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

Dynamic Sysfs Attribute Files
by Matt Davis April 24, 2013

April 24, 2013

Hello, I want my kernel module to dynamically add sysfs files for its corresponding device. Without going into detail, the attribute file will be named something like: /sys/class/myclass/mydev0/fileX where 'X' is an integer ranging from 1-256. I did not see anything in the api to allow this. I suppose I could just dynamically allocate an attribute, give it the unique name by tacking on my own integer, and pass that off to device_create_file(). However, I have not seen anywhere in the codebase where another module does this; I assume it is not allowed (or there is a better solution). The other solution (instead of sysfs) would be to add an ioctl, but this means the userland application must know the specific 'file' id to query. In the sysfs version above, the userland application can just grab the directory listing of /sys/class/myclaass/mydev0/ and see how many 'file' instances exist. -Matt

3 2

access to hardware registers using KGDB on ARM
by Андрей Скворцов April 24, 2013

April 24, 2013

Hello everyone, I have arm SoC AM3517 (Cortex-A8) running linux 2.6.32. I am trying to access hardware registers using kgdb. I can connect to the board via RS232, can read variables in kernel space, control processes using breakpoints, but I can't read hardware register. For example, I am trying to read UART3 registers. Information about UART3 is saved in structure: static struct plat_serial8250_port serial_platform_data2[] = { { .mapbase = OMAP_UART3_BASE, .irq = 74, .iotype = UPIO_MEM, .regshift = 2, ... } } mapbase is a physical address. According to the Technical Reference Manual is should be 0x49020000. I checked this field using kgdb: (gdb) p/x serial_platform_data2[0].mapbase $34 = 0x49020000 This structure has the field membase. As I understand, it contains virtual address of the mapbase physical address. This field is initialized on UART init via function ioremap(). I checked this field as well: (gdb) p/x serial_platform_data2[0].membase $35 = 0xfb020000 Now I am trying to read register MCR_REG, that has offset 0x10 from the base address. (gdb) x serial_platform_data2[0].membase+0x10 0xfb020010: Cannot access memory at address 0xfb020010 (gdb) x serial_platform_data2[0].mapbase+0x10 0x49020010: Cannot access memory at address 0x49020010 As I understand, the membase address should work. Right? Why has access failed? Is it kgdb limitation? -- Best regards, Andrey Skvortsov

1 0

[HELP] cpuidle in SYSFS: /sys/devices/system/cpu/cpu0/cpuidle/state0/desc
by Ren Zhen April 24, 2013

April 24, 2013

Hi all: In /Documentation/cpuidle/sysfs.txt, It says: "desc : Small description about the idle state(string)". when I read desc: ------------------------------------------------------------------------ mysystem:/sys/devices/system/cpu/cpu0/cpuidle/state0/# cat desc CPUIDLE CORE POLL IDLE ------------------------------------------------------------------------ Here is my question:What the meaning of ‘CPUIDLE CORE POLL IDLE'? Any help will be appreciated! -- Sincerely, Ren Zhen

1 0

Fwd: Building kernel modules with debuginfo and printing line numbers in kernel oops message / coredump
by Sankar P April 24, 2013

April 24, 2013

On Mon, Apr 22, 2013 at 6:00 AM, arshad hussain <arshad.super(a)gmail.com> wrote: > > > > On Mon, Apr 22, 2013 at 5:58 AM, arshad hussain <arshad.super(a)gmail.com> > wrote: >> >> >> >> >> On Fri, Apr 19, 2013 at 11:55 PM, Sankar P <sankar.curiosity(a)gmail.com> >> wrote: >>> >>> 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 >>> >>> _______________________________________________ >>> Kernelnewbies mailing list >>> Kernelnewbies(a)kernelnewbies.org >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> >> >> "myfunctionname +0x2507 +5679" >> >> It's not hex gibberish. What it saying is that, at the time of crash the >> EIP was pointing >> withing function "myfunctionname" and offset 0x2507 bytes. Use objdump >> binary to >> more detail of your simple.ko >> Thanks. But is there not a way to get the line numbers and filenames printed automatically instead of the memory addresses ? For example, in gdb, in userspace, if there is a crash, we can get the line numbers printed when there is a crash. Can the kernel crash/oops handler similarly not print the filenames and linenumbers automatically ? Is there a configuration or hack for getting it that way ? -- Sankar P http://psankar.blogspot.com -- Sankar P http://psankar.blogspot.com

2 1

Re: [rrd-users] Can small writes generate a lot of faults?
by Daniel Hilst Selli April 23, 2013

April 23, 2013

Em 20/04/2013 09:09, Tobi Oetiker escreveu: > hi daniel > > On 19.04.2013, at 16:42, Daniel Hilst Selli <danielhilst(a)gmail.com> wrote: > >> AFAIK, major page faults are generated when data that is not yet present >> on RAM is loaded from disk, but in this case data is being write do >> disk, I can't >> see how writes can generate faults, but still, it seems that is >> happening, ... !? >> > rrdtool changes just few bytes in the rrf file with each update > > the OS though can only write a complete block of data to disk. > > so when you write a byte to a file, the OS has to first fetch the block, modify the byte and write the block back > > that is why rrdtool benefits greatly from more RAM as it can hold mor blocks in RAM and does not have to read them first. > > cheers tobi > Thanks Tobi, I had no idea about this read/update/write process, Now I know how to improve the performance of my collectd+rrdtool stuff, Cheers

1 0

Can small writes generate a lot of faults?
by Daniel Hilst Selli April 23, 2013

April 23, 2013

My case is this, I'm using collectd [1] with rrdtool [2] to monitor some server. a) When I enable rrdtool plugin I can grab collectd process as top page fault process on top command. PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ nFLT COMMAND 20128 root 18 0 4105m 35m 17m S 7.9 0.3 0:09.62 22k /opt/collectd/sbin/collectd b) Disabling rrdtool plugin dramastically decrease the number of page faults of collectd. c) I know that rrdtool plugin is known to generate a lot of small writes, as stated in [3]. Also I know the parameters to improving collectd's cache usage to save I/O, but this is not the question here.. AFAIK, major page faults are generated when data that is not yet present on RAM is loaded from disk, but in this case data is being write do disk, I can't see how writes can generate faults, but still, it seems that is happening, ... !? Is that possible? Cheers, [1] http://www.collectd.org [2] http://oss.oetiker.ch/rrdtool/ [3] https://collectd.org/wiki/index.php/Inside_the_RRDtool_plugin

4 4

Writing device drivers in Linux: A brief tutorial
by Zack April 23, 2013

April 23, 2013

I thought this might be useful: http://www.freesoftwaremagazine.com/articles/drivers_linux -- Zachary

4 3

Invitation to connect on LinkedIn
by Vivek P. April 23, 2013

April 23, 2013

LinkedIn ------------ Vivek P. requested to add you as a connection on LinkedIn: ------------------------------------------ Deepak, I'd like to add you to my professional network on LinkedIn. - Vivek Accept invitation from Vivek P. http://www.linkedin.com/e/8z2206-hfuyp8yy-a/L90NvsYL3GREvJdnM0f-HnfkWNbSD_6… View profile of Vivek P. http://www.linkedin.com/e/8z2206-hfuyp8yy-a/rso/86727318/UjWT/name/49489491… ------------------------------------------ You are receiving Invitation emails. This email was intended for Deepak Shah. Learn why this is included: http://www.linkedin.com/e/8z2206-hfuyp8yy-a/plh/http%3A%2F%2Fhelp%2Elinkedi… (c) 2012, LinkedIn Corporation. 2029 Stierlin Ct, Mountain View, CA 94043, USA.

2 1

what will kernel_execve() does..?
by sandeep kumar April 23, 2013

April 23, 2013

Hi All I m having a doubt about.. what kernel_execve() does...? As per the comment it should make the kernel thread a user space process. I am doing a kernel bringup. while launching the init process, i was struck in this function... kernel_execve() in arch./arm/kernel/sys_arm.c I am feeling i was struck in some kind of infinite loop here..and program control is not reaching till user space init process's main function. *Can someone tell me, is there any condition that i am missing here, failing which the kernel will struck in infinite loop and doesnt switch to user space?* -- With regards, Sandeep Kumar Anantapalli,

1 0

[HELP] Document: /sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size
by Ren Zhen April 23, 2013

April 23, 2013

Hi everybody, For /sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size, I execute the cmd '#cat coherency_line_size',then it return '64'. My OS is Ubuntu 12.04, CPU is intel core i3. Here is my problem, what is coherency_line_size ? what is its usage? Any help will be appreciated! Sincerely, Ren Zhen

2 1