November 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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serial: 8250: RX hang issue
by Pradeep Kumar Jan. 25, 2012

Jan. 25, 2012

Hi All, I am working on a mobile development platform and performing some stress warm boot tests using UART debug console(which is using serial 8250 driver for console). I am getting device debug console UART RX hang after iterations > 1500. after this issue am not* able to issue any command. Able to see logs though. Later I kept some debug prints in isr and able to see that device is able to generate interrupts when some data is received. So I came to conclusion that some malfunctioning is happening in upper layer not sure which layer has this problem. Can some one give some ideas at which layer I can check? One more observation is when I perform a open and close calls on debug UART port(in my case ttyS0) while device is in UART RX hang state, then I notice the UART console RX again below active and able issue commands from UART console itself.

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Filtering USB storage data in kernel module
by Abhijit Pawar Jan. 12, 2012

Jan. 12, 2012

Hi All, I need to filter the data written/read to and from the USB storage disk. Now the way USB is made known to OS is through SCSI and then respective filesystem ( mostly usbfs). So is there any way I can intercept this stack and have my kernel module invoked so that I will get the data. I have been thinking on two approaches: 1. Use VFS and write a proxy filesystem for USB device which will filter the data. 2. checking SCSI and any intercepting point. I am currently looking at USBMONITOR source code as well. Please let me know if there is any other way to achieve this. Regards, Abhijit Pawar

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Is there a way to build a cross reference with kernel file
by Jimmy Pan Dec. 18, 2011

Dec. 18, 2011

It seems we can use ctags, while, I don't really know how to implement it. I don't want to use the online cross reference every time... Thanks.

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Guidance on writing device drivers
by suraj khurana Dec. 15, 2011

Dec. 15, 2011

Hi all, I am a newbie in linux world and want to learn linux device drivers. I am currently reading book - "Linux Device Drivers" by O'reilly. Does anyone has any problem statements based on device drivers for practice so that I can enhance my skills in writing device drivers. Thanks, Suraj

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Queries about Net-Filter Hooks !!!
by Kesava Srinivas Dec. 11, 2011

Dec. 11, 2011

HI Friends, Trying to Play with Net-Filter Hooks and here are my Queries! 1] While adding a New UDP/IP Header over the received skbuffer from NetFilter Module;need to fill the UDP Check-sum. Please let me know ; if there is any Kernel Function which we can use to do this Job ??? OR Do I need to write our own Function to calculate the Check-sum ??? 2] Once after adding New Headers to the received skbuffer ; am trying to return NF_ACCEPT. My Understanding was that ; the newly expanded skbuffer with added Headers will be again taken my Net-Filter Hooks Module and will deliver back to the net device. rt? OR Was there some thing more that I should do ; to send the new skbuffer to the device ?? Looking forward for the reply !! -Thanks in Advance, VKS

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VFAT i_pos value
by Kai Meyer Dec. 9, 2011

Dec. 9, 2011

I'm getting this error: FAT: Filesystem error (dev sblsnap0) fat_get_cluster: invalid cluster chain (i_pos 523791) I'm wondering if there was a way to figure out what sector is causing the error? I would like to try and track down what is changing that sector and fix the problem. Is there a straight forward way to convert i_pos to a sector value? I've been staring at the fat.c and fat.h code all morning, and I'm having trouble grok'ing the flow. -Kai Meyer

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contribute to linux kernel
by Mayank Agarwal Dec. 2, 2011

Dec. 2, 2011

Hi all, I have just joined the kernelnewbies.I want to contribute to linux kernel or to any of the open source ongoing projects.Has good experience in c,c++ and linux programming. Please suggest how can i go about that. Regards, Mayank

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What is the purpose of parse_elf() in misc.c
by Graeme Russ Dec. 2, 2011

Dec. 2, 2011

Hi All, In looking at booting a raw x86 kernel image, I discovered that the compressed image in bzImage is actually an ELF image created with: objcopy -R .comment -S vmlinux After decompressing the image, the parse_elf() function in misc.c copies the sections from the ELF image (there are 3 sections, only 2 are marked PT_LOAD) into their final resting place in memory. This got me to thinking, why not use: objcopy -O binary -R .comment -S vmlinux I wrote a little stand-alone parse_elf() program, and lo-and-behold, the outputs are identical. So, in theory, if bzImage contained a raw binary, it could be decompressed directly to the target address. Now there is some adjustment in parse_elf() for relocatable kernels, but I can't but think that this could be simply catered for in the decompression target address Surely this would speed up kernel loading by removing the additional copy that parse_elf() introduces Or am I missing something significant? Regards, Graeme

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modify bootlog in linux
by Mayank Agarwal Dec. 1, 2011

Dec. 1, 2011

Hi, I am trying to learn linux.I have following doubts: 1.In which files/directory we initialize bootlog.which files i have to change in order to modify boot log. how to make a process run as daemon process. 2.Also about linux boot sequence,help/tutorial on linux boot sequence. 3.Major steps in bringing up the new custom evm board. 4.Things to know in order to write the bootloader. Thanks and Regards, Mayank

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