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/proc help
by Surenkumar Nihalani Feb. 9, 2012

Feb. 9, 2012

Hi guys, I want to find the number of threads owned by the caller process who tried to read from my proc file, how do I find the stuct responsible for it? Also, I want to know the thread id of my caller. I am writing a kernel module. Please help. Thanks, Suren.

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Re: Google Summer of Code 2012
by Peter Senna Tschudin Feb. 8, 2012

Feb. 8, 2012

Hi Greg, :-) > kernelnewbies has not been involved in GSoC before, there are different > groups handling kernel related projects with GSoC. PSU and the Linux > Foundation are two of them. I asked here due: http://www.linuxfoundation.org/collaborate/workgroups/gsoc/2011-gsoc-kernel… Any idea about how to get involved in Linux Foundation Google Summer of code? Thank you! -- Peter Senna Tschudin peter.senna(a)gmail.com gpg id: 48274C36

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page replacement policy in the latest Linux kernel
by Zheng Da Feb. 8, 2012

Feb. 8, 2012

Hello, I'm trying to understand the page replacement policy in the latest Linux kernel and reimplement a similar one in the user space. As far as I can understand from ULK and the code, there are two lists: active list and inactive list. Here I only consider the case of the *page cache*: When a page is added to the page cache (by add_to_page_cache_lru), it is also added to the inactive list and its reference bit is set (by mark_page_accessed). When a page is accessed again, it is added to the active list and the reference bit is cleared (by mark_page_accessed). When a page is accessed and it's in the active list, the reference bit is set if it's not set (by mark_page_accessed). When the system is out of free pages, it starts to shrink the cache. When a page is in the active list, if the page hasn't been referenced for a period of time (page_referenced() returns 0, and for the pages in the page cache, it's always 0), it will be moved to the inactive list (in shrink_active_list); When a page is in the inactive list, if the page hasn't been referenced (it's always true for pages in the page cache), reclaim the page (in shrink_inactive_list); When the system is out of free pages, it always starts to reclaim pages in the inactive list first, unless the number of pages in the active list is larger than that in the inactive list. Please correct me if any part is wrong for the page cache. Thanks, Da

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blktrace vs ftrace
by Matthias Brugger Feb. 8, 2012

Feb. 8, 2012

Hi all, I'm trying to analize I/O behavior of Qemu on the host. I used blktrace and the blk tracer for ftrace but I see different I/O behavior. I use 4 threads in the VM each reading sequentially a file. Readahead is turned off. With blktrace reads are transmitted in a sequential way, which means the next read will be executed when the first one has completed. In comparison with ftrace, up to 4 reads are issued to the disk in parallel. I suppose the different behaviors are due to the overhead introduced by the tracers. My doubt is, which tracer has less influence on the I/O behaviour and therefore reflects the system behaviour without tracing. Thanks a lot, Matthias --- http://motzblog.wordpress.com/

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Contribute to linux kernel
by Mayank Agarwal Feb. 8, 2012

Feb. 8, 2012

Dear Experts, I want to contribute to linux kernel in camera drivers or in any of the multimedia related driver development linux kernel job. Please send me the details how can i start doing this. Thanks and Regards, Mayank

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Google Summer of Code 2012
by Peter Senna Tschudin Feb. 8, 2012

Feb. 8, 2012

Hello, Are there plans for 2012 GSoC Kernel works? Is this the right place for asking? Regards, Peter -- Peter Senna Tschudin peter.senna(a)gmail.com gpg id: 48274C36

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Re: 答复: parent inode from the current struct inode
by Jack David Feb. 8, 2012

Feb. 8, 2012

2012/2/8 Tom Lai(IT) <tomlai(a)utstar.com>: > Hi Philipp, > > I checked 2.6.32 that dentry struct contained parent dentry struct. > > > Hi Jack, > > On Wed, Feb 8, 2012 at 8:48 AM, Jack David <jd6589(a)gmail.com> wrote: >> Hi All, >> >> Is possible to get parent directory's inode structure from the current >> inode? If so, how can I do that? > > It should be possible to use the container_of macro to get the parent > dentry struct. Then, you can get the parent dentry d_parent and access > its inode. (Please correct me, if I'm wrong. I didn't test it). > Okay, I tried container_of, but it did not work. So I tried d_obtain_alias() which worked. But I am not sure if I have to make a call to dput() as well in order to free the dentry obtained. Anyone can confirm this? J > > > Philipp > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies -- J

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fork() and exec()
by Vijay Chauhan Feb. 8, 2012

Feb. 8, 2012

Hi List, I am learning Linux and trying to understand exec and fork function. execl says that it overlays the running address space. What does it mean? I created the following program and used top command with intentionally wrong arguments: #include<stdio.h> #include<unistd.h> #include<sys/types.h> #include<stdlib.h> int main(){ int a = -1; if(fork()==0){ printf("Inside child\n"); printf("child pid=%d, parentid=%d\n", getpid(), getppid()); execl("/usr/bin/top", "/usr/bin/top", ">/dev/null" ,(char*)0 ); scanf("inside child provide a %d", &a); printf("Inside child a=%d\n", a); exit(1); } else { printf("Inside parent, going to wait\n"); printf("my pid=%d, parentid=%d\n", getpid(), getppid()); scanf("input parent %d\n", &a); wait(NULL); printf("Wait over\n"); printf("Inside parent a=%d\n", a); } return 0; } When i run this program, it gives following output: [vijay@localhost]$ ./a.out Inside parent, going to wait Inside child child pid=2775, parentid=2774 my pid=2774, parentid=2681 top: unknown argument '>' usage: top -hv | -bcisSHM -d delay -n iterations [-u user | -U user] -p pid [,pid ...] 10 Wait over Inside parent a=-1 [vijay@localhost]$ Why the child scanf and printf not executed? In the parent program, i expected input parent should be printed. But it doesnt and just wait for some input. When i entered 10 it resumes but printing -1 as a value. Could anyone please help me to understand this behavior? or any good tutorial or book Thanks. Vijay

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Re: Kernelnewbies Digest, Vol 15, Issue 12
by Mayank Agarwal Feb. 8, 2012

Feb. 8, 2012

Hi all, I want to contribute to camera dri*vers in linux kernel*.Please guide me the procedure of doing that. Regards, Mayank On Tue, Feb 7, 2012 at 10:30 PM, <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. Re: "Trying to free already-free IRQ 9", but it wasn't freed > by me (mayur nande) > 2. Re: request_firmware question (Greg KH) > 3. Re: fork() and exec() (Bernd Petrovitsch) > 4. Re: make config errors while building kernel on Fedora 16 > (Kartik Singhal) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 7 Feb 2012 20:33:31 +0530 > From: mayur nande <mayur.nan(a)gmail.com> > Subject: Re: "Trying to free already-free IRQ 9", but it wasn't freed > by me > To: "nils.stec" <nils.stec(a)googlemail.com> > Cc: kernelnewbies <Kernelnewbies(a)kernelnewbies.org> > Message-ID: > <CA%2BfM3Xy2QALrjbTYJxW0yKn-Q-Y99Wi8xUyyWtKEzYDTByTkjQ(a)mail.gmail.com > > > Content-Type: text/plain; charset="iso-8859-1" > > Hi Nils, > > >>void cleanup_module(void) { > >> ... > >> free_irq(ADC_IRQ, NULL); /* remove interrupt handler */ > >> ... > >> return; > >>} > > You should not pass NULL here. It should be the unique cookie that you > passed in request_irq (adc_irq_handler in your case) since you have used > IRQF_SHARED which means you want to share your interrupt line. Also check > whether you really want to share your interrupt line and also if you want > to use "(void *)(adc_irq_handler)" as the unique identification. > > HTH! > > Regards > Mayur > > On Tue, Feb 7, 2012 at 7:45 PM, nils.stec <nils.stec(a)googlemail.com> > wrote: > > > Hi, > > > > atm I'm writing a kernel module for an embedded ARM device. > > This module uses IRQ9. > > > > If i remove the module, the kernel tells me that: > > > > ------------[ cut here ]------------ > > WARNING: at kernel/irq/manage.c:858 __free_irq+0x84/0x154() > > Trying to free already-free IRQ 9 > > Modules linked in: adc_demo_irq(P-) g_ether pegasus mii > > [<c0028794>] (unwind_backtrace+0x0/0xd0) from [<c003b504>] > > (warn_slowpath_common+0x48/0x60) > > [<c003b504>] (warn_slowpath_common+0x48/0x60) from [<c003b554>] > > (warn_slowpath_fmt+0x24/0x30) > > [<c003b554>] (warn_slowpath_fmt+0x24/0x30) from [<c005fa00>] > > (__free_irq+0x84/0x154) > > [<c005fa00>] (__free_irq+0x84/0x154) from [<c005fb0c>] > > (free_irq+0x3c/0x5c) > > [<c005fb0c>] (free_irq+0x3c/0x5c) from [<bf01e18c>] > > (cleanup_module+0x4c/0x60 [adc_demo_irq]) > > [<bf01e18c>] (cleanup_module+0x4c/0x60 [adc_demo_irq]) from [<c005b898>] > > (sys_delete_module+0x1c4/0x238) > > [<c005b898>] (sys_delete_module+0x1c4/0x238) from [<c0022dc0>] > > (ret_fast_syscall+0x0/0x28) > > ---[ end trace 60d7a16d878ac0b3 ]--- > > adc testing module removed > > ------------[ cut here ]------------ > > > > The message "adc testing module removed" comes from my module > **after**free_irq() via printk, so the module exit routine works till the > end. > > > > This is my code (only the IRQ related part): > > > > irqreturn_t adc_irq_handler(int irq, void *dev_id) { > > > > ... do someting ... > > > > return IRQ_HANDLED; > > } > > > > int init_module(void) { > > int32_t retval; > > ... > > retval = request_irq(ADC_IRQ, adc_irq_handler, IRQF_SHARED, "lpc313x > > adc irq", (void *)(adc_irq_handler)); > > ... > > return retval; > > } > > > > void cleanup_module(void) { > > ... > > free_irq(ADC_IRQ, NULL); /* remove interrupt handler */ > > ... > > return; > > } > > > > > > I hope anyone of you can help me with that problem. If you need more > > information, i'll send it > > > > Greetings, > > Nils > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > > >

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parent inode from the current struct inode
by Jack David Feb. 8, 2012

Feb. 8, 2012

Hi All, Is possible to get parent directory's inode structure from the current inode? If so, how can I do that? Also, is it possible to get the "struct file" if we have "struct inode" ?? Thanks, J

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