August 2017 - kernelnewbies@kernelnewbies.org

Don't know where to start linux kernel programming
by SUNIL KHORWAL Aug. 25, 2017

Aug. 25, 2017

Hi, I'm new to linux kernel programming, I want to be a linux kernel hacker but i don't know where to start. Please help me. Thanks Sunil Khorwal

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Kdump not working on latest kernels (4.13.0-rc6) ?
by Ritesh Harjani Aug. 21, 2017

Aug. 21, 2017

Hello, I tried to check the kdump utility on the latest kernel (4.13-rc6) on ubuntu. But I could not get it working. Is this functionality broken ? $ kdump-config show DUMP_MODE: kdump USE_KDUMP: 1 KDUMP_SYSCTL: kernel.panic_on_oops=1 KDUMP_COREDIR: /var/crash crashkernel addr: 0x current state: Not ready to kdump kexec command: /sbin/kexec -p --command-line="BOOT_IMAGE=/vmlinuz-4.4.0-87-generic root=/dev/mapper/vg00-rootvol ro printk.time=1 nomodeset gfxpayload=text fb=false irqpoll maxcpus=1 nousb" --initrd=/boot/initrd.img-4.4.0-87-generic /boot/vmlinuz-4.4.0-87-generic When I tried kdump-config load. It started giving me below errors :- "Unknown type (Reserved) while parsing /sys/firmware/memmap/15/type. Please report this as bug. Using RANGE_RESERVED now." So based on this thread (https://lkml.org/lkml/2017/3/23/944) I made below change and tried again. $ git diff diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c index 532da61..851364a 100644 --- a/arch/x86/kernel/e820.c +++ b/arch/x86/kernel/e820.c @@ -982,7 +982,7 @@ static const char *__init e820_type_to_string(struct e820_entry *entry) case E820_TYPE_UNUSABLE: return "Unusable memory"; case E820_TYPE_PRAM: return "Persistent Memory (legacy)"; case E820_TYPE_PMEM: return "Persistent Memory"; - case E820_TYPE_RESERVED: return "Reserved"; + case E820_TYPE_RESERVED: return "reserved"; default: return "Unknown E820 type"; } } With above change, I see below problem :- $ sudo kdump-config load ELF core (kcore) parse failed Cannot load /boot/vmlinuz-4.13.0-rc6+ * failed to load kdump kernel Does anyone know what is this issue? Is this broken functionality on latest kernel. Is there a known fix. Or am I doing anything wrong ? PS: my default is 4.4 kernel. I installed 4.13-rc6 kernel on top of that. Regards Ritesh

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request_module with params
by Okash Khawaja Aug. 21, 2017

Aug. 21, 2017

Hi, Is there a way to load a kernel module from another module and pass parameters to it? Something like request_module("mymod param1=val1"); Thanks, Okash

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SIP conntrack helper
by sougol gheissi Aug. 20, 2017

Aug. 20, 2017

Hello all, I have read that helpers in conntrack would give us the opportunity to pars the packets up to application layer. I want to pars the SIP packet, so I decided to use the SIP conntrack helper;which is nf_conntrack_sip. Unlike the functionality the helper itself gives, I want to find the SIP messages of type MESSAGE and read the request line of the packet. SO I add the following code into the line 256. char sub[mlen+1]; memcpy(sub,&limit[0], mlen)) sub[mlen]='\0'; printk(KERN_ALERT "method is:[%s]", sub); But the problem is, nothing is being printed. My question is, Can I use nf_conntrack_sip for my purpose? and if yes, what is wrong with my code? Thanks in advance.

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Kernel Newbies India Page
by Jitendra Aug. 19, 2017

Aug. 19, 2017

Hi All, While going through kenernewbies I found the India community page is empty. Although we have small community in pune which do one meetup every month. https://ideas.reserved-bit.com/w/Category:KernelMeetup Can we get the access of edit this page and update our activity over there. --- Jitendra

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mapping perf sample events(PEBS) to kernel code
by Probir Roy Aug. 16, 2017

Aug. 16, 2017

Hi, I am sampling Linux kernel using perf's perf_event_open functionality. The instruction pointers(IP) associated with PEBS events(PERF_RECORD_MISC_KERNEL), cannot be mapped back to kernel source code using addr2line while events generated from user-space (PERF_RECORD_MISC_USER) can be mapped back to application code. I am using appropriate vmlinux for kernel code attribution. Samples collected from existing perf tool can attribute to the kernel code. addr2line also works for those samples collected using perf tool. My question is why samples collected using perf_event_open fails to attribute to kernel code. Do I need to prepare the samples otherwise for the attribution? Thanks, Probir

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Load partially USB composite device
by loïc tourlonias Aug. 9, 2017

Aug. 9, 2017

Hi everybody, In my project I have an USB composite device (a LTE modem) which use USB to communicate with the processor. This device has several interface to communicate but I do not use all of them. In particular, it loads cdc_ether device which I don't use and I have an undesired ethXX which interferes with a service in my system. To schematize, let's say my device is loaded on port 2 of usb1, I have the following USB topology: - 1-2:1.0: tty - 1-2:1.1: tty - 1-2:1.2: tty - 1-2:1.3: tty - 1-2:1.4: tty - 1-2:1.5: eth (not desired) Is there a way to prevent this specific ethXX to mount? I've already tried to create a udev rules, but I don't manage to stop the loading process. Here is a summary of my tries: 1/ I couldn't use the /sys/bus/usb1/.../1-2/activated file in my udev rule because it's an USB composite device and I want to use the tty interfaces but not the eth interface 2/ I have tried to stop the udev loading process, but setting MODALIAS environment variable to a NULL-string doesn(t do the trick and last-rule udev option has been removed in my udev version (1.8.2). 3/ I have tried to create a custom environment variable IGNORE_ETH and modify my last rule which run modprobe with the modalias variable. In the logs I see that modprobe isn't called by udev rules, but the cdc_ether device is loaded all the same. 4/ I have think of creating a stub cdc_ether driver and use the /etc/modprobe.d/my_file.conf to preempt the loading for my specific usb composite device but this solution is ugly and I'm not sure it will work. Any idea will be great. Best Regads Loic

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Kernel build warnings
by Amit Kumar Aug. 8, 2017

Aug. 8, 2017

Hi, When I compile arm64/defconfig kernel with W=1, build emits a lot of warnings. When patch is required to be "build clean" then why warnings are there? I want to understand. Thanks in advance. Regards, Amit Kumar

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v2.6.39 GPIO power off
by Hayward, Shaun Aug. 5, 2017

Aug. 5, 2017

Hi everyone, I'm having a bit of a odd question regarding an fix for an old, embedded MPC8308 PPC Linux system (Linux 2.6.39, and no scope to upgrade to a newer kernel). The board needs to change the state of a GPIO output pin on shutdown to turn off power. Up until now, the shutdown and poweroff commands have never worked and users have just hard powered off. This was "good enough" for years, but not any more! In newer versions, this looks like it would be simply a case of adding a gpio-poweroff node to the device tree, but in 2.6 there does not seem to be anything as straight forward on this older kernel. It looks like arch/powerpc/platforms/83xx/mpc830x_rdb.c defines the specific settings for this board, but I'm having trouble finding anything that looks like it would the "right place to start". Are any of you able to give me some pointers as to where to start digging for this one? Thank you for your time and help! Shaun

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[IO Scheduler] : Query regarding Multi-Queue Block IO Queuing
by Narendra Pal Singh Aug. 3, 2017

Aug. 3, 2017

Hello all, I have a Ubuntu server with bunch of SSD and HDD. i want to enable blk-mq for SSDs only, as for rotational disks blk-mq might give negative performance (Please correct me here if i required). Is it possible to enable blk-mq for selective disks ? -- Best Regards, Narendra Pal Singh

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