April 2015 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Question about DC-DC frequency handling
by Stefan Wahren April 26, 2015

April 26, 2015

Hi, i'm current working on a regulator driver which should be able to change DC-DC clock frequency. Now here is my question. What is the prefered way to implement the clock handling? Option A): The regulator driver handles all internally (select clock source, set frequency). Option B): The DC-DC clock domain is implemented in the clock driver and the regulator driver uses the clock framework. Best regards Stefan

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task dequeue
by Mustafa Hussain April 24, 2015

April 24, 2015

When the task should be dequeued in CFS?

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perf tool
by Abhishek Bist April 24, 2015

April 24, 2015

Hi, I am looking for a best tutorials or links to learn and exploit the features of a perf tool. I already googled it and try to use it at minimal level.But looking for a link so that i could use it as a benchmark for some testing on kernel level espicially on process management section.

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How can I fetch the files likely directory /usr/src/kernels/<kernel version> from kernel source tree?
by tianlilai April 24, 2015

April 24, 2015

Hi,I have built the kernel source tree and running in PC mechine.Now I want to fetch the files likely directory /usr/src/kernels/<kernel version> from this kernel source tree.How can I do? Thanks very much!

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about memory zone usage
by yoma sophian April 24, 2015

April 24, 2015

hi all: in buddy allocator heart function, __alloc_pages_nodemask, I found we use zonelist-> _zonerefs to iterate all the zone in NUMA or UMA. My questions are: 1. the advantage of travelling zonelist-> _zonerefs instead of iterating zones on each node is because it is faster, right? 2. zonelist-> _zonerefs has recorded information of each zone, under what circumstances we will iterated zone of node to get zone's data instead of zonelist-> _zonerefs appreciate your help in advance,

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Links to understand File System
by sahil aggarwal April 24, 2015

April 24, 2015

Hi all, I am reading Understanding the linux kernel CH15(ext2 and ext3 file systems) and have even started implementation of File system from scratch for learning purpose by following this : https://github.com/psankar/simplefs Any leads on other links/papers to understand VFS->FS->disk flow better.? Thank you Sahil

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How to read write PCI BAR memory address
by Anil Joshi April 24, 2015

April 24, 2015

My PCI device information is as follows: Print Begin Configuration space... BAR 0 start address: f6000000 BAR 0 end address: f6ffffff BAR 0 flags: 140204 BAR 0 IO / MEM: MEM BAR 0 PREFETCH NON PREFETCH: NON-PREFETCH BAR 1 start address: 0 BAR 1 end address: 0 BAR 1 flags: 0 BAR 1 IO / MEM: MEM BAR 1 PREFETCH NON PREFETCH: NON-PREFETCH BAR 2 start address: f0000000 BAR 2 end address: f3ffffff BAR 2 flags: 14220c BAR 2 IO / MEM: MEM BAR 2 PREFETCH NON PREFETCH: PREFETCH I want to write a byte and read it back to BAR2 for a test simple . Is it possible to write a byte to BAR2 start address Sample code is welcomed. Regards

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Re: How can I fetch the files likely directory
by Avinash Sridharan April 23, 2015

April 23, 2015

Pull a git repository from git:// git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git and create branch for the specific version of kernel that you are interested in. The http://kernelnewbies.org/KernelBuild gives all the instructions under the "Which kernel to build?" section. On Thu, Apr 23, 2015 at 9:00 AM <kernelnewbies-request(a)kernelnewbies.org> wrote: > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. How can I fetch the files likely directory > /usr/src/kernels/<kernel version> from kernel source tree? > (tianlilai) > 2. execve error (Rohith) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 23 Apr 2015 17:59:56 +0800 > From: tianlilai <laitianli2015(a)outlook.com> > Subject: How can I fetch the files likely directory > /usr/src/kernels/<kernel version> from kernel source tree? > To: kernelnewbies(a)kernelnewbies.org > Message-ID: <BLU436-SMTP88F0913B3897AE70E7C950A9ED0(a)phx.gbl> > Content-Type: text/plain; charset="utf-8"; format=flowed > > > Hi,I have built the kernel source tree and running in PC mechine.Now I > want to fetch the files likely directory /usr/src/kernels/<kernel > version> from this kernel source tree.How can I do? Thanks very much! > > > > > ------------------------------ > > Message: 2 > Date: Thu, 23 Apr 2015 17:55:22 +0530 > From: Rohith <itsnotrohit(a)gmail.com> > Subject: execve error > To: kernelnewbies(a)kernelnewbies.org > Message-ID: > < > CABsTBT6S0vRNFo0bxxBcWDx3k8JMpzbYyKbbUB8oxT-W%2B8Tr-A(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Hi all, > > I'm facing a strange issue with execve. It fails with -EFAULT > intermittently. I found that whenever it failed the stack allocated to the > process is in the last page of the CONFIG_TASK_SIZE. > > For example, if CONFIG_TASK_SIZE is set to 0x4000_0000, the process would > fail in execve if the stack happens to be in the page: > > 3ffdf000-40000000 rw-p 00000000 00:00 0 [stack] > > I tried changing CONFIG_TASK_SIZE=0x30000000 and the process this time > fails at the end 0x30000000 address. > > I also found that the execve seem to use the largest stack address > (STACK_TOP_MAX, function __bprm_mm_init(), fs/exec.c) while copying > argv/envp to the new process space. > > I don't know how to debug further. I feel that the user process stack > should never be allocated at the CONFIG_TASK_SIZE? Any idea or suggestion > on how to debug further, please tell me. > > thanks, > rohit >

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execve error
by Rohith April 23, 2015

April 23, 2015

Hi all, I'm facing a strange issue with execve. It fails with -EFAULT intermittently. I found that whenever it failed the stack allocated to the process is in the last page of the CONFIG_TASK_SIZE. For example, if CONFIG_TASK_SIZE is set to 0x4000_0000, the process would fail in execve if the stack happens to be in the page: 3ffdf000-40000000 rw-p 00000000 00:00 0 [stack] I tried changing CONFIG_TASK_SIZE=0x30000000 and the process this time fails at the end 0x30000000 address. I also found that the execve seem to use the largest stack address (STACK_TOP_MAX, function __bprm_mm_init(), fs/exec.c) while copying argv/envp to the new process space. I don't know how to debug further. I feel that the user process stack should never be allocated at the CONFIG_TASK_SIZE? Any idea or suggestion on how to debug further, please tell me. thanks, rohit

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Basic question about malloc
by Abhishek Bist April 23, 2015

April 23, 2015

On Thu, 23 Apr 2015 09:52:56 +0800, æ…•å†¬äº® said : I'm looking for that whether the object allocated by malloc is the multiple of certain bytes! Or how does the malloc allocate dynamic memory ?? I does an experiment in my computer! #include<stdio.h> #include<stdlib.h> #define NUM 33 int main(int argc,const char *argv[]) { char *a, *b, *c; a = malloc(NUM); b = malloc(NUM); c = malloc(NUM); printf("a = %x\n",a); printf("b = %x\n",b); printf("c = %x\n",c); free(a); free(b); free(c); return 0; } But the result has no feature about a ,b ,c! Can someone tell me what's wrong with me? My GCC version is gcc (Debian 4.9.2-10) 4.9.2 mudongliang Hey, ASFAIK you are looking for the number of bytes allocated to you after calling malloc.First of all malloc is not a function of a kernel space. The dynamic memory allocation of a memory are generally done by brk(),sbrk(),mmap() etc .And you could easily check these using a strace tools.[ strace ./a.out ].And in general the number fo bytes allocated to you from a pool is mentioned just 8 bytes behind (in case of character) the starting address allocated to you and you could check it by just derefrencing it.It is a location which is generally fetched by the free call while freeing a memory from a pool.But there are a memory leakages in case of dynamic memory allocation in C. Please, correct me if I am wrong. And i am bit uncertain about the so called " featuring of a, b and c"

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