January 2011 - kernelnewbies@kernelnewbies.org

Casting sock to inet_timewait_sock
by Daniel Baluta Jan. 14, 2011

Jan. 14, 2011

Hello, When casting sock to inet_timewait_sock ([1]) it is assumed that sock points to a structure of type inet_timewait_sock. Is there a way to check if a sock struct wraps around a inet_timewait_sock struct? thanks, Daniel. [1] http://lxr.linux.no/linux+v2.6.37/include/net/inet_timewait_sock.h#L189

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Nice Linux Reference Stuff
by Ashok Babu Jan. 14, 2011

Jan. 14, 2011

Hi Pals, For those who are new to linux kernel or need instant reference on various areas of linux, the following link would be a good start : http://www.makelinux.net/reference Thanks & Regards Ashok

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How to design protocol stack with can-bus driver of character driver
by cheng chen Jan. 14, 2011

Jan. 14, 2011

Hi all, I am working on vehicle body control system with can-bus as my BE final project. It contains three parts. 1.CAN chip driver 2.CAN-bus protocol stack 3.UI The problem is that I already have written the CAN chip driver as a character device driver using IO-simulated SPI. So with this character driver API open() read() write() ioctl(), I start to wonder where can I put my protocol stack? Or should rewrite the driver in network device frameworks? Thx -- Cheng(誠) Fedora Project Contributor -- Ambassador https://fedoraproject.org/wiki/User:Freakrobot _______________________________________________ My Page: http://freakrobot.blogbus.com/

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how to find the pointer address
by mohit verma Jan. 13, 2011

Jan. 13, 2011

hi all, i have to trap some kernel functions like: any pathname resolution function has to go through the link_path_walk() kernel function. so what this function returns is 0 on success or error. but when it reurns with 0 , the nameidata->dentry and mnt fields of nameidata structure point to the pathname component. so most probably( m not sure) this will change the stack address and get back to the calling point of link_path_walk(). is there any way by which i can find out the address of the pointer returned back from link_path_walk() (indirectly) of nameidata structure. i mean as u guys suggested me over here to just use kprobe() kernel tracing funtion to use but the problem is with how to find it out? is there any way in /proc subsystem to check it out? -- ........................ *MOHIT VERMA*

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Traversing Runqueu - CFS
by Jestin Joy Jan. 13, 2011

Jan. 13, 2011

Hi, Looking for a way to traverse the runqueue, so that I could get the contents of the runqueue. Initial reading tells that sched.h has ched_entity structure, which holds some of the data for it, like the struct rb_node run_node; Also read that redblack tree is used to hold the elements with "vruntime" as the index of it. Could anyone give a way forward to doing this.

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New proc entry under /proc/[pid]
by Mauro Romano Trajber Jan. 12, 2011

Jan. 12, 2011

How can I create a new proc entry under /proc/[pid] ? I using create_proc_entry("SOME_FILE", 0644, NULL /* here goes the pid proc entry */); Is there any way to get PID directory as a parent proc entry ? How ? Thanks, Mauro

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vfs functions
by mohit verma Jan. 12, 2011

Jan. 12, 2011

hi folks, i am confused with the functions starting from vfs_ . i think they show the significance of VFS model i mean if something could be done without touching the disk stuff then why not to do that but i am not quite sure. so please help me understand what does these actually mean?? thanks in advance guysss -- ........................ *MOHIT VERMA*

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syscall trace at kernel land
by mohit verma Jan. 12, 2011

Jan. 12, 2011

hi , let me explain myself : for example , open syscall calls sys_open then do_sys_open so like: do_sys_open -> do_filp_open -> link_path_walk -> so on. so while the cpu is executing the link_path_walk , is there any procedure in kernel to check for the interrupt vector number which caused it to be invoked? i mean like one of my friends said that when kernel is about to restart a syscall then it raises signal -ERESTARTSYS signal for signal handler. but i think it is for something went wrong and kernel wanna start the syscall again. but in between a syscall routine is it possible to get vector number (i repeat ,sorry) ?? thanks in advance for help -- ........................ *MOHIT VERMA*

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Question on mmap / expecting more calls to vfs_read
by Sebastian Pipping Jan. 12, 2011

Jan. 12, 2011

Hello! Intro / context =============== I'm trying to get a precise list of file names, offsets and byte counts of all read and write operations. I need that information to feed it into a simulator I am working on. I am running qemu-kvm with a slightly patched Linux kernel (additions of calls to printk only) sucking the kernel log from the serial console (kernel option earlyprintk=serial,keep) to a file. The setup itself works okay for me. Question / problem ================== When analyzing the kernel logs I produced I noticed stumbled over the case of a few libraries where only the beginning of the file (maybe its ELF header) was read repeated times, but nothing after: file /lib/ld-2.11.2.so max offset+count 456 total bytes read ever 502840 Especially as libc is among them, I guess some reads pass by me somehow. Any ideas what is shoveling the file bytes around? I found calls to do_mmap_pgoff for these file, though. That's when I thought I may need help understanding how mmap works. Is data read into the mapped region instantly all at once? Or is it feed into it on demand when the kernel gets read requests to a mapped area? In either case, where does the data come from if neither vfs_read nor do_readv_writev are ever called on the rest of the file? Thanks in advance for any help. Sebastian

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compiler error in simple module
by Hanumant Singh Jan. 11, 2011

Jan. 11, 2011

Hi I am trying to write a simple module that sort of emulates the ps command. I am trying to get the comm string for the task, using get_task_comm, but the make command keeps telling me that the symbol get_task_comm is not defined. I have included linux/sched.h. This is the header file, which I believe has the prototype definition for the function. Am I missing something? Thanks Hanumant

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