August 2021 - kernelnewbies@kernelnewbies.org

VFS: Cannot open root device "(null)" or unknown-block(0, 0): error -2
by jim.cromie＠gmail.com Aug. 15, 2021

Aug. 15, 2021

Im trying to configure a minimal kernel, that will work on a virtme / qemu / kvm stack I did make allnoconfig virtme-configkernel --update then I added BTRFS_FS, since thats the host fs. of course it didnt work. then tried DM, needed MD, added both, again didnt help. so I need to stop just guessing. (admittedly, asking is worse ?) heres how it actually goes: 9pnet: Installing 9P2000 support sched_clock: Marking stable (3466602654, 29303733)->(4050551166, -554644779) Btrfs loaded, crc32c=crc32c-generic, zoned=no 9pnet_virtio: no channels available for device /dev/root VFS: Cannot open root device "(null)" or unknown-block(0,0): error -2 Please append a correct "root=" boot option; here are the available partitions: Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) CPU: 0 PID: 1 Comm: swapper Tainted: G W 5.14.0-rc4+ #5 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014 Call Trace: dump_stack+0x1b/0x1d panic+0x95/0x202 mount_block_root+0x204/0x268 mount_root+0x5d/0x62 Heres a working kernel (if overlarge config) It has btrfs, md, which is why I took those guesses above zswap: loaded using pool lzo/zbud Key type ._fscrypt registered Key type .fscrypt registered Key type fscrypt-provisioning registered Btrfs loaded, crc32c=crc32c-generic, zoned=yes Key type encrypted registered PM: Magic number: 1:872:1009 RAS: Correctable Errors collector initialized. md: Skipping autodetection of RAID arrays. (raid=autodetect will force) qemu-system-x86_64: warning: 9p: degraded performance: a reasonable high msize should be chosen on client/guest side (chosen msize is <= 8192). See https://wiki.qemu.org/Documentation/9psetup#msize for details. VFS: Mounted root (9p filesystem) readonly on device 0:20. devtmpfs: mounted Freeing unused decrypted memory: 2036K Anybody see any clues ?

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My effort to learn Linux kernel development
by Amit Kumar Aug. 15, 2021

Aug. 15, 2021

Hi All, I am just here to inform that I am trying to learn Linux kernel development. If someone wants to follow me, so that he may also learn with me. https://freeark1blog.blogspot.com/2021/07/my-aspiration-go-live.html https://freeark1blog.blogspot.com/2021/07/the-minimal-c-program.html https://twitter.com/freeark1 I'll send update on this mail thread. Please, stay tuned. Regards, Amit Kumar

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Linux Kernel build dpkg-buildpackage error
by Adverg Ebashinskii Aug. 15, 2021

Aug. 15, 2021

Hello! I’m trying to build Linux Kernel from upstream and faced some build error. Environment: Ubuntu 20.04 gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0 Linux Kernel 5.8.0-59-generic Steps to build: I follow the instructions specified in this site https://wiki.ubuntu.com/KernelTeam/GitKernelBuild 1 cp /boot/config-$(uname -r) .config 2 make olddefconfig 3 make clean 4 make -j $(getconf _NPROCESSORS_ONLN) deb-pkg LOCALVERSION=-custom After pretty long time of compiling source files I got the following error: make[2]: *** [debian/rules:7: build-arch] Error 2 dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2 make[1]: *** [scripts/Makefile.package:77: deb-pkg] Error 2 make: *** [Makefile:1559: deb-pkg] Error 2 Is there a way to fix that? -- Regards, Adverg Ebashinskii

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None
by Adverg Ebashinskii Aug. 15, 2021

Aug. 15, 2021

Hello! I’m trying to build Linux Kernel from upstream and faced some build error. Environment: Ubuntu 20.04 gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0 Linux Kernel 5.8.0-59-generic Steps to build: I follow the instructions specified in this site https://wiki.ubuntu.com/KernelTeam/GitKernelBuild 1 cp /boot/config-$(uname -r) .config 2 make olddefconfig 3 make clean 4 make -j $(getconf _NPROCESSORS_ONLN) deb-pkg LOCALVERSION=-custom After pretty long time of compiling source files I got the following error: make[2]: *** [debian/rules:7: build-arch] Error 2 dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2 make[1]: *** [scripts/Makefile.package:77: deb-pkg] Error 2 make: *** [Makefile:1559: deb-pkg] Error 2 Is there a way to fix that? -- Regards, Adverg Ebashinskii

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Re: USB-Audio: Device or resource busy (strace log)
by Muni Sekhar Aug. 13, 2021

Aug. 13, 2021

On Wed, Aug 11, 2021 at 6:19 PM vishnu <vardhanraj4143(a)gmail.com> wrote: > > can you paste output of > arecord -l (list of capture devices). $ arecord -l **** List of CAPTURE Hardware Devices **** card 0: USB [Plantronics .Audio 628 USB], device 0: USB Audio [USB Audio] Subdevices: 1/1 Subdevice #0: subdevice #0 > Which device you are using and os. > Does this instance is already open by default? like any video playing or something like that? lsof does not catch it. > > Yes you can stop pulse audio and try.. > > On Wed, Aug 11, 2021 at 6:17 PM Jaroslav Kysela <perex(a)perex.cz> wrote: >> >> On 11. 08. 21 14:36, Muni Sekhar wrote: >> > Hi All, >> > >> > $ cat /proc/asound/cards >> > 0 [USB ]: USB-Audio - Plantronics .Audio 628 USB >> > Plantronics Plantronics .Audio 628 USB at >> > usb-0000:00:14.0-2, full speed >> > >> > I am using a Plantronics USB Audio headset. >> > >> > $ arecord --device hw:0,0 --channels 2 --format S16_LE --rate 44100Hz x.wav >> > arecord: main:722: audio open error: Device or resource busy >> > >> > >> > 'arecord' command always fails the first time after system boot in my >> > system. But subsequent execution of the 'arecord' command runs fine. >> > >> > >> > I've attached the strace log for the "audio open error: Device or >> > resource busy" failure. Is there any fix available for this issue? >> >> You may check which other task blocks the PCM device: >> >> lsof /dev/snd/pcmC0D0c It does not output any process. $ lsof /dev/snd/pcmC0D0c 1st run: ---------- $ arecord --device hw:0,0 --channels 2 --format S16_LE --rate 44100Hz x.wav arecord: main:722: audio open error: Device or resource busy 2nd run: ---------- $ arecord --device hw:0,0 --channels 2 --format S16_LE --rate 44100Hz x.wav Recording WAVE 'x.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo ^CAborted by signal Interrupt... >> >> I guess that it will be pulseaudio (device enumeration). >> >> Jaroslav >> >> -- >> Jaroslav Kysela <perex(a)perex.cz> >> Linux Sound Maintainer; ALSA Project; Red Hat, Inc. -- Thanks, Sekhar

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Re: LDD 3rd ed. - It was: Re: read() via USB bus
by Greg KH Aug. 12, 2021

Aug. 12, 2021

On Thu, Aug 12, 2021 at 11:45:45AM +0200, Fabio M. De Francesco wrote: > Hi Greg, > > On Monday, August 9, 2021 10:44:23 AM CEST Greg KH wrote: > > On Mon, Aug 09, 2021 at 10:15:29AM +0200, Oliver Neukum wrote: > > > On 09.08.21 09:58, Muni Sekhar wrote: > > > > Hi all, > > > > > > > > PCIe memory mapped registers can be read via readb(), readw(), readl() > > > > kernel API's. Similarly what are the kernel API to read the device > > > > registers via USB bus > > > > > > [...] > > > > > > I hope this list stays friendly to newcomers and we will answer > > > specific questions, but at this point I must advise you to first > > > read an introductory book. > > > > Along these lines, take a look at the book, Linux Device Drivers, third > > edition, which is free online, as it has a chapter about USB drivers and > > how they work. That should help you out to understand the issues > > involved with USB devices. > > > I've heard that your book, LDD 3rd edition, has become obsolete a long time > ago and most sample code cannot anymore build. Reading what you wrote above > seems to contradict what I've been told by others... I must admit that I've > just had a print copy of it that I have not yet opened for reading, therefore > maybe that I'm totally wrong in assuming the above. Look into it and see the differences, it's not hard to notice. And the code samples are all up to date online on github somewhere, there's people keeping them alive if you want to track them down, but really, just look at the in-kernel drivers for better examples of real drivers. > Do you mind to elaborate a bit more on this subject, please? I mean: can you > point out which chapters, which content, should be skipped (if there's really > something which is no more correct/relevant to today's practice of drivers > development and kernel hacking? I am not going to create a study guide like this, sorry, I've already given away the book for free to you :) > One more question, please... if after carefully studying its content, someone > wanted to change and update part of the book content to reflect the changes in > Linux API and in the current best practices, would it be (legally) allowed to > publish a v4 on GitHub for the convenience of everyone interested in learning > for free? However, I understand that it would be not so easy to come up with a > good and error free text if not addressed as a public long term project and > I'm also not sure of what tools are needed to edit PDF files. (At the moment > my question is for a hypothetical scenario, just to know whether or not it > would be technically and legally doable). Please see the license of the book for what you are, and are not, allowed to do with it to answer this question. thanks, greg k-h

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Re: LDD 3rd ed. - It was: Re: read() via USB bus
by Valdis Klētnieks Aug. 12, 2021

Aug. 12, 2021

On Thu, 12 Aug 2021 11:45:45 +0200, "Fabio M. De Francesco" said: > I've heard that your book, LDD 3rd edition, has become obsolete a long time > ago and most sample code cannot anymore build. Reading what you wrote above > seems to contradict what I've been told by others... I must admit that I've > just had a print copy of it that I have not yet opened for reading, therefore > maybe that I'm totally wrong in assuming the above. The APIs have all changed a lot since the 3rd edition. The concepts haven't changed that much. And given that the in-kernel APIs have *always* been a moving target, being able to deal with the fact that a given function now takes a 'struct foo*' rather than a 'struct bar *' is a very necessary skill for anybody who's planning to do serious kernel work.

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A question about staging driver like pi433
by Sidong Yang Aug. 12, 2021

Aug. 12, 2021

Hi all, I have a question about staging driver. I'm a newbie kernel developer and I tried contributed some patches for staging drivers. In those staging drivers, I'm interested in pi433 and wrote some patches for it about 2 years ago. and then I tried to go deeper for that. I tried to buy pi433 device but I can't. It seems that no longer available. In this case, pi433 should be removed from source tree? If not, It's okay to send patches for it? Thanks, Sidong

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Re: USB-Audio: Device or resource busy (strace log)
by Jaroslav Kysela Aug. 11, 2021

Aug. 11, 2021

On 11. 08. 21 14:36, Muni Sekhar wrote: > Hi All, > > $ cat /proc/asound/cards > 0 [USB ]: USB-Audio - Plantronics .Audio 628 USB > Plantronics Plantronics .Audio 628 USB at > usb-0000:00:14.0-2, full speed > > I am using a Plantronics USB Audio headset. > > $ arecord --device hw:0,0 --channels 2 --format S16_LE --rate 44100Hz x.wav > arecord: main:722: audio open error: Device or resource busy > > > 'arecord' command always fails the first time after system boot in my > system. But subsequent execution of the 'arecord' command runs fine. > > > I've attached the strace log for the "audio open error: Device or > resource busy" failure. Is there any fix available for this issue? You may check which other task blocks the PCM device: lsof /dev/snd/pcmC0D0c I guess that it will be pulseaudio (device enumeration). Jaroslav -- Jaroslav Kysela <perex(a)perex.cz> Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

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Re: USB-Audio: Device or resource busy (strace log)
by vishnu Aug. 11, 2021

Aug. 11, 2021

can you paste output of arecord -l (list of capture devices). Which device you are using and os. Does this instance is already open by default? like any video playing or something like that? On Wed, Aug 11, 2021 at 6:06 PM Muni Sekhar <munisekharrms(a)gmail.com> wrote: > Hi All, > > $ cat /proc/asound/cards > 0 [USB ]: USB-Audio - Plantronics .Audio 628 USB > Plantronics Plantronics .Audio 628 USB at > usb-0000:00:14.0-2, full speed > > I am using a Plantronics USB Audio headset. > > $ arecord --device hw:0,0 --channels 2 --format S16_LE --rate 44100Hz x.wav > arecord: main:722: audio open error: Device or resource busy > > > 'arecord' command always fails the first time after system boot in my > system. But subsequent execution of the 'arecord' command runs fine. > > > I've attached the strace log for the "audio open error: Device or > resource busy" failure. Is there any fix available for this issue? > > -- > Thanks, > Sekhar >

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