March 2021 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

make menuconfig
by Martin Herdeis March 25, 2021

March 25, 2021

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How to switch between installed kernel and developed kernel
by Gidi Gal March 25, 2021

March 25, 2021

Hello, I am new to kernel development, currently working on https://kernelnewbies.org/FirstKernelPatch. I reached the step "Install your changes" in "Modifying a driver on native Linux". I would like to separate my developed kernel and my installed kernel and to switch between the two in order to test my changes. I am not sure that my tutorial explains how to do that. If you have a link that proposes a workflow for this request (or if my tutorial does explain this workflow and I'm missing the exact paragraph that does that) please let me know. Thanks, Gidi

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"module:find_symbol: Failed to find symbol ....." not so bad.
by jim.cromie＠gmail.com March 25, 2021

March 25, 2021

so when I enable the pr_debug()s in kernel/module, and boot that kernel, I get a raft of messages (~800), like : [ 110.072535] module:find_symbol: Failed to find symbol drm_scdc_get_scrambling_status [ 110.072538] module:find_symbol: Failed to find symbol drm_scdc_read [ 110.072541] module:find_symbol: Failed to find symbol drm_scdc_set_high_tmds_clock_ratio [ 110.072545] module:find_symbol: Failed to find symbol drm_scdc_set_scrambling [ 110.072548] module:find_symbol: Failed to find symbol drm_scdc_write [ 110.072551] module:find_symbol: Failed to find symbol drm_self_refresh_helper_alter_state [ 110.072553] module:find_symbol: Failed to find symbol drm_self_refresh_helper_cleanup What is the potential importance of these ? clearly if it were a real problem, it wouldnt just be a debug message. Is there anything to fix here, either in local config, or in code ?

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"Invalid signature" issue on dev kernel launch
by Gidi Gal March 24, 2021

March 24, 2021

Greetings, After receiving a lot of information regarding my query on how to switch from installed to dev kernel (thank you to all the people that shared their knowledge on this subject), I am now facing "invalid signature" error when I reboot with my installed dev kernel. I shared the logs for the build, install and also .config and x509.genkey in the following link <https://drive.google.com/drive/folders/1mVUzrF_5MM4H1x0bLacprvkrXaKtFm6V?us…> . Please let me know what additional information can help to solve this issue. I am following the instructions in https://kernelnewbies.org/FirstKernelPatch and I am at the step where I am supposed to verify that a printout was added to the log after I reboot my dev kernel. Thanks, Gidi

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Re: How to switch between installed kernel and developed kernel
by Aruna Hewapathirane March 23, 2021

March 23, 2021

On Tue, Mar 23, 2021 at 10:37 AM Gidi Gal <gidi.gal.linux(a)gmail.com> wrote: > Thanks Aruna and Valdis for your replies. > > Use : linux-check-removal <uname-r of your kernel to remove> >> > > I tried to use it on my kernel. It did not seem to work - I still see the > files in /boot. I assume it is because my kernel is not signed properly. > When I launch "dpkg --list | grep linux-image" I don't see my kernel in > the list. When I reboot I still get an "invalid signature" error. I attach > the build log, install log and .config file and x509.genkey file. Please > let me know what additional input can help to analyze this issue. > > dpkg -i and make install are two very different beasts. See this answer it will help you to understand why you are seeing the files in boot. https://askubuntu.com/questions/1118896/software-installation-with-dpkg-i-v… The safest way would be to identify which kernel you want to remove first. Change into /boot then use rm to delete the files one by one. Then run sudo update-grub2 and reboot. And your good to go. > Seriously - if you're not comfortable with that level of sysadmin >> procedures, >> maybe you shouldn't be a kernel hacker... >> > > Once you are comfortable with compiling + linking/building +running a >> custom kernel >> what is preventing you from writing 'your own command' to do exactly that >> ? Say a bash >> script ? Or Python program ? >> > > I gave up for now and prepared bash script for removing the files, based > on the information in > https://www.cyberciti.biz/faq/debian-redhat-linux-delete-kernel-command/ > (see "A note about custom compiled Linux kernel" section). In my opinion, > if Makefile supports install, it should support uninstall as well. Please > let me know whether it sounds like a worthy enhancement or a wrong > expectation. > > Have a look at the make install and make clean sections in the Makefile. Again nothing to stop you from having a 'delete' or 'remove' target eh ? :-) > Thanks, > Gidi > > > > > On Tue, Mar 23, 2021 at 6:29 AM Aruna Hewapathirane < > aruna.hewapathirane(a)gmail.com> wrote: > >> On Mon, Mar 22, 2021 at 9:17 PM Valdis Klētnieks <valdis.kletnieks(a)vt.edu> >> wrote: >> >>> On Tue, 23 Mar 2021 00:01:22 +0200, Gidi Gal said: >>> >>> > Many thanks for your reply, Aruna. Is there a way to remove the >>> installed >>> > '5.12.0-rc3-GIDI_DEV+' kernel ? >> >> >> Yes there are 'many' ways to remove a kernel :-) >> >> A reverse command for the 'sudo make >>> > modules_install install' command ? I found this link which explains >>> how to >>> > do it manually ( >>> > >>> https://www.cyberciti.biz/faq/debian-redhat-linux-delete-kernel-command/ >>> ), >>> > I wonder if there is a safer way. >>> >> >> Type linux into your shell then press the 'tab' key twice.. you will see >> a list of commands. >> >> Use : linux-check-removal <uname-r of your kernel to remove> >> >> Once you are comfortable with compiling + linking/building +running a >> custom kernel >> what is preventing you from writing 'your own command' to do exactly that >> ? Say a bash >> script ? Or Python program ? >> >> >>> I can't speak for Debian, but I've used both the RedHat rpm method and >>> just >>> using the 'rm' command for self-bullt kernels since the 2.5.47 kernel or >>> so >>> (Egads, that was November 2002). As long as you follow the directions, >>> you >>> should be OK. 'rm' can get dangerous if you get over-exuberant with >>> using '*' >>> characters, but you already knew that, right? :) >>> >> >> If you have to use rm always use it with the -i flag. Always prompt >> before removal. >> >> >>> And if you followed my recommendation and back up /boot, you'll be all >>> set to restore whatever you mess up. >> >> >> Listen to Valdis in this case and follow orders religioulsy. Back up not >> just /boot but anything >> and everything that is important for you. >> >> >>> The running kernel will work just fine >>> as long as you don't reboot. And unless you did 'rm /boot/*', you should >>> have >>> at least one usable kernel left... >>> >>> Seriously - if you're not comfortable with that level of sysadmin >>> procedures, >>> maybe you shouldn't be a kernel hacker... >> >> >> Do not listen to Valdis in this case as we were all newbies at one time >> like Dan Carpenter told me >> which I will remember to my dying day. Do not let anyone tell you what >> you can or cannot do when it >> come's to the kernel because believe me like me you will find out over >> time the kernel is a living thing that >> has very subtle ways of informing you when you did something and it is >> not happy :-) >> >> So compile away to your hearts content and go ahead and break things like >> I did that is actually a very good way to learn. >> And listen to more experienced folk like Valdis who probably knows more >> about all the subsystems than anyone. But if anyone tells you >> you should not be a kernel hacker then prove them wrong ? Actually that >> is Valdis's way of motivating you. >> >> So good luck and we are here if you have questions :-) >> >> there is always the possibility of >>> something you didn't know about trashing your system. See >>> 5.12.0-rc1-dontuse >>> for a nasty bug with file-backed swap that would stomp all over a >>> section of your >>> filesystem, and there was an ext[34] (can't remember anymore) bug during >>> 2.5 >>> that would trash the filesystem when you *unmounted* it. So you could >>> boot the >>> new kernel for testing, shutdown and boot the older version, and find it >>> won't boot and be blaming the older version until we figured out what was >>> happening. :) >>> >>> But seriously - if you have a good backup of the system, and an bootable >>> external image that you can use for rescue, there's not much a kernel >>> screw-up >>> can do to permanently lose date. >>> >> >> Agreed 110%. >> >>> >>> Of course, WIndows Update is at that same level of reliability, so >>> "knowing how >>> to recover a trashed system" is an important skill no matter what OS you >>> run :) >>> >> >> Hope this helps - Aruna >> >

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Re: How to switch between installed kernel and developed kernel
by Valdis Klētnieks March 23, 2021

March 23, 2021

On Tue, 23 Mar 2021 16:37:13 +0200, you said: > I gave up for now and prepared bash script for removing the files, based on > the information in > https://www.cyberciti.biz/faq/debian-redhat-linux-delete-kernel-command/ > (see "A note about custom compiled Linux kernel" section). In my opinion, > if Makefile supports install, it should support uninstall as well. Well, here's the thing.. the just-built kernel tree know what it has to install because it was just built with that .config, and it knows what files it just built. But how is that 5.12-rc4 build supposed to know what to remove that belonged to a 5.9 kernel built with a different .config that the 5.12-rc4 used, and which potentially had more modules enabled than the current source tree? Bonus points for knowing how to figure out if the 5.9 kernel was installed via rpm or dpkg or opkg or 'make install', and whether the 'make install' invoked the system-supplied /sbin/installkernel script, or the user provided a variant that installed more/less/different files? Especially as you noted, that it's a 3 or 4 line bash script to remove the files. And you hopefully know what extra rpm/dkpg stuff you need to clean up....

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Mismatch between tcp_output.c and tcp_fastopen.c in net/ipv4
by Navin P March 23, 2021

March 23, 2021

Hi, I've a question regarding bytes_received and bytes_sent. https://elixir.bootlin.com/linux/latest/source/net/ipv4/tcp_output.c#L1385 In net/ipv4/tcp_output.c if (skb->len != tcp_header_size) { tcp_event_data_sent(tp, sk); tp->data_segs_out += tcp_skb_pcount(skb); tp->bytes_sent += skb->len - tcp_header_size; } https://elixir.bootlin.com/linux/latest/source/net/ipv4/tcp_fastopen.c#L220 In net/ipv4/tcp_fastopen.c /* u64_stats_update_begin(&tp->syncp) not needed here, * as we certainly are not changing upper 32bit value (0) */ tp->bytes_received = skb->len; Above we miss tcp_header_size. 1. Shouldn't bytes_received be skb->len - tcp_header_size for consistency ? I'm not sure if skb->len - tcp_header_size is correct . 2. Should it not be skb->len - tcp_header_size - ip_header_size - skb->mac_len ? Can you please clarify on these ? Regards, Navin

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kernel projects for students
by Muni Sekhar March 22, 2021

March 22, 2021

Hi all, What are some good Linux projects in kernel space for final year computer.science engineering students? Could someone help and share your ideas on this please. -- Thanks, Sekhar

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picking the first patch
by Harsha Vardhan March 22, 2021

March 22, 2021

Hello team , Sorry for a vague question. So far I have spent a lot of time dreaming to be a kernel hacker without doing much , but I realised its geting too late and now I want to pick my first patch to work, I have decided to address the TODO at drivers/staging/grebus/TODO : " * Make pwm.c use the struct pwm_ops::apply instead of ::config, ::set_polarity, 4 ::enable and ::disable." To make sure this is a first good patch , I verified that there is traction for this driver recently. But I am not sure, let's say I change the code , how to test it ? Any thoughts on whether I should just do a checkpatch.pl change as my first patch ? Thanks Vardhan

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question about ioport_map function
by ckim＠etri.re.kr March 22, 2021

March 22, 2021

Hello all >From what I understand, to map io ports to virtual memory, we should use request_region, ioport_map/unmap and ioread/write functions. These are for architectures having input, output machine instructions like x86, x86_64. And the return address of ioport_map is physical address. Is my understanding correct? Thanks! Chan Kim

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