January 2013 - kernelnewbies@kernelnewbies.org

bitops or mutex
by Prashant Shah Jan. 21, 2013

Jan. 21, 2013

Hi, There is a bitmap that needs to be locked across many threads for test / set bit operations. Which one is faster - bitops or mutex ? 1. Bitops : set_bit(5, (long unsigned *)&tmp); 2. Mutex : mutex_lock(&m); *tmp = (*tmp) | (1 << 5); mutex_unlock(&m); Regards.

2 1

How does __user works?
by Grzegorz Dwornicki Jan. 21, 2013

Jan. 21, 2013

How does __user macro works? I know it is defined in include/linux/compiler.h as: # define __user. __attribute__((noderef, address_space(1))) I could write thesse macros defs too but my real problem is: what does this stuff do? Some functions use this macro and other does not. For example compat_do_execve (from include/linux/comtap.h) use normal pointer named filename and second pointer named argv as __user pointer. Why does argv needs __user but filename not? Gregory

3 2

how to get outsated mail ?
by horseriver Jan. 21, 2013

Jan. 21, 2013

hi: If I subscribed a mail list at date x , how can I get those mail dated before x ? can I request maillist server to send those mail to my mail address ? thanks!

3 3

File system development question
by Racz Zoltan Jan. 21, 2013

Jan. 21, 2013

Hi. Some days ago I started studying the linux VFS api, and until now I wrote a mountable only file system. I would like to go further than that, but I didn`t find any good documentations on google. Some of them are incomplete, others are written for the 2.4 kernel series etc. Can somebody recommend a good book or documentation about file system development on the 2.6 or 3.x kernel series? It`s not a problem if it doesn`t contain a full source code (I don`t want to only copy paste code written by someone else, compile it, and voila, I`m a kernel developer). Reading the vfs api,or source files from the kernel is fine, but without knowing step by step what do I need to do, I only end up with kernel panics, and it is really hard to figure out what happened. Thank you.

2 1

Need for .rel.text in vmlinux!
by sebas sujeen Jan. 21, 2013

Jan. 21, 2013

Hello, I was just verifying the sections in vmlinux file, I am just thinking why there is a .rel.text or more generally relocation sections in a vmlinux file. If it is relocatable , then does it not require a linker of some sort to fix the relocation symbols? Thanks in advance! Best regards, -sujeen

1 0

no error thrown with exit(0) in the child process of vfork()
by Niroj Pokhrel Jan. 19, 2013

Jan. 19, 2013

Hi all, I have been trying to create a process using vfork(). And both of the child and the parent process execute it in the same address space. So, if I execute exit(0) in the child process, it should throw some error right. Since the execution is happening in child process first and if I release all the resources by using exit(0) in the child process then parent should be deprived of the resources and should throw some errors right ?? In the following code, however the process ran fine even though I have exit(0) in the child process ........ #include<stdio.h> #include<stdlib.h> #include<sys/types.h> #include<unistd.h> int main() { int val,i=0; val=vfork(); if(val==0) { printf("\nI am a child process.\n"); printf(" %d ",i++); exit(0); } else { printf("\nI am a parent process.\n"); printf(" %d ",i); } return 0; } // The program is running fine ..... But as I have read it should throw some error right ?? I don't know what I am missing . Please point out the point I'm missing. Thanking you in advance.

4 6

Where this come out?
by horseriver Jan. 19, 2013

Jan. 19, 2013

hi: I am linking a .so from one .o file with my specified linker script. In this linker script file , I do not use SIZEOF_HEADERS,but ld still report this error : Not enough room for program headers, try linking with -N I really can not understand . Any advice is appreciated ! Thanks!

2 2

socket state after accept() return
by horseriver Jan. 19, 2013

Jan. 19, 2013

hi: For one socket , which has been returned by accept() call , does its sk_state is assuredly already TCPF_ESTABLISHED ? thanks!

2 1

Help in pid_task()
by sebas sujeen Jan. 19, 2013

Jan. 19, 2013

hey guys, i am having a small doubt in "pid_task" function in kernel/pid.c.. Assume if the type is PIDTYPE_PGID, then it means that there are multiple processes associated with the process group and each has its own task_struct..so how come the function returns the task_struct of the "head" element of the hlist_node? Sorry if my assumptions are wrong! Thanks in advance

1 0

How to wake_up the wait_queue of a socket?
by horseriver Jan. 19, 2013

Jan. 19, 2013

hi: When one datagram has reached , How to wake_up the wait_queue of that socket ? Thanks!

3 5