- kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

PROCESS PRIORITY
by Saurabh Jain April 1, 2014

April 1, 2014

I am new to Linux kernel and I have got confused . Please can anyone give answer to my questions : Q1 -> Is static priority of a thread changes or not ? If changes then how it changes ? Q2 -> What is the default value of static priority and dynamic priority for a process and thread in Linux kernel ? Q3 -> What is the initial value of static priority and dynamic priority for a newly created thread and process? Q4 -> When we talk about the priority of a process or thread (incrementing / decrementing priority , setting priority etc. ) , then which priority we are referring , is it static priority or dynamic priority ?

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Wait for an IO to complete
by Rishi Agrawal April 1, 2014

April 1, 2014

Hi All, I want to wait in my code till the IO actually goes to the disk. For example struct buffer_head *bh=sb_bread(sb, 20) strcpy(bh->b_data, "Some Data"); /* mark and sync */ mark_buffer_dirty(bh); sync_dirty_buffer(bh); The above code only adds the bh to the request queue and returns. I need something write_buffer_to_disk(bh) Which will return only if the data has been written on disk. Please help -- Regards, Rishi Agrawal

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GOSC proposal
by sampriti neog April 1, 2014

April 1, 2014

To, I would like to participate in GOOGLE SUMMER OF CODE 2014 with your prestigious organization. I want to propose an idea regarding scanned files. My idea is to make a open source software that could scan a file directly into word document.This would be highly beneficial for direct editing.we dont need extra pdf to doc converter. For, making this i propose to use c++ language and incorporate the ocr technology to read the character individually and move them into the document.I would be really grateful if your organization take interest in my idea and suggest me more regarding my idea (if any). Looking forward to receive a quick and positive response from your side. Thanking you. Yours sincerely, Sampriti Neog

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simplefs - a ridiculosly simple file system from the scratch
by Sankar P April 1, 2014

April 1, 2014

Hi, For learning purposes, I thought I would implement a filesystem from the scratch. It has reached a state where I can do a 1.0 release. The sources are at: https://github.com/psankar/simplefs The layout is simple. The first (zeroth) block is the superblock and contains information like fs magic, number of inodes, freeblock map etc. The next block is the inode store. Creation of files and directories is supported. Nested directories are supported. A file can grow up to one block only. The data blocks for a directory contain the filename and inode number of its children. For files, it will obviously contain the actual data of the file. There are three rudimentary locks to make sure the accesses are thread safe. The 1.0 version is filled with a lot of TODOs and memory leaks. Also while implementing this, I realized that it is a bad idea to maintain the superblock and the freeblock store together in a block. So I am planning to change the on-disk layout in the next version. Apart from moving the super block to minimize locks, I am planning to implement support for extents in the next version, and journalling in the next-to-next version. The next version will take some time to come, though. But if someone wants to try filesystems from the scratch, I thought it may be useful if I share the link now itself. Also, I take this moment to thank the kernelnewbies list, especially the regular people like Mulyadi Santosa, Valdis Kletnieks, Rajat Sharma, Greg Freemyer etc. Also I would like to thank Neha Naik, Manish Katiyar who helped me with some queries during this particular implementation. I saw that Manish Katiyar has also done a similar from-the-scratch implementation and it motivated me to pursue further. Any feedback on the code is welcome. Although, I want to inform that I plan to change the locking until after I decide on a good on-disk layout for the next version, which will by-design minimize the locking needs, by splitting out freestore from superblock, keep track of children inode in a better way etc. Also I have been resisting the urge to look at ext or any other filesystem's design so as to not skew my thoughts and go with a fresh state of mind and get my own design :) Thanks. -- Sankar P http://psankar.blogspot.com

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flush_dcache_page from user space.
by ratheesh kannoth April 1, 2014

April 1, 2014

I mmap'ed mmory allocated by kmalloc , to userspace. I can modify data ( in that memory region ) from kernel space or userspace and call flush_dcache_page to get it refected in both kernel and userspace. 1) if i modify a value from userspace, is there any other way to flush dcache page from userspace. What i am looking is to avoid context switch ( to get into kernel only to call flush_dcache_page ) ? Thanks, Ratheesh

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System call interception by jprobe
by edsionte April 1, 2014

April 1, 2014

Hi, guys, I am trying to use jprobe to intercept syscalls in linux kernel. Such as open(),the original flow is open()-->sys_open(), and now, open()-->check_file()-->sys_oepn() The check_file() is jprobe's entry point. If check_file() returns sucessfully, jprobe_return() will be called and sys_open() will be running, or the open() return and user gets errno in user space. And the problem is, I have no idea what jprobe should return when I want to end open() flow. Any hint will be deeply appreciated. Thanks in advance.

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echo 1 > memory.oom_control bash: echo: write error: Invalid argument
by Kevin Wilson March 31, 2014

March 31, 2014

Hello, On Fedora 20, I try the following: 1) create a cgroup called "0" /sys/fs/cgroup/memory/0 run: echo "1" > /sys/fs/cgroup/memory/0/memory.oom_control bash: echo: write error: Invalid argument Why am I having this error ? According to the documentation: http://lxr.free-electrons.com/source/Documentation/cgroups/memory.txt: You can disable the OOM-killer by writing "1" to memory.oom_control file, as:754 <http://lxr.free-electrons.com/source/Documentation/cgroups/memory.txt#L754> 755 <http://lxr.free-electrons.com/source/Documentation/cgroups/memory.txt#L755> #echo 1 > memory.oom_control756 <http://lxr.free-electrons.com/source/Documentation/cgroups/memory.txt#L756> 757 <http://lxr.free-electrons.com/source/Documentation/cgroups/memory.txt#L757> This operation is only allowed to the top cgroup of a sub-hierarchy.758 <http://lxr.free-electrons.com/source/Documentation/cgroups/memory.txt#L758> If OOM-killer is disabled, tasks under cgroup will hang/sleep759 <http://lxr.free-electrons.com/source/Documentation/cgroups/memory.txt#L759> in memory cgroup's OOM-waitqueue when they request accountable memory.760 <http://lxr.free-electrons.com/source/Documentation/cgroups/memory.txt#L760> regards, Kevin

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Checkpatch.pl and code cleanup
by Abhijeet Kasurde March 31, 2014

March 31, 2014

Hi All, Pardon me, if this question is asked previously, Recently, I came across script in Linux Kernel called 'checkpatch.pl' which is checks coding style of a patch or file. Out of curiosity, I ran script on multiple modules and saw indentation and other errors in coding style. So question is, Can I fix them or these errors in coding style are "low hanging fruits" for now ? Thanks, Abhijeet Kasurde

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Re: Checkpatch.pl and code cleanup
by harris bohr March 31, 2014

March 31, 2014

better spend time on learning the kernel internals than coding style errors. if you improve the code, fix the check patch roots around that code and send in a patch Abhijeet Kasurde <abhijeetkasurde21(a)gmail.com> wrote: >Hi All, > >Pardon me, if this question is asked previously, > >Recently, I came across script in Linux Kernel called 'checkpatch.pl' >which is checks coding style of a patch or file. > >Out of curiosity, I ran script on multiple modules and saw indentation >and other errors in coding style. So question is, Can I fix them or >these errors in coding style are "low hanging fruits" for now ? > >Thanks, >Abhijeet Kasurde > >_______________________________________________ >Kernelnewbies mailing list >Kernelnewbies(a)kernelnewbies.org >http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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Kexec failing. How to debug further?
by manty kuma March 30, 2014

March 30, 2014

Hi, I am trying to use kexec to load new kernel but unable to load. How to debug furhter? I am working on a phone with platform x86_64. I have followed the standard steps those are mentioned in kdump.txt in linux documentation but the new kernel is not booting. I donot have serial port provision. Also, i followed the same steps on my Ubuntu PC and it works there. Any idea if we need to perform extra steps for x86_64 platform or in general for mobile devices? BR, Manty

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