September 2011 - kernelnewbies@kernelnewbies.org

Changes in block layer for IOScheduler Insertion selection
by mani Feb. 6, 2012

Feb. 6, 2012

Dear All, I am working on linux kernel 2.6.32.9 tegra NVIDIA board. I am getting ~8MBps speed of the Nand disk if i use hdparm hdparm -t /dev/mtdblock3 i made changes in block layer of kernel as below:- block/blk-core.c static inline void add_request(struct request_queue *q, struct request *req) { drive_stat_acct(req, 1); /* * elevator indicated where it wants this request to be * inserted at elevator_merge time */ __elv_add_request(q, req, ELEVATOR_INSERT_BACK, 0); //__elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0); } changed ELEVATOR_INSERT_SORT to ELEVATOR_INSERT_BACK it improves my NAND speed to 10MBps. I am using "noop" I/O scheduler. Will this change have any adverse effect in kernel ? or any other side effect as far as i am using only Nand no Hard disk. Thanks Mani

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Purpose of using __be16 inside a data structure?
by 陳國成 Oct. 25, 2011

Oct. 25, 2011

Hi all, Please tell me the difference between using unsigned short and __be16 to declear a variable in a data structure. For example, in include/net/inet_sock.h, struct inet_sock is decleared as struct inet_sock { __be16 inet_dport; }; not struct inet_sock { unsigned short inet_dport; }; I think it has something to do with endianness. But I see that both __le16 and __be16 are unsigned short when using gcc with -E option for little-endian and big-endian platform. Can someone give me more information? * little-endian typedef unsigned short __u16; typedef __u16 __le16; typedef __u16 __be16; * big-endian typedef unsigned short __u16; typedef __u16 __le16; typedef __u16 __be16; Regards, GC

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File change notification along with user
by V.Ravikumar Oct. 12, 2011

Oct. 12, 2011

Hi all, Is it possible to write a module/driver which notifies file/directory change asynchronously along with user name(or with uid) who modified it. inotify will do change notification but it will not provide uid who modified/created the file. audit and inotify combination can work, but I'm looking for a better option than this. Please help me. Thanks, Ravi

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userspace address to bus address
by Florian Bauer Oct. 10, 2011

Oct. 10, 2011

Hi, I'm currently writing my first kernel module, but i got stuck with address translations. I want my pcie device to access a buffer which was allocated in userspace (page aligned, currently smaller than one page to ignore scattering). I tried to translate the userspace address to a bus address in my ioctrl handler like this: void __user *data = arg; down_read(&current->mm->mmap_sem); get_user_pages(current, current->mm, (unsigned long)data, len/*1*/, 1, 0, &pages, NULL); up_read(&current->mm->mmap_sem); void* kvaddr = kmap(pages[0]); unsigned long baddr = virt_to_bus(kaddr); kunmap(pages[0]); page_cache_release(pages[0]); //... data is page-aligned and was locked in userspace with mlock. There is some address in baddr, but the device does not write to the correct location and sometimes causes kernel freezes. Can someone tell me, what is wrong with this code?TheI device works with a address, that was received in different way (closed source driver). I use 32 bit Ubuntu with an 2.6.32 kernel.

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Enabling USB OTG
by madav maddy Oct. 10, 2011

Oct. 10, 2011

Hi Experts, I am newbie and trying to enable usb OTG support in Android linux kernel, can someone please give me the pointers to proceed with this. The hardware on which android kernel boots has OTG harware, so inorder to enable it at the kenel level i enabled the following configs, CONFIG_USB_SUPPORT=y CONFIG_USB_ARCH_HAS_HCD=y CONFIG_USB_ARCH_HAS_OHCI=y CONFIG_USB_ARCH_HAS_EHCI=y CONFIG_USB=y CONFIG_USB_DEBUG=y . . CONFIG_USB_EHCI_HCD=m CONFIG_USB_OHCI_HCD=m . . CONFIG_USB_OTG=y CONFIG_USB_MUSB_OTG=y CONFIG_USB_OTG_UTILS=y am using the following configuration, musb <--- usb converter <--- usb harware device. But still the hardware doesnt seems to work properly (as no new entry is created in /dev, when a usb harware device is connected to the board), Inorder to confirm that the base board drivers are working properly, i tried loading the gadget driver and connected it to the PC host, where i was able to access the device mass storage successfully. Do i need to do anything else to enable the musb to work as OTG port. Thanks, Madavan

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Why do processes with higher priority to be allocated more timeslice?
by Parmenides Oct. 7, 2011

Oct. 7, 2011

Hi, It seems that Linux's scheduler tends to allocate longer timeslice for processes with higher priority. Actually, the CFS scheduler which is a new scheduler in Linux kernel also does the same thing. But, I think this way does not fit with scheduler's principle. The goal chased by a scheduler is low latency and high thoughput. Normally, a I/O-bound process has higher priority, while a CPU-bound process has lower priority. So, a I/O-bound process (which has enough timeslice) can preempt a CPU-bound process easily. This way ensures lower latency. It is also necessary that CPU-bound processes are to be allocated longer timeslice to improve throughput owing to less process switch costs. That means lower priority processes (CPU-bound) should be allocated longer timeslice, whichs obviously conflicts with the actual practice taken by the Linux's scheduler. Any explanation? Thanks.

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Getting dirtied pages info
by Prateek Sharma Oct. 3, 2011

Oct. 3, 2011

Hi all, What would be a good way to get a list of all pages(lets say pfns) dirtied in a particular time interval ? I am reading about MMU_notifiers but i think a simpler, light-weight solution might work.. I came across the page-dirtied bits...are those saved somewhere by the kernel on context-switches? Thanks!

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Backtrace Call Stack
by Harish G. Naik Oct. 2, 2011

Oct. 2, 2011

Hi, I have been trying to get some debug information from a point in the kernel where I am seeing some errors. I am actually trying to figure out how a particular point in code was reached. Here is what I did: if (case_when_error_happens) { extern int sprint_symbol(char *buffer, unsigned long address); for (i = 0; i < depth; i++) sprint_symbol(bt[i], (unsigned long)__builtin_return_address(i)); printk("%s < %s ...", bt[0], bt[1] ...); } I get most of the information I want. But I was wondering if there was any other cleaner, more straight forward way to do this. Thanks. -Harish

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regarding disable of CONFIG_DEBUG_FS
by Amit Nagal Sept. 30, 2011

Sept. 30, 2011

Hi , i want to disable CONFIG_DEBUG_FS in my kernel configuration . i am using 2.6.35 kernel on a embedded arm target . i am using usb hid driver to fetch thumbnail data on usb hid interface . the reason why i want to disable CONFIG_DEBUG_FS is that in interrupt callback , i dont want to spend time in debugging functions which are enabled with CONFIG_DEBUG_FS . can i be guided how to do that ? its not possible to do using make menuconfig though . Regards Amit Nagal

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What is "__attribute__()" in kernel code
by sandeep kumar Sept. 30, 2011

Sept. 30, 2011

Hi all, I was wondering what __attribute__ does in the kernel code? I found several definitions but couldnot come to one conclusion.. __releases(x) is defined in compiler.h. What does this mean?? # define __releases(x) __attribute__((context(x,1,0))) Thanking you -- With regards, Sandeep Kumar Anantapalli,

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