April 2015 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Basic question about malloc
by 慕冬亮 April 23, 2015

April 23, 2015

Hi, I'm looking for that whether the object allocated by malloc is the multiple of certain bytes! Or how does the malloc allocate dynamic memory ?? I does an experiment in my computer! #include<stdio.h> #include<stdlib.h> #define NUM 33 int main(int argc,const char *argv[]) { char *a, *b, *c; a = malloc(NUM); b = malloc(NUM); c = malloc(NUM); printf("a = %x\n",a); printf("b = %x\n",b); printf("c = %x\n",c); free(a); free(b); free(c); return 0; } But the result has no feature about a ,b ,c! Can someone tell me what's wrong with me? My GCC version is gcc (Debian 4.9.2-10) 4.9.2 mudongliang

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Re: Reusable Memory Manager
by nick April 23, 2015

April 23, 2015

On 2015-04-22 10:47 PM, Kenneth Adam Miller wrote: > On Wed, Apr 22, 2015 at 10:42 PM, nick <xerofoify(a)gmail.com> wrote: > >> >> >> On 2015-04-22 10:39 PM, Kenneth Adam Miller wrote: >>> So, I have a particular use case that has a lot to do with security. >>> >>> Basically, we have a intended secure kernel version with grsecurity and >>> other patches on it, and we have a specific application that has to do >> data >>> filtering as an inline reference monitor. >>> >>> The problem is, there is throughput and design considerations that are >>> limiting efficiency in the sense that it is highly difficult to make the >>> system concurrent and also highly difficult to scale-all while also being >>> secure. >>> >>> Basically, the memory regions have to be encoded at compile time because >> of >>> the way kernel segregation works. This makes the security proof of the >>> system far more simple and manageable; it's easy to say that no userland >>> monitor which is being given access to a specific memory region can >> access >>> outside of the region to which it is allocated, because it's statically >>> set. The tradeoff here is pretty severe, because the static settings that >>> have to be adopted pretty much mean that each particular monitor is >> given a >>> specific memory region; if there's a lot of traffic to a specific monitor >>> type, then that one type will be overwhelmed, but not even at the rate >> that >>> the machine itself could support. This is because all the other cores are >>> potentially sitting unused while the one in this worst case scenario is >>> running out of memory and not able to dispatch work to more cores. >>> >>> So my ultimate question is: is there some reusable, dynamic memory >>> allocation manager that can be used? I'm thinking that there has to, at >> the >>> least, be the constructs by which user land processes are managed and >>> divvied memory by the kernel itself. Does anybody know where that source >>> would be? Where I can go in order to learn more about that? >>> >>> What we want is a secure way to dynamically allocate memory from these >>> static memory page boundaries such that >>> >>> >>> >>> _______________________________________________ >>> Kernelnewbies mailing list >>> Kernelnewbies(a)kernelnewbies.org >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >>> >> You didn't finish your email such that ... . I would be glad to try and >> help if you finish off what your requirements are. >> Nick >> > > > Ooops, sorry, I didn't know that last fragment was there. I think the > previous part explains what I am looking for. > That's OK. You may want to look into virtual memory management of the kernel. However, I doubt that's what you want the issue is some that reallocates and takes advantage of CPU and already allowed kernel date structures. If that is the case look into writing a slab allocator for your security features you have added to the kernel. Further more writing a slab allocator is non trivial and you will need to look into the way memory is being handled in terms of hardware caches to find the best options with the slab functions in the kernel to get the best performable slab for your needs.This is link to a chapter in a book explaining this,https://www.kernel.org/doc/gorman/html/understand/understand011.htm. The only issue is the book is outdated in terms of kernel releases but the concepts are similar if not identical to the current releases. Hope this Helps, Nick

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Reusable Memory Manager
by Kenneth Adam Miller April 23, 2015

April 23, 2015

So, I have a particular use case that has a lot to do with security. Basically, we have a intended secure kernel version with grsecurity and other patches on it, and we have a specific application that has to do data filtering as an inline reference monitor. The problem is, there is throughput and design considerations that are limiting efficiency in the sense that it is highly difficult to make the system concurrent and also highly difficult to scale-all while also being secure. Basically, the memory regions have to be encoded at compile time because of the way kernel segregation works. This makes the security proof of the system far more simple and manageable; it's easy to say that no userland monitor which is being given access to a specific memory region can access outside of the region to which it is allocated, because it's statically set. The tradeoff here is pretty severe, because the static settings that have to be adopted pretty much mean that each particular monitor is given a specific memory region; if there's a lot of traffic to a specific monitor type, then that one type will be overwhelmed, but not even at the rate that the machine itself could support. This is because all the other cores are potentially sitting unused while the one in this worst case scenario is running out of memory and not able to dispatch work to more cores. So my ultimate question is: is there some reusable, dynamic memory allocation manager that can be used? I'm thinking that there has to, at the least, be the constructs by which user land processes are managed and divvied memory by the kernel itself. Does anybody know where that source would be? Where I can go in order to learn more about that? What we want is a secure way to dynamically allocate memory from these static memory page boundaries such that

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Question about porting over magic lantern kernel hardware support to mainline
by nick April 23, 2015

April 23, 2015

Greetings All, I was wondering about reading this forum page,http://www.magiclantern.fm/forum/index.php?topic=14847.0;prev_next=next#new if porting over magic lantern's change to the main line kernel is a good idea or does it need to be kept separate.Honestly, from my personal experience high resolution cameras running Linux may be of great use to thousands of independent film makers worldwide and it would be easier for vendors of said cameras to use the main line kernel for this and not a patched vendor kernel for supporting there hardware. If the camera vendors are very closed mine, then I would see no point in doing this. Anyhow please let me known of any options on main lining this or keeping it separate. Thanks, Nick

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Basic question about namespaces
by Bruno Ferreira April 22, 2015

April 22, 2015

Hi, I'm new in kernel programming.. I'm reading the chapter about namespaces in the "Linux Kernel Networking" (Rami Rosen), but I could not find a way to create a network namespace. I understand that I should use methods like create_nsproxy(), copy_net_ns() and create_new_namespaces(), but I don't know how to set their parameters. For example, the method copy_net_ns(unsigned long flags, struct user_namespace *user_ns, struct net *old_net), defined in net_namespace.h. I know that for flags, a may use CLONE_NEWNET, but what about the other parameters, user_ns and old_net? There is a good documentation (with examples) about this? Unfortunately the book wasn't detailed enough. I appreciate any help. -- Bruno A. C. Ferreira

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Question about shared interrupts in devicetree
by Stefan Wahren April 22, 2015

April 22, 2015

Hi, i'm currently working on drivers (regulator and power switch) for a power subsystem of a ARM9 processor (Freescale i.MX28). There are interrupts for the power subsystem which share the same interrupt line. This interrupt line is needed by both drivers (regulator and power switch). Now the question what is the right way (tm) to specify the interrupt in the devicetree and fetch the irq number during driver probe? Option A (define interrupt in parent node): power: power@80044000 { compatible = "fsl,imx28-power", "syscon"; reg = <0x80044000 0x2000>; interrupts = <6>; reg_vddd: regulator@1 { compatible = "fsl,imx28-vddd"; }; pswitch: pswitch@5 { compatible = "fsl,mxs-pswitch"; linux,code = <116>; }; } int irq = irq_of_parse_and_map(parent, 0); Option B (define interrupt for each child node): power: power@80044000 { compatible = "fsl,imx28-power", "syscon"; reg = <0x80044000 0x2000>; reg_vddd: regulator@1 { compatible = "fsl,imx28-vddd"; interrupts = <6>; }; pswitch: pswitch@5 { compatible = "fsl,mxs-pswitch"; linux,code = <116>; interrupts = <6>; }; } int irq = platform_get_irq(pdev, 0); Best regards Stefan

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kbuild- sub directroy makefile
by ratheesh kannoth April 22, 2015

April 22, 2015

******************Start of Makfile*********** ccflags += "-D DEXI" obj-m := hello.o ************End***************** Is there any way i can echo a string ...like "Hey i am building hello.o now " in this makefile ? I tries targets like genbin as per http://lxr.free-electrons.com/source/Documentation/kbuild/modules.txt?v=3.9. I dont think other targets would work as this is a sub-directory level makefile which is being called from top directroy. Any help is really appreciated Thanks, Ratheesh

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wait queues
by Ruben Safir April 22, 2015

April 22, 2015

I'm not pouring over Love's book in detail and the section in Chapter 4 on the wit queue is implemented in the text completely surprised me. He is recommending that you have to right your own wait queue entry routine for every process? Isn't that reckless? He is suggesting DEFINE_WAIT(wait) //what IS wait add_wait_queue(q, &wait); // in the current kernel this invovled // flag checking and a linked list while(!condition){ /* an event we are weighting for prepare_to_wait(&q, &wait, TASK_INTERRUPTIBLE); if(signal_pending(current)) /* SIGNAl HANDLE */ schedule(); } finish_wait(&q, &wait); He also write how this proceeds to function and one part confuses me 5. When the taks awakens, it again checks whether the condition is true. If it is, it exists the loop. Otherwise it again calls schedule. This is not the order that it seems to follow according to the code. To me it looks like it should 1 - creat2 the wait queue 2 - adds &wait onto queue q 3 checks if condition is true, if so, if not, enter a while loop 4 prepare_to_wait which changes the status of our &wait to TASK_INTERUPPABLE 5 check for signals ... notice the process is still moving. Does it stop and wait now? 6 schedule itself on the runtime rbtree... which make NO sense unless there was a stopage I didn't know about. 7 check the condition again and repeat while look 7a. if the loop ends fishish_waiting... take it off the queue. Isn't this reckless to leave this to users to write the code. Your begging for a race condition. Ruben _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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process tracking
by Mustafa Hussain April 21, 2015

April 21, 2015

I have reading recently how CFS works and I want to detect processes that is not used and have the policy SCHED_NORMAL, Can i do this by tracking load_weight for each process if the load dose not change over the time can i consider this process is not used ?

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Achieve multi-threading in MIPS assembly
by Chaturvedi, Akash April 21, 2015

April 21, 2015

Greetings All, I am writing MIPS assembly code for a 'Word guessing game'. I want to play a background music in the game at the time user plays. I am using MARS emulator for running and testing my code. As I need to do two task at the same time (game instructions and play music). Can someone please help me in achieving multi-threading using MIPS instructions (Like pthread_create in C). Or if there another way I can do two task simultaneously in MIPS assembly. Thanks, Akash UT Dallas

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