July 2012 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

NFS - changing IP address after startup
by Ran Shalit July 7, 2012

July 7, 2012

Hello, Is it legal to change ip address & mac address when working with NFS, and after linux finished startup ? It seems that in such case, NFS can get stuck, right? Thank you, Ran

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Syscalls: When can I use "cond_syscall()" macro?
by Gustavo da Silva July 6, 2012

July 6, 2012

Hello, friends!! How are you?! Im studing the linux kernel, to be part of the community!! Anyone know where/when can I use the con_syscall() macro?! And another question: Where are the file "unistd_32.h"?! I'm not founding it in the "arch/x86/include/asm/" directory!! []'s Peace. -- Atenciosamente, Gustavo da Silva gustavodasilva(a)gmail.com

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Just a test! I would like to someone reply this!
by Gustavo da Silva July 6, 2012

July 6, 2012

Hello Guys. Im just testing. Can someone just send a response, only to check if my e-mails are going to Kernelnewbies??!!! Thx in Advance! Peace. -- Atenciosamente, Gustavo da Silva gustavodasilva(a)gmail.com

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Need pointers for Bootloader
by siddharth saxena July 6, 2012

July 6, 2012

Hi I am going to start work on bootloader for ARM based OMAP SoCs. Have been reading about it. I have gathered the basics and now want to have a working understanding. Can anybody provide some pointers about some good sources or examples to study and practice? Regards Siddharth

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Why can not processes switch in atomic context?
by Parmenides July 5, 2012

July 5, 2012

Hi, It is said that kernel can not be preempted in interrupt context and when it is in a critical section protected by a spin lock. 1. For the spinlock case, it is easy to get if preemption is allowed in critical section, the purpose of protection provided by spinlock can not be achieved readily. 2. For the interrupt context case, I think when processing interrupt, kernel can be preempted in principle. But, this really increases the interrupt processing time which further cause longer response time and data missing in device. Except that, is there any other reasons? 3. Kernel is responsible for prohibiiting passive process switches, namely preemption, in the above cases. But, It seems that it does not take care of active process swtiches, namely yield. For example, some code in a critical section protected by a spinlock can invoke schedule() to switch process passively. Is this the case?

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Regarding Memory models
by sandeep kumar July 5, 2012

July 5, 2012

Hi all, While going through the Kernel memory management code, i came across the few configuration options. I would like to know more clearly about the following things. 1) What is FLAT MEMORY MODEL & SPARSE MEMORY MODEL & DISCONTIGEOUS memory? Which cases you use each of them 2) What is Memory hot plugging? and the relation between 1 & 2. Can u apply hotplugging feature to Flat/Sparse? -- With regards, Sandeep Kumar Anantapalli,

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Re: Why can not processes switch in atomic context?
by anish singh July 4, 2012

July 4, 2012

Always CC Kernelnewbies. On Wed, Jul 4, 2012 at 12:52 AM, Parmenides <mobile.parmenides(a)gmail.com> wrote: >>> 1. For the spinlock case, it is easy to get if preemption is allowed >>> in critical section, the purpose of protection provided by spinlock >>> can not be achieved readily. >> I don't know what you mean here.Please clarify. >>> > > Sorry, this is not a problem really. :-) A critical section protected > by a spinlock is atomic. So, preemption is prohibited when kernel > enter this kind of critical section. I just want make sure it is the > case. > > >>> 2. For the interrupt context case, I think when processing interrupt, >>> kernel can be preempted in principle. But, this really increases the >>> interrupt processing time which further cause longer response time and >>> data missing in device. Except that, is there any other reasons? >> data missing in device.Can you elaborate that? >> Stack space is pretty limited in ISR context.Does that give you a clue? >>> > > data missing: For example, if a interrupt sent by Ether card can not > processed for a long time, some frames received from the cable might > be discarded owing to its limit buffer on card. > Actually, every process has its kernel stack. If a preemption occurs > during interrupt processing, the stack of another process is used. So, > I think stack space is not a problem at all. https://lkml.org/lkml/2007/8/3/2 this thinks otherwise.Please read this as stack space is one of the reasons why sleeping is not allowed in ISR context. > > >>> 3. Kernel is responsible for prohibiiting passive process switches, >>> namely preemption, in the above cases. But, It seems that it does not >>> take care of active process swtiches, namely yield. For example, some >>> code in a critical section protected by a spinlock can invoke >>> schedule() to switch process passively. Is this the case? >> I don't understand this question but we don't switch when we are holding >> spinlock as that will jeopardize the integrity of the system i.e. >> suppose you slept while holding spinlock.What would happen? > > So, kernel maintains its integrity relying on that we don't yield > while in interrupt handler or critical section protected by a > spinlock. If we do so, kernel do nothing at all. Why doesn't it refuse > schedule when it finds out that we yield in a improper context. AFAIK it prints some kind of warning message.Why don't you try this? Call schedule in ISR context(try in threaded ISR) and share with us the results.

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NFS - client ip address
by Ran Shalit July 3, 2012

July 3, 2012

Hello, I would like to ask your advise concerning modifying ip address: I need to modify ip address and ethernet address according to some hardware input in application. This change can be done in u-boot or linux. When I consider where is the best place to set the ip/mac address ( u-boot or linux), I also take into account that I will work with NFS in debug stage. - Now, as far as I understand, If I will modify the ip/mac in linux instead of u-boot, it can be a problem when working with NFS, becuase NFS need constant ip address and ethernet address, right ? - Is it a problem to make this changes in linux if working with NFS or should it be done in u-boot only ? Thank you, Ran

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Re: kgdb over ethernet support for 3.x kernel
by Amit Nagal July 3, 2012

July 3, 2012

On Mon, Jul 2, 2012 at 10:35 PM, <Ashish_Bunkar(a)dell.com> wrote: > what i know is gdb over ethernet is removed from newer kernels. > Please let me know if you have some other information. > > Thanks > Ashish Bunkar > ________________________________________ > From: kernelnewbies-bounces(a)kernelnewbies.org [kernelnewbies-bounces(a)kernelnewbies.org] On Behalf Of Amit Nagal [helloin.amit(a)gmail.com] > Subject: kgdb over ethernet support for 3.x kernel > > Hi , > > 3.x kernel does not seem to have built in support to use kgdb over > ethernet functionality . > To use this , can i be guided from where i can download patch for the > same and apply to 3.x series kernel ? > > thanx & regards > Amit Nagal > Actually i want to to debug kernel modules with kgdb - gdb connected over tcp / udp port as depicted in http://kernel.org/pub/linux/kernel/people/jwessel/kdb/EnableKGDB.html section 3 . but in kernel , there seems to no built in support for that . Thanx & Regards Amit Nagal

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kgdb over ethernet support for 3.x kernel
by Amit Nagal July 2, 2012

July 2, 2012

Hi , 3.x kernel does not seem to have built in support to use kgdb over ethernet functionality . To use this , can i be guided from where i can download patch for the same and apply to 3.x series kernel ? thanx & regards Amit Nagal

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