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ssh session with qemu-arm using busybox
by Pintu Agarwal March 12, 2019

March 12, 2019

Hi, I have a qemu-arm setup with busybox which I normally use to test my kernel changes. I use this command to boot it: QEMU-ARM$ qemu-system-arm -M vexpress-a9 -m 1024M -kernel ../KERNEL/linux/arch/arm/boot/zImage -dtb ../KERNEL/linux/arch/arm/boot/dts/vexpress-v2p-ca9.dtb -initrd rootfs.img.gz -append "console=ttyAMA0 root=/dev/ram rdinit=/sbin/init ip=dhcp" -nographic -smp 4 This includes, my own custom kernel and rootfs build. For rootfs I use busybox and create cpio image and use it as initrd. But, every time, if I have to copy some files inside qemu, I need to create create roofs image. This is painful. So, now I am exploring how to transfer files from my ubuntu pc to qemu-session using "ssh". I know this is possible, but I am still not successful, and bit lazy to explore these. I am sure, many of you people would have explored already "how to use ssh over qemu" and found a easy method. So, if anybody have easy setup please share with me. I could see that after adding "ip=dhcp" I get the eth0 interface like this: / # ifconfig eth0 Link encap:Ethernet HWaddr 52:54:00:12:34:56 inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:2 errors:0 dropped:0 overruns:0 frame:0 TX packets:2 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:1180 (1.1 KiB) TX bytes:1180 (1.1 KiB) Interrupt:22 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:65536 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) But I could not ping it from ubuntu PC. Regards, Pintu

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I2C drivers for Snapdragon 820
by Shahid Ali Nadaf March 12, 2019

March 12, 2019

Hi all, I am new to Linux kernel. I have developed basic drivers on micro-controllers and now i want to dive deep into the Linux world. I have a snapdragon 820 development board running Android 7.1.1, Kernel version 3.18.31. I have a RF card which i need to interface with Snapdragon 820 development board over I2C. Can someone guide how to go about it??? Can someone share a document which explains the I2C driver implementation on Linux. Any help would be appreciated............!!!!!! Thanks, Shahid

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I2C drivers for Snapdragon 820
by Shahid Ali Nadaf March 12, 2019

March 12, 2019

Hi all, I am new to Linux kernel. I have developed basic drivers on micro-controllers and now i want to dive deep into the Linux world. I have a snapdragon 820 development board running Android 7.1.1, Kernel version 3.18.31. I have a RF card which i need to interface with Snapdragon 820 development board over I2C. Can someone guide how to go about it??? Can someone share a document which explains the I2C driver implementation on Linux. Any help would be appreciated............!!!!!! Thanks, Shahid

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What will happen on attempt to write to read-only page when CONFIG_MEM_SOFT_DIRTY is off ?
by Lev Olshvang March 11, 2019

March 11, 2019

Hello all, Please help me to clarify what will page fault handler do (if any) File arch/x86/include/asm/pgtable_types.h have following comment for 2 PAGE_DIRTY_BITs #define _PAGE_BIT_DIRTY 6 /* was written to (raised by CPU) */ _PAGE_BIT_SOFT_DIRTY _PAGE_BIT_SOFTW3 /* software dirty tracking */ While documentation clearly explains that Page Fault handler sets second flag https://www.kernel.org/doc/Documentation/vm/soft-dirty.txt I do not have idea what will happen when tracking Soft Dirty flags is off, I suppose the answer is in mm/gup.c but I was not able to track it to page handler. Thanks you all. Lev.

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Finding all modules which consume kernel lib?
by Andy Nicholas March 9, 2019

March 9, 2019

Hello, Is there a website or service or tool or package or script or something which allows me to determine which pieces of the compiled kernel (especially modules) contained the source-code changes I might make to any given directory? Like a kernel-code dependency graph website? For instance, assume I made a change to code in net/wireless/. How do I figure out which pieces of the kernel or modules get linked against the library built from this directory? I could attempt to trace the kernel's build output line-by-line and then grep through the output looking for which other code is linking against cfg80211. That is way too tedious. In this case I would like to know which kernel modules I would need to, potentially, re-test because I apply a patch to this directory.... without examining the build logs. In my case I'm applying some patches and I'd like to make sure I am installing and testing the correct set of related atheros modules. Thank you, andy

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How to avoid or reduce GFP_ATOMIC allocation failed
by wuzhouhui March 8, 2019

March 8, 2019

Hi, I check kernel code and found that GFP_ATOMIC allocation will use emergency pool and maybe failed if emergency pool is not enough. And GFP_ATOMIC doesn't trigger reclaim (because of ATOMIC) even if there are a lot of page caches. So my question is how to avoid or reduce GFP_ATOMIC allocation failed if there are enough reclaimable memory? Is there some kernel parameters can be configured? Thanks.

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exit-code of 251
by prashantkumar dhotre March 7, 2019

March 7, 2019

Hi, Could you please let me know if any system call can exit with 251 ? I am trying to find out who exited with 251 ? Thanks On Mon, Mar 4, 2019 at 9:09 PM Norbert Kalmar <nkalmar(a)cloudera.com.invalid> wrote: > Hi Prashant, > > Depending on your version, exit codes are static variables in ExitCode.java > But we do not use 251, we only go as far as 14 with exit codes. This looks > like an app specific exit code. > Are you using some kind of systemd script to start ZooKeeper? > > Regards, > Norbert > > On Mon, Mar 4, 2019 at 12:49 PM prashantkumar dhotre < > prashantkumardhotre(a)gmail.com> wrote: > > > Hi, > > > > In my journal log, I see ; > > > > 1199473 Mar 01 15:46:03 evo-qfx-01 systemd[1]: ifmand.service: Main > process > > exited, code=exited, status=251/n/a > > > > In my app, I don't explicitly call exit(251). > > I use zookeeper lib. > > Fro my logs,I see that after a call to zookeeper lib API > zookeeper_close() > > , I see that my service exited with 251. > > Is 251 a std exit code or app/lib specific custom exit code ? > > I want to know what does 251 means. > > > > Can you please let me know where can I see the exit-code to meaning > > mapping > > ? > > > > Thanks > > > > Prashant > >

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Using EHSET module
by CHMIELARZ Radoslaw March 7, 2019

March 7, 2019

Hi, I'm trying to certify USB on our device that is running Linux 4.14. For windows systems we were using https://www.usb.org/usb2tools. For linux the only option I have found is a kernel module called EHSET. Unfortunately I can't manage to get it working, can You please help? I have added the following configuration: * CONFIG_USB_HCD_TEST_MODE=y * USB_EHSET_TEST_FIXTURE=m Then on the system I type in modprobe ehset. After this looking at the source code of ehset.c<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/dri…> I assumed that inserting USB stick with VendorID: 0x1a0a and ProductID: 0x0104 would start the Packet command, but it doesn't do anything (not output visible on the oscilloscope). The device is loaded as a regular USB stick. The output I see is: [ 1059.904034] ci_hdrc ci_hdrc.0: new USB bus registered, assigned bus number 1 [ 1059.935515] ci_hdrc ci_hdrc.0: USB 2.0 started, EHCI 1.00 [ 1059.941700] usb usb1: New USB device found, idVendor=1d6b, idProduct=0002 [ 1059.948523] usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber=1 [ 1059.955776] usb usb1: Product: EHCI Host Controller [ 1059.960680] usb usb1: Manufacturer: Linux 4.14.87-rt50 ehci_hcd [ 1059.966627] usb usb1: SerialNumber: ci_hdrc.0 [ 1059.974486] usb usb1: usb_probe_device [ 1059.982387] hub 1-0:1.0: usb_probe_interface [ 1059.986735] hub 1-0:1.0: USB hub found [ 1059.990614] hub 1-0:1.0: 1 port detected [ 1060.475521] usb 1-1: new high-speed USB device number 2 using ci_hdrc [ 1060.677970] usb 1-1: New USB device found, idVendor=1a0a, idProduct=0104 [ 1060.684709] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [ 1060.691877] usb 1-1: Product: USB DISK 3.0 [ 1060.696005] usb 1-1: Manufacturer: [ 1060.700215] usb 1-1: SerialNumber: 190073AE389B2300 [ 1060.708279] usb 1-1: usb_probe_device [ 1060.716351] usb-storage 1-1:1.0: usb_probe_interface [ 1060.724692] usb-storage 1-1:1.0: USB Mass Storage device detected [ 1060.745330] scsi host1: usb-storage 1-1:1.0 Thanks in advance! Radek

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CMA allocation failure
by Pankaj Suryawanshi March 7, 2019

March 7, 2019

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undefined reference to `ioctl_tty'
by Jeffrey Walton March 7, 2019

March 7, 2019

Hi Everyone, I'm working from http://man7.org/linux/man-pages/man4/tty_ioctl.4.html . According to the man page: TIOCEXCL void Put the terminal into exclusive mode. No further open(2) operations on the terminal are permitted. (They fail with EBUSY, except for a process with the CAP_SYS_ADMIN capability.) The page goes on to say in the colophon it is part of the 4.16 kernel. I am running on the 4.20 kernel: $ uname -a Linux silo 4.20.13-200.fc29.x86_64 #1 ... GNU/Linux However: gcc -D_GNU_SOURCE -g2 -std=gnu99 test.c -o tttt -lrt test.c: In function ‘main’: test.c:11:7: warning: implicit declaration of function ‘ioctl_tty’; did you mean ‘ioctl’? [-Wimplicit-function-declaration] if (ioctl_tty(1 /*STDOUT_FILENO*/, TIOCEXCL, NULL) == -1) { ^~~~~~~~~ ioctl /usr/bin/ld: /tmp/ccCNNyG3.o: in function `main': /home/test/test.c:11: undefined reference to `ioctl_tty' collect2: error: ld returned 1 exit status Search is producing a lot of non-relevant hits. Any ideas why I can't find ioctl_tty during link when using a 4.20 kernel? Thanks in advance. ---------- $ cat test.c #include <stdio.h> #include <string.h> #include <errno.h> #include <termios.h> #include <fcntl.h> #include <sys/ioctl.h> int main(int argc, char* argv[]) { if (ioctl_tty(1 /*STDOUT_FILENO*/, TIOCEXCL, NULL) == -1) { fprintf(stderr, "%s\n", strerror(errno)); return 1; } return 0; }

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