April 2017 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

DWM 157 D1 Dongle support
by Narasimha M April 26, 2017

April 26, 2017

Hi All, I am trying to support DMW 157 D1 dongle. I have the pid (7600) and vids (2001) for this dongle. Could someone share the messagecontent for usb_modeswitch to convert into modem. Thanks in advance. -- Narasimha

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Re: What is the fastest way to build and boot a kernel (Manoj)
by Wenwu Xu (许文武) April 26, 2017

April 26, 2017

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What is the fastest way to build and boot a kernel
by Code Soldier1 April 25, 2017

April 25, 2017

Hi, Can someone suggest what is the fastest way to build a minimal kernel and boot. For example if I am working on TCP and would like to make a small change and reboot, what is the fastest way, I rather not build the whole kernel. Thanks -- CS1

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Re: Kernel CPU Utilization
by Ozgur Karatas April 25, 2017

April 25, 2017

> 21.04.2017, 19:19, "Stephen Brennan" <stephen(a)brennan.io>: > Hello all, > Hello, > I was wondering if anyone had some information on how CPU time used by the > kernel is accounted for, e.g. in top or htop. I would imagine that kernel code > running in process code would be "billed" toward that process. What about kernel > worker threads (for example, work_structs queued for later)? > > My overall goal is that I'm doing some large-scale network emulation, and I want > to ensure that the kernel is not using too much CPU time, otherwise the CPU > overhead may be messing with the results. I written to the code for myself, you can use and develop this code (open source). https://github.com/mueddib/cpustat > Thanks, > Stephen Regards, Ozgur

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[Offtopic] Are these good coding rules for C?
by Anuz Pratap Singh Tomar April 22, 2017

April 22, 2017

Hi, I came across this paper http://spinroot.com/gerard/pdf/P10.pdf written by someone at JPL, NASA. Some of the rules stated in this paper are good rules about bound checking and keeping functions short makes sense, whereas some others about malloc and pointers seems less of rules, but believing that programs are unable to handle these tasks properly. I am not sure if Linux in areas which are safety critical and if so does that code follow similar rules? -- Thank you Warm Regards Anuz

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what is the mostly used automation test framework
by Muni Sekhar April 22, 2017

April 22, 2017

Hello all, Can someone suggest what is the mostly used automation test framework for testing the linux kernel mode drivers? -- Thanks, Sekhar

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Kernel CPU Utilization
by Stephen Brennan April 21, 2017

April 21, 2017

Hello all, I was wondering if anyone had some information on how CPU time used by the kernel is accounted for, e.g. in top or htop. I would imagine that kernel code running in process code would be "billed" toward that process. What about kernel worker threads (for example, work_structs queued for later)? My overall goal is that I'm doing some large-scale network emulation, and I want to ensure that the kernel is not using too much CPU time, otherwise the CPU overhead may be messing with the results. Thanks, Stephen

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How to make per process firewall ?
by Lev Olshvang April 20, 2017

April 20, 2017

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Write from mmapped buffer to O_DIRECT output file
by Mikhail Karpenko April 19, 2017

April 19, 2017

Hello, I have a devices which writes to a video buffer. This buffer is allocated in system memory using CMA and I want to implement streaming write from this buffer to a block device. My application opens video buffer with mmap and I would like to use O_DIRECT write to avoid page cache related overhead. Basically, the pseudo-code of the application looks like this: f_in = open("/dev/videobuf", O_RDONLY); f_mmap = mmap(0, BUFFER_SIZE, PROT_READ, MAP_SHARED, f_in, 0); f_out = open("/dev/sda", O_WRONLY | O_DIRECT); write(f_out, f_mmap, BLOCK_SIZE); where BLOCK_SIZE is sector aligned value. f_out is opened without any errors, but write results in EFAULT. I tried to track down this issue and it turned out that mmap implementation in video buffer's driver uses remap_pfn_range(), which sets VM_IO and VM_PFNMAP flags for VMA. The O_DIRECT path in block device drivers checks these flags and returns EFAULT. As far as I understand (from reading comments to VMA flags), O_DIRECT writes need to pin the memory pages, but VMA flags indicate the absence of "struct page" for underlying memory which causes an error. Am I right here? And the main question is how to correctly implement O_DIRECT write from mmapped buffer? I have video buffer driver sources and can modify it appropriately. Mikhail

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Patch Question
by Perry Hooker April 19, 2017

April 19, 2017

Hi everyone, I recently submitted a patch to the kernel mailing list: https://lkml.org/lkml/2017/3/21/712 I received some feedback on the patch. After a bit of polite back-and-forth, the respondent stopped replying when I asked for more information, and I haven't heard anything from the maintainers. Based on my analysis (contained in the thread), I still think the patch is correct & appropriate. What's the best way to determine if this is a good fix or not? How should I proceed if the patch is, in fact, a good fix? Best regards, Perry

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