August 2012 - 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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Finding the interrupt vector of a given IRQ
by Mark Farnell Oct. 20, 2012

Oct. 20, 2012

In the kernel, how can I find out the interrupt vector number of a given IRQ (for example, IRQ7)? Within the kernel module, I would like to manually set the IRQ using the assembly code: asm("int $<irq vector>"); and let the IRQ handler installed by a different module catch that interrupt. Is this possible? Thanks! Mark

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compile kernel 3.0.34 errors
by wenrongbupt Sept. 14, 2012

Sept. 14, 2012

Hi guys, I am using Fedora 13(kernel version is 2.6.33.3-85.fc13.i686.PAE) and try to build kernel 3.0.34. I am follow these steps: make mrproper make bzImage make modules make modules_install make install Every step is succeed except make install It has following errors: ERROR: modinfo: could not find module twofish ERROR: modinfo: could not find module i2c I don't know how to solve this problem.Please help me!Thank you very much. Regards Vincent

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Writing I2C chip driver in combination with other structure
by aurum spark Sept. 4, 2012

Sept. 4, 2012

Hi All, I have written and seen lot of code of i2c drivers for input subsystem devices and much familiar with that. Now I have started writing driver for one chip that is not exactly type of input device. So, little bit confused about how should be the driver architecture so that it will be a clean code yet simple. Following text and diagram explains short functional description of chip. Chip Interface :- ========== ====== ======= | | | I2C | | | ----- I2C --- | Device | | ARM | ----- Bus -- | With rw | ------------ Input Connect | | | regs | | | ---------------| | ====== INTR ======= So above picture depicts how chip is interfaced to ARM CPU. This chip has some registers which are rw and can be used to read certain information from chip or to program it. This chip is capable of giving intterupt to CPU. This chip has one input which it like some cable connection. It detects when this cable is connected and raises the interrupt. Functionality Expected in Driver:- =================== 1. Driver should communicate with chip over I2C. 2. Driver should report event to user space upon receiving interrupt from I2C device. 3. Driver should be capable of programming I2C chip @ the time of initialization as well should be capable of changing registers as and when Linux User Space application wants to. What I have thought of:- ============== #1 definitely makes this as i2c client driver(chip driver) #2 Here I have few options a) Shall I use input subsystem mechanism to report interrupt as an event to user space ? In this case it's combination of I2C + input subsystem. Then application can read something over i2c and decide next flow, OR b) Shall I use some sysfs based interface on which application can do select sys call and can receive event ? for this nothing extra required. #3 Since approach in #2 is not fixed here also there are multiple options a) This can be written as I2C client + char driver so that it can have ioctls to send commands to i2c chip based on applications demand. b) We can provide sysfs interface to user space to send commands to i2c device as and when required at runtime. As per my thoughts I am not sure shall I make this as input device just to report one event upon getting interrupt from device. Also will it be ok to have this as char driver in combination with i2c chip driver ? Please guide me and take me to correct source or documentation or to source code of some driver for this kind of device. Does i2c support ops like fbops ? Regards, ~/Aurum

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Difference between kernel 3.0.15 and kernel 3.4
by Ritesh Harjani Sept. 3, 2012

Sept. 3, 2012

Where i can find all the differences between the kernel version 3.0.15 and 3.4. Ritesh

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How to understand the macro __init?
by 王哲 Sept. 3, 2012

Sept. 3, 2012

hi all in the kernel modules,we often use the macro __init. if we only discuss the __init for functions.__init tells the compiler to put the function in a special section.and the function are used once.So the code of this function should be freed from the memory after the first call. so i write a sample module: #include <linux/module.h> #include <linux/init.h> void __init print_k(void) { int k = 9; printk("<0>k = %d\n",k); } static int __init hello_init(void) { printk("<0>hello kernel!\n"); print_k(); print_k(); return 0; } static void __exit hello_exit(void) { printk("<0>bye kernel!\n"); } module_init(hello_init); module_exit(hello_exit); MODULE_LICENSE("GPL"); i use the __init for function print_k. in my opinion after the fisrt invoking the print_k in the hello_init. the memory of print_k will be freed,and the second invoking will not be executed.but the result of second invoking is executing . why? Thanks in advance! wanny

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Kernel booting problem.
by Sri Ram Vemulpali Sept. 2, 2012

Sept. 2, 2012

Hi All, I compiled my own kernel image with uclibc cross tool chain for x86 i686 arch. I am using grub as boot loader. these are the following parameters I am giving. kernel /bzImage ro root=/dev/VolGroup00/LogVol00 rhgb quiet init=/sbin/init initrd /initrd.img -----> this is cpio image of filesystem structure with needed modules and lib When I select at grub options to boot the kernel after reading bzImage grub proceeds to initrd and stuck at initrd. There is no output. I searched online and I found other kind of problems. But this is something different. Can anyone give some suggestions. Thanks in advance. -- Regards, Sri.

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map bss to addr zero
by Srinivas Ramanan Sept. 2, 2012

Sept. 2, 2012

Hi all, This is an interview question. "What is the implication of mapping BSS to the Virtual Memory Segment 0?" I was not able to find the answer from web. So posting here. thanks, srinivas

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Is my rootfs correctly mounted?
by stl Aug. 31, 2012

Aug. 31, 2012

Hello all, if I try to boot Linux 2.6.37 by supplying a configuration file to the kernel to create initramfs_data.cpio, (without any compression), is it normal that the kernel doesn't print the well known message: VFS: Mounted root (<type> filesystem) even if the boot reaches the point where it tries to run init executable? Does it mean that my rootfs is not correctly mounted? Here is the kernel output printed during the boot: <5>[ 0.000000] Linux version 2.6.37+ (gcc version 4.6.3 20120816 (GCC) ) #57 Thu Aug 30 12:00:00 CEST 2012 [ 0.000000] Built 1 zonelists in Zone order, mobility grouping off. Total pages: 2032 [ 0.000000] Kernel command line: [ 0.000000] PID hash table entries: 32 (order: -5, 128 bytes) [ 0.000000] Dentry cache hash table entries: 1024 (order: 0, 4096 bytes) [ 0.000000] Inode-cache hash table entries: 1024 (order: 0, 4096 bytes) [ 0.000000] Memory: 7656k/8196k available (1098k kernel code, 536k reserved, 2096117k data, 12k init) [ 0.000000] SLUB: Genslabs=15, HWalign=16, Order=0-3, MinObjects=0, CPUs=1, Nodes=1 [ 0.000000] NR_IRQS:64 [ 0.000000] Timer start: timer interrupt every 10 ms [ 0.000000] console [ttyS0] enabled [42949372.980000] Calibrating delay loop... 0.00 BogoMIPS (lpj=0) [42949373.180000] pid_max: default: 32768 minimum: 301 [42949373.200000] Security Framework initialized [42949373.210000] Mount-cache hash table entries: 512 [42949373.260000] khelper used greatest stack depth: 7548 bytes left [42949373.340000] kworker/u:0 used greatest stack depth: 7324 bytes left [42949373.500000] bio: create slab <bio-0> at 0 [42949373.630000] kworker/u:0 used greatest stack depth: 7260 bytes left [42949374.630000] kworker/u:0 used greatest stack depth: 7180 bytes left [42949375.250000] VFS: Disk quotas dquot_6.5.2 [42949375.270000] Dquot-cache hash table entries: 1024 (order 0, 4096 bytes) [42949375.390000] msgmni has been set to 16 [42949375.420000] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 253) [42949375.430000] io scheduler noop registered [42949375.440000] io scheduler deadline registered [42949375.460000] io scheduler cfq registered (default) [42949375.490000] Architecture Specific Serial Driver [42949375.500000] ttyS0 at MMIO 0x40001000 (irq = 5) is a arch_uart [42949375.700000] loop: module loaded [42949375.720000] mice: PS/2 mouse device common for all mice [42949375.780000] ------------[ cut here ]------------ [42949375.800000] WARNING: at fs/proc/generic.c:589 .LBE364+0x0/0x2() [42949375.810000] proc_dir_entry '/proc/schedstat' already registered [42949375.820000] Modules linked in: [42949375.830000] ---[ end trace 31baa4bbf69a8bbc ]--- [42949375.850000] Failed to execute /init [42949375.870000] Kernel panic - not syncing: No init found. Try passing init= option to kernel. See Linux Documentation/init.txt for guidance. In my opinion, it seems to be correct because the following message doesn't appear: Warning: unable to open an initial console This means that the file /dev/console has been found, so that the rootfs has been correctly mounted, isn't it? Thanks in advance for your help!

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Re: Issue with ps -l command "Unknown HZ value! (744514) Assume 100."
by Mulyadi Santosa Aug. 30, 2012

Aug. 30, 2012

Hi... please, don't top post... On Thu, Aug 30, 2012 at 6:51 PM, KARTHIK SEKURU <karthik.sekuru(a)gmail.com> wrote: > > If yes,then would replacing the linux-3.4.tar.bz2 with the one > modified(having CONFIG_HZ as 25) by me would make the userspace take 25HZ as > default.Am i correct? can't guarantee that, but I think it's worth to try.... -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com

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