November 2014 - kernelnewbies@kernelnewbies.org

How to handle Hotplug with UIO userspace driver
by Mandeep Sandhu Sept. 28, 2017

Sept. 28, 2017

Hi All, We're working on a custom PCIe based hardware, which can be hotplugged into the system. We're using the UIO approach of having a minimal kernel driver which basically handles the interrupt and provides a mmap of the device memory to userspace and userspace driver which mmap's the provided memory and manages the device. We're using systemd and udev rules to spawn off a user process whenever the hardware is plugged into the system. Now my question is, how can we gracefully inform the userspace process if someone pulls out the hardware (sitting on a PCI slot). Even with full hotplug support, there can always be a case of "surprise removal", where someone yanks the board without going through the whole "attention button" routine. While the kernel driver has no problem with hot-removal, I see that if I "unregister" our UIO driver in response to the removal, then the mapping for the hardware's physical memory would become "invalid" (done by UIO on unregsiter). This could possibly cause the user-space process to crash due to illegal memory access. Is there a "standard" way to handle this scenario, i.e for hotpluggable hardware using UIO? Basically, we'd want to "unregister" the UIO device only after the userspace process is informed of the removal so that it could unmap/close the device and exit gracefully. We could try doing it using some systemd trick, where we put a dependency on one of the UIO created files (/dev/uioX), so that when the file is destroyed, systemd could kill/shutdown the process. Although, there's no guarantee that the userspace process won't try to access the mmaped space during that interval, so this isn't a reliable solution either. Any hints, thoughts? Thanks., -mandeep

3 7

How to get the inode - no path_lookup
by Rishi Agrawal Sept. 17, 2015

Sept. 17, 2015

Hi All, I had a module which used the path_lookup function to print the details of any file's inode. I now want to rewrite that module in order to show some juniors how to write some code in kernel. I am using 3.4.6 kernel, I tried finding out path_lookup but google showed that it has been removed. I tried the following code then which did not work . . . dentry = kern_path_create(AT_FDCWD, filename, &path, 1); if (IS_ERR(dentry)) { printk("Failed to obtain the dentry"); return; } its not returning dentry I again tried after seeing the implementation of vfs_stat function user_path_at(AT_FDCWD, filename, lookup_flags, &path); but this also fails. I am using a proc interface to pass the filename, and copying the filename into a kernel buffer. How can I get a copy of vfs inode for a file name. -- Regards, Rishi Agrawal

4 8

Looking for ARM SoC porting guidelines
by Mike Thompson Feb. 2, 2015

Feb. 2, 2015

I'm working on a port the latest Linux kernel to a Nuvoton N32905 - a very inexpensive ARM9 based SoC similar to the Freescale iMX23 in many respects. My hope is that my code for this SoC will eventually reach the mainline kernel, but the whole process a fairly daunting task to a kernel newbie such as myself. I do have a six year old port of the 2.6.35 kernel to this SoC to help as a reference, but it's pretty much a rewrite to support devicetree, the common clock framework, and a myriad of changes needed to get a new SoC supported in the mainline kernel. Not to mention all the 2.6.35 code added for this chip isn't even close to the coding standards for the Kernel. So far I got the 3.17 kernel running pretty well the baseline peripherals such as clocks, interrupt controller, UART, GPIO & pin muxing along with hire level peripherals such as MMC/SD card support, MTD NAND and NOR flash and USB host support. As a guide, I've been using other ARM SoCs for examples and a number of very useful presentations on ARM SoC support from the Free Electron folks. Although presentations such as the "ARM SoC Linux Support Check-list" are very useful, they don't go into much detail. My question is two fold. Is there detailed information of all the things that need to be covered in the code to introduce a new ARM SoC into the kernel? Then, is there a description of how I start to go about contributing support for this chip into the Linux kernel? I honestly don't really know where to begin. Any advice or pointers would be sincerely appreciated. Mike Thompson BTW, my git reposity for this SoC is: https://github.com/mpthompson/linux/tree/n329

3 7

Problem facing while running checkpatch.pl on linux-next tree
by Rahul Garg Dec. 25, 2014

Dec. 25, 2014

Hi All, I am trying to run checkpatch.pl on linux-next tree's staging folder. But whatever sub directory, I try to run it on. It is giving me the same error for all the files : ERROR: Does not appear to be a unified-diff format patch I thought that it might be a problem with my git. So I clone the git tree again. So can anyone help me, what am I missing ? Regards Rahul

5 4

How to submit for eudyptula-challenge
by wangyubin Dec. 19, 2014

Dec. 19, 2014

Hello, I have dive into the eudyptula-challenge, but when I submit my result for task 01. I received a reply below: > Please print to the kernel debug log level. I have sended module(c file), Makefile, and dmesg output for load/unload the module. Could anyone to tell me what does this message mean? Thanks a lot! -- Best Regards! wangyubin

15 20

[eudyptula] has anyone received a gift after completing the challenge ?
by Denis Pithon Dec. 16, 2014

Dec. 16, 2014

Hi all, I have finished the challenge some month ago and wonder if somebody has received something from the Linux Foundation ? :-) Thanks Denis

12 14

[Eudyptula] How long have you been waiting?
by karthik nayak Dec. 5, 2014

Dec. 5, 2014

Hello, As patient as I am, just wondering how long have you all been waiting for your response. I'm waiting for quite a while now on the 8th task. Regards, Karthik Nayak

6 10

The limit of kernel memory in 64bit system
by J.Hwan Kim Dec. 1, 2014

Dec. 1, 2014

Hi, everyone As far as I know, the kernel memory limit is 1GB in 32bit system. Is it also applicable to 64bit system? What's the limit of kernel memory in 64bit system? Thanks in advance Regards, J.Hwan Kim

5 5

Query on USB related debugging
by Victor Ascroft Nov. 30, 2014

Nov. 30, 2014

Hello, I have an embedded device with a Freescale ARM Cortex A5 processor, running the 3.18-rc5 kernel. I have a problem where using the Ethernet over USB client stops functioning after a while. If I set the IP of the usb0 interface and try to ping the device from the host or vice versa, it works fine up to that point. Running iperf, establishes a connection to the host, but, doesn't complete even one cycle. Checking /proc/interrupts shows that after a while, probably a few seconds, it freezes. No more interrupts are serviced it seems. I put in a few debug prints in udc_irq to check, if things go right superficially at least, udc_irq seems to exit cleanly and of course my device doesn't hang. root:~# cat /proc/interrupts CPU0 27: 15122 GIC 27 gt 107: 162 GIC 107 40034000.usb The above number of interrupts does not increase at some point, showing that irq's are not serviced any more. My main query is how can I go about and start debugging this issue? What process, tools or methods I can use to debug and solve this problem. I have done some debugging before in the kernel/u-boot, but, the problems have always been which lead to crashes. So, the origin of it was at least clear, if not the source/cause of it. In this scenario, I am at a loss in which direction to start digging. I enabled prints for the whole USB driver section, with dynamic debug, but, this doesn't help much or at least I am not able to make out much from it. Below is the relevant dmesg log. [ 1.175253] using random self ethernet address [ 1.182722] using random host ethernet address [ 1.205327] using random self ethernet address [ 1.212857] using random host ethernet address [ 1.220419] g_ether gadget: adding config #2 'RNDIS'/808055c8 [ 1.220467] g_ether gadget: adding 'rndis'/8ea48300 to config 'RNDIS'/808055c8 [ 1.220545] g_ether gadget: RNDIS: dual speed IN/ep1in OUT/ep1out NOTIFY/ep2in [ 1.220566] g_ether gadget: cfg 2/808055c8 speeds: high full [ 1.220583] g_ether gadget: interface 0 = rndis/8ea48300 [ 1.220599] g_ether gadget: interface 1 = rndis/8ea48300 [ 1.220617] g_ether gadget: adding config #1 'CDC Ethernet (ECM)'/8080551c [ 1.220646] g_ether gadget: adding 'cdc_ethernet'/8ea483c0 to config 'CDC Ethernet (ECM)'/8080551c [ 1.220701] g_ether gadget: CDC Ethernet: dual speed IN/ep1in OUT/ep1out NOTIFY/ep2in [ 1.220721] g_ether gadget: cfg 1/8080551c speeds: high full [ 1.220737] g_ether gadget: interface 0 = cdc_ethernet/8ea483c0 [ 1.220753] g_ether gadget: interface 1 = cdc_ethernet/8ea483c0 [ 1.220778] g_ether gadget: Ethernet Gadget, version: Memorial Day 2008 [ 1.230557] g_ether gadget: g_ether ready [ 1.682860] g_ether gadget: high-speed config #1: CDC Ethernet (ECM) [ 1.692933] g_ether gadget: init ecm [ 1.692957] g_ether gadget: notify connect false [ 1.702757] g_ether gadget: activate ecm [ 1.702798] g_ether gadget: ecm_close [ 1.710720] g_ether gadget: packet filter 0e [ 1.710734] g_ether gadget: ecm req21.43 v000e i0000 l0 [ 1.786925] g_ether gadget: packet filter 0e [ 1.786946] g_ether gadget: ecm req21.43 v000e i0000 l0 [ 1.789824] g_ether gadget: packet filter 0e [ 1.789843] g_ether gadget: ecm req21.43 v000e i0000 l0 [ 1.790733] g_ether gadget: setup complete --> -108, 0/0 [ 1.790750] g_ether gadget: packet filter 0e [ 1.790768] g_ether gadget: ecm req21.43 v000e i0000 l0 [ 1.806118] g_ether gadget: notify connect false [ 1.838131] g_ether gadget: notify speed 425984000 [ 6.277081] g_ether gadget: packet filter 0e [ 6.277103] g_ether gadget: ecm req21.43 v000e i0000 l0 [ 294.926900] [472] usb_f_ecm:ecm_open:665: g_ether gadget: ecm_open [ 294.926930] [472] usb_f_ecm:ecm_do_notify:405: g_ether gadget: notify connect true [ 294.945515] <intr> usb_f_ecm:ecm_do_notify:420: g_ether gadget: notify speed 425984000 [ 294.948877] <intr> usb_f_ecm:ecm_setup:490: g_ether gadget: packet filter 0e [ 294.948904] <intr> usb_f_ecm:ecm_setup:519: g_ether gadget: ecm req21.43 v000e i0000 l0 [ 295.009820] <intr> usb_f_ecm:ecm_setup:490: g_ether gadget: packet filter 0e [ 295.009846] <intr> usb_f_ecm:ecm_setup:519: g_ether gadget: ecm req21.43 v000e i0000 l0 [ 324.637471] <intr> usb_f_ecm:ecm_setup:490: g_ether gadget: packet filter 0e [ 324.637500] <intr> usb_f_ecm:ecm_setup:519: g_ether gadget: ecm req21.43 v000e i0000 l0 Any pointers would be useful. Thanks! --Regards.

2 1

Error in compiling Linux kernel after creating hello world system call
by Jackson Isaac Nov. 29, 2014

Nov. 29, 2014

Hi everyone, I am trying to write hello world system call in linux but I am encountering the following error when I run 'sudo make': ... AR arch/x86/lib/lib.a LINK vmlinux LD vmlinux.o ld: cannot find hello: File format not recognized make: *** [vmlinux] Error 1 I have Linux 3.15.6 in my home directory and have created a hello folder in it. I also made changes to makefile, syscalls.h, and syscall_64.tbl in make file I replaced core-y += kernel/ mm/ fs/ ipc/ security/ crypto/ block/ with core-y += kernel/ mm/ fs/ ipc/ security/ crypto/ block/ hello Can anyone point out where I am going wrong. I have made the changes first and then I am trying 'sudo make'. I tried making some minor modifications and running it again 3 4 times but getting the same error and also it takes 2-3 hours of time. Jackson Isaac S5 B.Tech CSE Amrita Vishwa Vidyapeetham Jackson Isaac's Blog Github/JacksonIsaac

3 2