August 2021 - kernelnewbies@kernelnewbies.org

Re: Kernel 4.14: Using dm-verity with squashfs rootfs - mounting issue
by Pintu Agarwal Aug. 30, 2021

Aug. 30, 2021

On Wed, 21 Jul 2021 at 22:40, Mikulas Patocka <mpatocka(a)redhat.com> wrote: > > > > > > Try to set up dm-verity with block size 512 bytes. > > > > > > I don't know what block size does squashfs use, but if the filesystem > > > block size is smaller than dm-verity block size, it doesn't work. > > > > > Okay thank you so much for this clue, > > It seems we are using 65536 as the squashfs block size: > > 65536 is the compression block size - it is unrelated to I/O block size. > > There's a config option SQUASHFS_4K_DEVBLK_SIZE. The documentation says > that it uses by default 1K block size and if you enable this option, it > uses 4K block size. > Okay it seems this config is set in our case: CONFIG_SQUASHFS_4K_DEVBLK_SIZE=y So, with this the squashfs and dm-verity block size exactly matches (4K) > So, try to set it. Or try to reduce dm-verity block size down to 1K. > Okay we are trying this. Thank you so much!! Regards, Pintu

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Get notification when a block device is mounted.
by Douglas Su Aug. 30, 2021

Aug. 30, 2021

Hi, all: I want to get notified when a block device is mounted, and after some google searches, it seems a syscall named "mount_notified()" existed before but was removed in the latest kernel. For the latest kernel, is there any system call or other mechanisms cater this purpose? Thanks

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USB/HID: Device with multiple interfaces
by José Expósito Aug. 29, 2021

Aug. 29, 2021

Hi all, I'm trying to solve an issue with a mouse that only reports battery over Bluetooth. I hope you can help me. When connected over Bluetooth, the mouse registers one HID descriptor containing both mouse and power device collections. However, when it's connected over USB, I can see using lsusb that 3 interfaces are available and, unlike with Bluethoot, the HID descriptors containing mouse and power device are in different interfaces. The battery percentage is not reported in this case. So far I've been able to get the battery percentage in the driver by manually calling devm_power_supply_register and submitting an URB. My question is: since the HID descriptors with the power device collection is present but in a different interface, is there a way to associate both interfaces to the same physical device and get the battery percentage automatically? Thank you very much in advance, Jose

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Update of kernelnewbies.org/FirstKernelPatch required
by Philipp Hortmann Aug. 29, 2021

Aug. 29, 2021

Hi, I am just following the "FirstKernelPatch" instructions and found out that yahoo as email account does not work anymore. Reason is that the Security Setting "Allow apps that use less secure sign-in" does not exist anymore. For gmail it is required to activate the option "Allow apps that use less secure sign-in" to be able to conduct the following steps of the instructions. This hint is missing. A proposal from "greg at kroah.com Sun Dec 27 03:50:21 2020" proposes to use fastmail.fm fastmail.fm is not for free and also not mentioned in the "FirstKernelPatch" instructions. Please do not let all newbies fall into this trap. Please provide me a login or edit yourself. Thanks for your support. Bye Philipp

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Contributing to drivers/staging area
by Len Baker Aug. 27, 2021

Aug. 27, 2021

Hi Greg, I am a kernel newbie in the path to find an area where to contribute on. I have sent some patches before (simple ones) but I would like to find some driver to contribute on and if possible mantain in the future. Due to the big amount of drivers in staging, and my lack of experience and specific hardware: Are there any driver in the staging area that not requires specific hardware? I have only access to an old laptop with 4 processors: vendor_id : GenuineIntel cpu family : 6 model : 37 model name : Intel(R) Core(TM) i3 CPU M 370 @ 2.40GHz Can I find a driver to contribute on with my machine requirements? If yes, any advise to select one would be greatly appreciated. I would like to improve the driver until get it out from staging ;) And then maintain it. Another option for me if there are no drivers would be create one from zero. But I don't have any idea of useful driver. Any advise and ideas here would be also great appreciated. Thanks in advance. Regards, Len

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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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