c) The downside of this is that it requires adding an API to the block subsystem - get_disk_by_name() - which allows the trigger code to resolve a gendisk when asked to monitor it. I know of no good way to do this today, and I don't know of a good way to implement the sysfs API requested by Pavel and Marek without something like this API. Other than that, changes to the block subsystem are as minimal as I can make them - a single pointer added to struct gendisk and init/cleanup calls when a gendisk is added or deleted. * This also implements Marek's suggestion of periodically checking devices for activity, rather than directly blinking LEDs in the I/O path. This change has the unanticipated benefit of making the trigger work on pretty much all types of virtual block devices (device mapper, MD RAID, zRAM, etc.), as well as NVMe SSDs. * Relationships between devices and LEDs are now many-to-many. An LED can monitor multiple devices, and multiple LEDs can monitor any one device. The current "associations" are reflected in two sysfs directories. - /sys/class/leds/<led>/block_devices contains links to all devices associated with an LED, and - /sys/block/<disk>/blkdev_leds contains links to all LEDs with which the device is associated. (The latter directory only exists when the device is associated with at least one LED.) * Each LED can be set to show read activity, write activity, or both. Discards and cache flushes are considered to be writes, as they affect the state of the device's non-volatile storage. Ian Pilcher (18): docs: Add block device (blkdev) LED trigger documentation block: Add get_disk_by_name() for use by blkdev LED trigger ledtrig-blkdev: Add file (ledtrig-blkdev.c) for block device LED trigger ledtrig-blkdev: Add misc. helper functions to blkdev LED trigger ledtrig-blkdev: Periodically check devices for activity & blink LEDs block: Add LED trigger pointer to struct gendisk ledtrig-blkdev: Add function to initialize gendisk ledtrig member ledtrig-blkdev: Add function to remove LED/device association ledtrig-blkdev: Add function to disassociate a device from all LEDs block: Call LED trigger init/cleanup functions ledtrig-blkdev: Add function to associate a device with an LED ledtrig-blkdev: Add sysfs attributes to [dis]associate LEDs & devices ledtrig-blkdev: Add blink_time & interval sysfs attributes ledtrig-blkdev: Add mode (read/write/rw) sysfs attributue ledtrig-blkdev: Add function to associate blkdev trigger with LED ledtrig-blkdev: Add function to disassociate an LED from the trigger ledtrig-blkdev: Add initialization function ledtrig-blkdev: Add config option to enable the trigger Documentation/ABI/testing/sysfs-block | 9 + .../testing/sysfs-class-led-trigger-blkdev | 48 ++ Documentation/leds/index.rst | 1 + Documentation/leds/ledtrig-blkdev.rst | 132 +++ block/genhd.c | 28 + drivers/leds/trigger/Kconfig | 9 + drivers/leds/trigger/Makefile | 1 + drivers/leds/trigger/ledtrig-blkdev.c | 770 ++++++++++++++++++ include/linux/genhd.h | 13 + include/linux/leds.h | 20 + 10 files changed, 1031 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-led-trigger-blkdev create mode 100644 Documentation/leds/ledtrig-blkdev.rst create mode 100644 drivers/leds/trigger/ledtrig-blkdev.c -- 2.31.1

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