- kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

why no vsyscall support on x86 or i386 ?
by Fredrick Dec. 16, 2011

Dec. 16, 2011

Hi, Why there is no vsyscall support on i386? I see it only on x86_64. In x86_64 it supports gettimeofday, etc. In i386, it only uses to support the sysenter optimization. Why there is no support for gettimeofday in i386 as a vsyscall? -Fredrick

1 0

Why is the xadd instruction used to get atomic operation?
by Parmenides Dec. 15, 2011

Dec. 15, 2011

Hi, xadd is used in atomic function atomic_add_return() like this: 188static __inline__ int atomic_add_return(int i, atomic_t *v) 189{ 190 int __i; ... ... ... 195 /* Modern 486+ processor */ 196 __i = i; 197 __asm__ __volatile__( 198 LOCK "xaddl %0, %1;" 199 :"=r"(i) 200 :"m"(v->counter), "0"(i)); 201 return i + __i; 202 ... ... ... 211} The xadd will store v->counter into i, and store v->counter+i into v->counter. I wonder why we bother to obtain v->counter atomically. I try to modify the asm with the following code: static __inline__ int atomic_add_return(int i, atomic_t *v) { __asm__ __volatile__( LOCK "addl %1, %0;" : "m"(v->counter) : "=r"(i), "m"(v->counter)); return v->counter; } Does my code may cause some problems concerning atomic operation?

2 1

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

6 5

interrupt handler in arm question
by subin gangadharan Dec. 14, 2011

Dec. 14, 2011

Hi All, I am trying to understand how the interrupt handler in arm working.By looking at the code,what I understood,when an interrupt happens arm disables the irq, saves the cpsr to spsr,save current pc to lr and switches to irq mode. So in case of interrupt it branches to the vector_irq and there it saves some registers and depending on which context its happened,it will call __irq_user or __irq_svc.But before that it switches to the supervisory mode. Here I got confused,because in this case user registered handler will be executed in supervisory mode. I was thinking interrupt handler will always be executed in interrupt mode. Could any one please give some pointers on this. -- With Regards Subin Gangadharan I am not afraid and I am also not afraid of being afraid.

2 8

How to copy kernel headers?
by autif khan Dec. 14, 2011

Dec. 14, 2011

I have linux kernel source in a directory (say) /home/autif/linux-2.6.29.4 I can make xconfig followed by make bzImage, followed by make modules Now, I can install the modules using "make modules_install INSTALL_MOD_PATH=/home/autif/2.6.29.4.modules" - This works beautifully, without any issue. I have tried to install the kernel headers using "make headers_install INSTALL_HDR_PATH=/home/autif/2.6.29.4.headers" I can tar and extract these modules and headers on some other computer (target computer) at the right location. Meaning that modules are extracted to /lib/modules/2.6.29.4/ and "build" is symlinked to /usr/src/linux-headers-2.6.29.4 - where I extracted the headers. However, I only get the include directory. When I try to build a driver on the target computer, there is complaint that I do not have a Makefile in /usr/src/linux-headers-2.6.29.4 The build produces something like 1.5 GB of files and this is too much for my target system. I am reluctant to build the driver on the build system and want to build it on target. Both build and target are i386 systems (one a full blown Debian based), the other something somewhat based on LFS. So, my short problem is - what make command I need to execute to install the build dependencies (including headers, Makefiles and other stuff that may be required by the driver) to copy that stuff over to a custom directory (say /home/autif/2.6.29.4.build_dependencies) so that I can tar it up and extract is on my target system at (say) /usr/src/linux-2.6.29.4 Thanks Autif

3 4

Storage and I/O subsystem
by RKK Dec. 14, 2011

Dec. 14, 2011

Hello all, I want to start learning the Linux Block I/O stack about how it handles I/O requests and about the storage subsystem .anybody has any documents with that ? any pointers for where to start ? and how to start? thanks. -- Warm Regards, Ravi . "I don't Know is not a excuse , its an opportunity to know."

2 1

cuboot/cuImage? treeboot/treeImage?
by Fredrick Dec. 14, 2011

Dec. 14, 2011

Hi, I was looking at the different powerpc bootable images. What are these 'cuImage' and 'treeImage'? Could someone explain when these images are used? Thanks, Fredrick

2 2

Learning Linux Kernel
by Kaushal Shriyan Dec. 13, 2011

Dec. 13, 2011

Hi I have been working on Linux OS for the last 10 years and it has been very exiting and challenging to learn new technologies based on Linux. I am basically a Sys Admin for Linux with bash programming and configuring and setting up Linux Server including network services like BIND DNS,Apache etc... Although i do not know C and ASM Language, I am very much eager to start learning Linux Kernel Code and contribute to linux kernel codebase sometimes down the line. Please guide/suggest me. Regards, Kaushal

8 10

how can we wake up some process which is scheduled?
by loody Dec. 13, 2011

Dec. 13, 2011

hi all: There is a kernel API, "schedule_timeout_interruptible". since it has the name interruptible, who and how can we interrupt this task? suppose A use schedule_timeout_interruptible for 20s period and B found something and he want to wake up A within this 20s period. -- Regards,

3 2

apply_alternatives and cpu hotplug
by Dannie Stanley Dec. 13, 2011

Dec. 13, 2011

Regarding kernel version 2.6.38.8. When a module is loaded apply_alternatives() is called which patches the module code with instructions from the ELF headers of the module. It is my understanding that these instructions are generally CPU optimizations based on the capabilities of the CPU. However, I notice that native_cpu_up() does not call apply_alternatives(). So is it assumed that the CPU capabilities will not change on CPU hotplug? Thank you, Dannie -- Dannie M. Stanley

1 0