August 2014 - kernelnewbies@kernelnewbies.org

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

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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

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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

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Re: [PATCH] reformat_with_checkpatch: Add automation to checkpatch
by Greg KH Oct. 30, 2014

Oct. 30, 2014

On Fri, Jul 11, 2014 at 06:46:52PM -0700, Joe Perches wrote: > On Fri, 2014-07-11 at 18:39 -0700, Greg KH wrote: > > On Fri, Jul 11, 2014 at 06:21:27PM -0700, Joe Perches wrote: > > > A simple script to run checkpatch --fix for various types of > > > of cleanups. > ] > > drivers/staging/lustre/include/linux/lnet/api.h has no obvious style problems and is ready for submission. > > file: <drivers/staging/lustre/include/linux/lnet/api.h> description: <update c90 comment style> types:<c99_comments> > > Useless use of greediness modifier '+' in regex; marked by <-- HERE in m/(^\+.*) {8,8}+ <-- HERE \t/ at ./scripts/checkpatch.pl line 2217. > [] > > drivers/staging/lustre/include/linux/lnet/api.h has no obvious style problems and is ready for submission. > [] > > Is that expected? > > No, I haven't seen that. > > Can you tell me what git tree you're working on? My staging-next branch of staging.git on git.kernel.org > Also, can you use the scripts/checkpatch from -next > tag next-20140711 that will take a bit to checkout, I'll do that afterward. > My system has: > > $ perl --version > > This is perl 5, version 18, subversion 2 (v5.18.2) built for i686-linux-gnu-thread-multi-64int > (with 41 registered patches, see perl -V for more detail) I think this started showing up for me for perl 5.20. Let me go checkout linux-next and see if that fixes anything or not... thanks, greg k-h

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How to safely access inode/dentry obtained from struct page *?
by Joshi Sept. 4, 2014

Sept. 4, 2014

I am trying to obtain file name at block layer level (above IO scheduler). At this level I receive bio structure, within which page pointers are kept. Thereby I do following to obtain the inode and dentry - struct inode *inode_ptr = page->mapping->host; if (inode_ptr != NULL) /* Access dentry i.e. i_dentry in the inode */ This works usually. But problem is, inode and dentry may get released from inode and dentry cache at any time. While accessing inode/dentry I need to ensure that till the time I am accessing'em these structure remain valid in memory. Is it possible to ensure that? Which structures/locks I need to check for the purpose. Appreciate any help. Thanks! -- Joshi

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Resources to teach from C to Kernel Development?
by Ed Holmes Sept. 2, 2014

Sept. 2, 2014

Can you recommend me any books or online resources to teach a C programmer Kernel development? I can program in C but I don't really know where to go from there. I've tried the Eucalyptus challenge but it just suggests things to try. No actual tutorial.

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Test Hardware
by nick Aug. 31, 2014

Aug. 31, 2014

Hey Guys, I am wondering what test system(s)/hardware specs I need for testing btrfs code as I am wondering due to thinking about a future budget for it. Cheers Nick

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kbuild: kselftest error
by Drew Fustini Aug. 30, 2014

Aug. 30, 2014

Hi - I noticed the kselftest target in the kernel Makefile and decided to try it out of curiosity: afustini@lappy486:~/dev/linux/lappy486/git/kernels/mainline$ sudo make kselftest Has anyone run kselftest successfully? I ran into an error that I'm trying to figure out: == Testing sysctl behavior against /proc/sys/vm/swappiness == Writing test file ... ok Checking sysctl is not set to test value ... ok Writing sysctl from shell ... ok Resetting sysctl to original value ... ok Writing entire sysctl in single write ... ok Writing middle of sysctl after synchronized seek ... FAIL Writing beyond end of sysctl ... FAIL Writing sysctl with multiple long writes ... ok make[2]: *** [test_num] Error 1 ./fw_filesystem.sh: timeout works ./fw_filesystem.sh: filesystem loading works fw_filesystem: ok ./fw_userhelper.sh: timeout works ./fw_userhelper.sh: firmware interface never appeared fw_userhelper: [FAIL] make[2]: *** [fw_userhelper] Error 1 make[1]: *** [run_tests] Error 2 make: *** [kselftest] Error 2 I'm running kernel that I compiled from linus's tree 2 days ago. After encountering the error, I turned on all the testing config options I could find under the kernel hacking category. However, I encountered the same kselftest error with the newly built kernel: Linux lappy486 3.17.0-lappy486-00040-gff0c57a-dirty #5 SMP PREEMPT Thu Aug 28 05:08:04 CDT 2014 x86_64 x86_64 x86_64 GNU/Linux Log files for reference: make-kselftest-3.17.0-lappy486-00040-gff0c57a-dirty.log: https://gist.github.com/pdp7/79d511ddf30fa8d0dfee dmesg-3.17.0-lappy486-00040-gff0c57a-dirty.log: https://gist.github.com/pdp7/ea3f86dd7dc994189c14 kernel-config-3.17.0-lappy486-00040-gff0c57a-dirty.log: https://gist.github.com/pdp7/07315ac2aba2ab4c48da lsmod-3.17.0-lappy486-00040-gff0c57a-dirty.log: https://gist.github.com/pdp7/c6db7271345afc8a6868 lib-modules-3.17.0-lappy486-00040-gff0c57a-dirty.log: https://gist.github.com/pdp7/a297c5aa246cd2b1ac9f find-sys-fs-3.17.0-lappy486-00040-gff0c57a-dirty.log: https://gist.github.com/pdp7/9238072c1630e0995749 git-status-3.17.0-lappy486-00040-gff0c57a-dirty.log: https://gist.github.com/pdp7/c300ced047d1fa7fc696 git-diff-3.17.0-lappy486-00040-gff0c57a-dirty.log: https://gist.github.com/pdp7/686ab164c55a25fcb5f8 thanks, drew

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Which Networkcards support busy polling?
by Steffen Vogel Aug. 30, 2014

Aug. 30, 2014

Hi, I'm looking for network cards which support the low latency patch set from Eliezer Tamir (Intel) which has been merged in 3.11 [1]. For me it seems like that there is currently only a single NIC driver (ixgbe) which supports this feature?! I'm currently using some e1000e cards. How hard would it be to add this busy polling functionality to this driver? Or, why is there only a single card which supports it [2]? Regards, Steffen [1] https://lwn.net/Articles/551284/ [2] Not completely true, there seems to be another Mellanox card. But this one is far to expensive for me ;-)

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In arm linux how multiple interrupt irq line mapped to the processor interrupt line ?
by Debashis Bhowmick Aug. 30, 2014

Aug. 30, 2014

Hi, As we know for arm processor have only one interrupt line, so to process multiple interrupt line, need to use PIC and interrupt vector. we know during system bootup kernel does interrupt vector table setup at a specified higher address. Now My question is when any interrupt comes how processor gets updated which irq line has been interrupted, could you please explain how actually multiple irq line mapped with the processor interrupt line? Thanks, Deba

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