April 2013 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

I2C: kernel & userspace drivers : using i2c-stub
by Sagar Padhye April 23, 2013

April 23, 2013

Hi, [USING : Ubuntu 12.04 LTS] I am trying to learn I2C subsystem. I havent found much of well documented things that can help a newbie on google. I just chose to read the linux kernel documentation txts. I read the way kernel can interact with i2c through both SMBus calls & raw file op calls (ioctl, read, write). It looks good till that point. The doc also tells about i2c stub. which can be used as follows: 1. load the i2c module 2. use i2cset (from the i2c-tools project) to pre-load some data 3. load the target chip driver module 4. observe its behavior in the kernel log I was able to achieve just the 1st step here. I loaded the module successfully. $ sudo modprobe i2c-stub chip_addr=0x023 I got following Kern msg $dmesg ... [658.071706] i2c-stub: Virtual chip at 0x23 So I believe that step 1 is clear. in second step I have no idea how to provide needed inputs to command -> Usage : i2cset [-f] [-y] [-m mask] I2CBUS CHIP-ADDRESS DATA-ADDRESS [VALUE] [MODE] I tried to give I2CBUS = 0, Chip addr = 0x23 & data addr=0 but it gives error Error : Could not open file '/dev/i2c-0' or '/dev/i2c/0' : No such file or directory There is no file at all created in /dev corrosponding to this device. Any idea how to use i2c properly? Is this an ubuntu only problem? Can anybody provide a good tutorial like thing to learn about i2c kernel & userspace driver programming? -- Thanks and Regards, Sagar

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Fwd: [RFC]CPU in SYSFS: what information should be written to /sys/devices/system/cpu/probe to add cpu In X86?
by Ren Zhen April 22, 2013

April 22, 2013

Hi, everybody: What information should be written to /sys/devices/system/cpu/probe to add a cpu In X86? And, what information should be written to /sys/devices/system/cpu/release to remove a cpu In X86? I have read the /Documentation/ABI/testing/sysfs-devices-system-cpu. It says that probe:writes to this file will dynamically add a CPU to the system. Information written to the file to add CPU's is architeture specific. release: writes to this file will dynamically remove a CPU to the system. Information written to the file to remove CPU's is architeture specific. I just want to know what information should be written to those file. Any help will be appreciated! -- Sincerely, Ren Zhen

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Alternative for API system() in multi-threaded app
by Praveen kumar April 22, 2013

April 22, 2013

I was trying to replace system() API in my multi-threaded app as it is suggested not to any calls in multi-threaded app which uses fork()..... When I was going through the man pages of fork()..in the Notes section I found * "Since version 2.3.3, rather than invoking the kernel's fork() system call, the glibc fork() wrapper that is provided as part of the NPTL threading implemenâ* * tation invokes clone(2) with flags that provide the same effect as the traditional system call. The glibc wrapper invokes any fork handlers that have been* * established using pthread_atfork(3)."* Is this mean, I still can use fork() or any other API which uses fork() for its implementation and make sure my app is thread safe or free from dead locks???? Thanks, Praveen R

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Something about Redhat
by Robert Clove April 21, 2013

April 21, 2013

Hi, I want to learn so i found somethings to ask here...... I had an red hat machine i forgot the password so i change it to single user and break the password . NOW, I want to know how to 1)Switch it back to multi user mode? 2)how to know which service are running and how to stop services 3)how to get the machine to receive the dynamic ip i mean how to make dhcp enable. 4)how to make multiple users work at the same time. Thanks

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process context value
by Shraddha Kamat April 21, 2013

April 21, 2013

I was reading about PowerPC-64 address translation and stumbled upon a term 'process context value' - googled but could not find much details about this - please help. regards, Shraddha

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Building kernel modules with debuginfo and printing line numbers in kernel oops message / coredump
by Sankar P April 21, 2013

April 21, 2013

Hi, I have written a kernel module which I build using: Makefile (edited a bit) ========== obj-m := simple.o simple-objs := s.o make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules ======= Everything builds fine. But my kernel module caused an oops and the message was something like: myfunctionname +0x2507 +5679 or some hexadecimal gibberish. I know that I can use some external tool to find out what these addresses mean. But, is there a way I can get the kernel oops message to print these information along with line number ? Is there a way to build the kernel module with debug symbols ? In user space, I usually do "-g" or "-ggdb" and it will give me line numbers and filenames neatly while dumping stacktrace. Is there a similar facility available for out of tree kernel modules too ? Even if I give : $ CFLAGS="-ggdb" make The output file size (.ko) is not changed. Can someone help me with building kernel modules with debug info and get the filename and line numbers printed in the oops messages / coredump ? Thanks. -- Sankar P http://psankar.blogspot.com

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YAFFS2 not part of Linux Kernel
by Pietro Paolini April 20, 2013

April 20, 2013

Hello all, reading docs and browsing internet I read that YAFFS2 is not merged in the Linux Kernel and that we should add it as a patch, the date is not write on that documents and I just tried to search YAFFS2 on the latest linux kernel source without relevant results. Then after a look on the www.yaffs.net I discovered a tutorial for merge it and I am sure, yes is not in the kernel tree. On the website they said is under the GPL license and I don't understand, why is not merged in the Linux Kernel directly ? It's just a curiosity, thanks in advance. Pietro.

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Check live Virtual Address to Physical Address mappings
by Shraddha Kamat April 19, 2013

April 19, 2013

I want to see live Virtual Addr. to Physical Addr. mappings for a process. is it possible to see such mappings ( for e.g. under /proc etc ..). Regards, Shraddha

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Why the niceness is not always taken into account ?
by Alexandre Laurent April 19, 2013

April 19, 2013

Hello, I have some questions about nice and programs scheduling. My machines have an 8 cores CPU. I am using an CPU intensive test, using OpenMP and running on the 8 cores for the experiments. When I am running my test it is taking around 12s. If I am starting at the same time two instances of this test it takes 24s which is totally fine and expected. I wanted to prioritize one instance of the test with nice. To do this, I am applying a niceness of -20 to privileged one, and setting a niceness of 20 to "slow down" the second one. This is usually working well. The privileged one with run around 12s (so, at full speed) and the other one 24s (-> paused for 12s and running the 12 last seconds at full speed). My problem is that in some cases it is not working at all. It works fine if I am running both programs in the same instance of the terminal, or from a script (so, same instance of interpreter). But this is not working if I am running the instances in separate SSH session. When I say it is not working, both instances will take 24s to run and the CPU usage is just shared between the tasks. More precisely : I am running the same test, but connecting twice on the remote machine (one connection by test instance). I am using exactly the same commands than during the others experiments. But, by using two SSH instances, the niceness will not be taken into account. The CPU will be shared equally between both instances even if htop is showing a niceness of 19 / -20 for the low priority program and the privileged program respectively. (For information, if I am running my program throught SSH using a script, and even by running the commands directly throught the SSH terminal it will work as expected. So, the cause is not on SSH.) Can you explain me, why in such case, the niceness is not taken into account ? Can you tell me how I can workaround this problem to effectively set niceness and get it respected by the system ? Best regards,

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help needed to do mmap
by er krishna April 19, 2013

April 19, 2013

Hi All, I am trying to do mmap from user space program to fetch physical memory base address B202E7000 and size F0. But I am getting operation not permitted error. Any suggestion by which I can increase the privilage by sysctl to acess this reason ? Krishna

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