September 2015 - 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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kernel.c//Starting for The Journey of The Kernel;
by GanesH AvacharE Sept. 17, 2015

Sept. 17, 2015

#include <Hello Everyone>, I am Ganesh, I am New Here, I want to Learn the Kernel Code , How Kernel Handles the all the things?, Each and Everything Real Mysteries of the Kernel, So Please Help me, From where should I start, What Sequence Should I Follow to get Started with Kernel. Please Help me Guys and Have a NICE Day. return Thank you; Regards, Ganesh Avachare

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git sendmail configuration example for mail.reiseup
by Dario Sept. 17, 2015

Sept. 17, 2015

Hi All, i'm trying to use mail.reiseup.net with git sendmail. my configuration of git is: [sendemail] smtpEncryption = ssl smtpServer = reiseup.net smtpUser = USER(a)reiseup.net smtpServerPort = 465 smtppass = MYSECRETPASS At the moment i get the error "unable to initialize SMTP properly. Check config and use --smtp-debug " I'm on opensuse and i have postfix al mua. I use Mutt with imap and i don't have problems. I try the flag smtp-debug but i don't see any details for logging. Do have some hints? Thank you in advance Regards

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A Question about TCP Sequence rollover
by Ramana Reddy Sept. 16, 2015

Sept. 16, 2015

Hi All, I would like to the code where exactly the TCP sequence number rollover happens in the linux kernel. Thanks & regards, Ramana

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mmap - post/pre actions
by Ran Shalit Sept. 16, 2015

Sept. 16, 2015

Hello, I need to implement mmap for non-volatile memory chip (NVRAM). I already did something simple, but now I understand that it is not complete: The nvram need to be unlock and locked after finishing the memory task of read/write. Does mmap can handle such post/pre actions or not ( I guess that if not - I will need to use read/write alternatives) ? Thank you, Ran

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When to use threaded interrupts?
by Kosta Zertsekel Sept. 15, 2015

Sept. 15, 2015

Hi guys, I hope I'm on right mailing list. :-) I think I get the pro of using threaded interrupts - to decrease the maximum interrupt latency on RT workloads and/or RT machines (servers, embedded, etc.). Also, I see that in 4.2 there are only ~76 drivers that use threaded interrupt: ``` $ git grep -l IRQ_WAKE_THREAD | sort | grep -v "\.h" | wc -l 76 ``` So, I'd like to ask: - Why not **all** of the drivers use the threaded interrupts? - What are the cons of the threaded interrupts? Thanks, --- KostaZ

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Userspace pages in UC mode
by Sabela Ramos Garea Sept. 14, 2015

Sept. 14, 2015

Dear all, For research purposes I need some userspace memory pages to be in uncacheable mode. I am using two different Intel architectures (Sandy Bridge and Haswell) and two different kernels (2.6.32-358 and 3.19.0-28). The non-temporal stores from Intel assembly are not a valid solution so I am programming a kernel module that gets a set of pages from user space reserved with posix_memalign (get_user_pages) and then sets them as uncacheable (I have tried set_pages_uc and set_pages_array_uc). When I use one page, the access times are not very coherent and with more than one page the module crashes (in both architectures and both kernels). I wonder if I am using the correct approach or if I have to use kernel space pages in order to work with uncacheable memory. Or if I have to remap the memory. Just in case it makes it clearer, I am attaching the relevant lines of a kernel module function that should set the pages as uncacheable. (This function is the .write of a misc device; count is treated as the number of pages). Best and Thanks, Sabela. struct page *pages; //defined outside in order to be able to set them to WB in the release function. int numpages; static ssize_t setup_memory(struct file *filp, const char __user *buf, size_t count, loff_t * ppos) { int res; struct vm_area_struct *vmas; numpages = count/4096; down_read(&current->mm->mmap_sem); res = get_user_pages(current, current->mm, (unsigned long) buf, numpages, /* Number of pages */ 0, /* Do want to write into it */ 1, /* do force */ &pages, &vmas); up_read(&current->mm->mmap_sem); numpages=res; if (res > 0) { set_pages_uc(pages, numpages); /* Uncached */ printk("Write: %d pages set as uncacheable\n",numpages); } else{ pr_err("Couldn't get pages to set them as UC :(\n"); return -EAGAIN; } }

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gfp_flag
by Ronit Halder Sept. 14, 2015

Sept. 14, 2015

In drivers/staging/android/ion/ion.c in line 1475 and 1493 gfp_flag is set to -1 what are these lines doing? regards, Ronit

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Re: Advice on Linux Kernel Development
by Abhishek bist Sept. 14, 2015

Sept. 14, 2015

Hi , It is generally recoomended to not to do the kernel development with virtual box and especially dealing with the device drivers. On 14 September 2015 at 09:37, Mayur Patil <linuxcraz23(a)gmail.com> wrote: > [image: Boxbe] <https://www.boxbe.com/overview> This message is eligible > for Automatic Cleanup! (linuxcraz23(a)gmail.com) Add cleanup rule > <https://www.boxbe.com/popup?url=https%3A%2F%2Fwww.boxbe.com%2Fcleanup%3Ftok…> > | More info > <http://blog.boxbe.com/general/boxbe-automatic-cleanup?tc_serial=22630835134…> > > Hi, > > I am using Reliance 3 (Netconnect+) Dongle......and with lots of tries, I > have finally stopped trying to install it on CentOS 6.x. > > I have tried almost all instructions from posts and blogs which appears on > first 2 pages of Google search. > > > On Mon, Sep 14, 2015 at 8:57 AM, Karthik Nayak <karthik.188(a)gmail.com> > wrote: > >> On Sun, Sep 13, 2015 at 11:40 PM, Mayur Patil <linuxcraz23(a)gmail.com> >> wrote: >> > hi all, >> > >> > I want to ask >> > >> > if I want to get started with Linux Kernel Development then is it >> feasible >> > that >> > >> > I can do all my experiments on Virtual Machine as on Linux my Internet >> > dongle does >> > >> > not work, I am asking in terms of performance and efficiency. >> > >> >> Just curious, which dongle do you use? and what did you try? >> >> > Looking for guidance, >> > >> > Thanks ! >> > -- > > > *-- * > *Mayur S Patil,* > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > >

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Advice on Linux Kernel Development
by Mayur Patil Sept. 14, 2015

Sept. 14, 2015

hi all, I want to ask if I want to get started with Linux Kernel Development then is it feasible that I can do all my experiments on Virtual Machine as on Linux my Internet dongle does not work, I am asking in terms of performance and efficiency. Looking for guidance, Thanks ! -- *Mayur S Patil,*

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