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  • Interpreting segfault messages

    - by knorv
    What is the correct interpretation of the following segfault messages? segfault at 10 ip 00007f9bebcca90d sp 00007fffb62705f0 error 4 in libQtWebKit.so.4.5.2[7f9beb83a000+f6f000] segfault at 10 ip 00007fa44d78890d sp 00007fff43f6b720 error 4 in libQtWebKit.so.4.5.2[7fa44d2f8000+f6f000] segfault at 11 ip 00007f2b0022acee sp 00007fff368ea610 error 4 in libQtWebKit.so.4.5.2[7f2aff9f7000+f6f000] segfault at 11 ip 00007f24b21adcee sp 00007fff7379ded0 error 4 in libQtWebKit.so.4.5.2[7f24b197a000+f6f000]

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  • linux firewall in c

    - by asha
    i m implementing a firewall for linux,i want to block packets using loadable kernal module(lkm). please help me how can i do it ? i just know that it can be done by lkm by using some function in it,like init(),clean_up. i want to know how to use DROP,ACCEPT in blocking function within lkm. i want to do it without iptable command.

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  • Linux memory fragmentation

    - by Raghu
    Hi all, Is there a way to detect memory fragmentation on linux ? This is because on some long running servers I have noticed performance degradation and only after I restart process I see better performance. I noticed it more when using linux huge page support -- are huge pages in linux more prone to fragmentation ? I have looked at /proc/buddyinfo in particular. I want to know whether there are any better ways to look at it.

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  • How to define GPS module in Android?

    - by Osama Gamal
    I'm porting android to Devkit8000 which is a BeagleBoard clone. I have a GPS module connected on /dev/ttyS0. I could successfully get NMEA output when writing "cat /dev/ttyS0" in the terminal emulator. I want to know how to let android know that there is a GPS module on /dev/ttyS0 and it is outputting NMEA standard? To be able to use the android.location class with it! Is there something to edit in the android's source? adding driver for example, writing a code with android-ndk or what?

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  • Memory assignment of local variables

    - by Mask
    void function(int a, int b, int c) { char buffer1[5]; char buffer2[10]; } We must remember that memory can only be addressed in multiples of the word size. A word in our case is 4 bytes, or 32 bits. So our 5 byte buffer is really going to take 8 bytes (2 words) of memory, and our 10 byte buffer is going to take 12 bytes (3 words) of memory. That is why SP is being subtracted by 20. Why it's not ceil((5+10)/4)*4=16?

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  • Why doesn't Linux use the hardware context switch via the TSS?

    - by smwikipedia
    Hi guys! I read the following statement: The x86 architecture includes a specific segment type called the Task State Segment (TSS), to store hardware contexts. Although Linux doesn't use hardware context switches, it is nonetheless forced to set up a TSS for each distinct CPU in the system. I am wondering: Why doesn't Linux use the hardware support for context switch? Isn't the hardware approach much faster than the software approach? Is there any OS which does take advantage of the hardware context switch? Does windows use it? At last and as usual, thanks for your patience and reply.

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  • Sources of latency in sending-receiving tcp/udp packets in linux

    - by osgx
    Hello What are sources of latency in process of sending/receiving tcp/udp packets in linux 2.6 ? I want to know a latency sources in "ping-pong" latency tests. There are some rather good papers of ethernet latency, but they cover only latency sources in the wire and switch (and rather cursory, only for specific switch). What steps of processing does follow a packet? Papers with deep latency analysis of usual ping (icmp) will be useful too. I rely on community :)

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  • Is writing to a socket an arbitrary limitation of the sendfile() syscall?

    - by Sufian
    Prelude sendfile() is an extremely useful syscall for two reasons: First, it's less code than a read()/write() (or recv()/send() if you prefer that jive) loop. Second, it's faster (less syscalls, implementation may copy between devices without buffer, etc...) than the aforementioned methods. Less code. More efficient. Awesome. In UNIX, everything is (mostly) a file. This is the ugly territory from the collision of platonic theory and real-world practice. I understand that sockets are fundamentally different than files residing on some device. I haven't dug through the sources of Linux/*BSD/Darwin/whatever OS implements sendfile() to know why this specific syscall is restricted to writing to sockets (specifically, streaming sockets). I just want to know... Question What is limiting sendfile() from allowing the destination file descriptor to be something besides a socket (like a disk file, or a pipe)?

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  • Does copy_from_user modify the user pointer?

    - by Michael
    Does the copy_from_user function, declared in uaccess.h, modify the (void __user *)from pointer? The pointer isn't declared as const in the function declaration, only the contents it points to. The reason I ask is that I want to use copy_from_user twice, with the second copy_from_user copying from the place where the first one finished. I was planning on doing something like this, is it guaranteed to work? //buf is a user pointer that is already defined copy_from_user(my_first_alloced_region, buf, some_size); //do stuff copy_from_user(my_second_alloced_region, buf + some_size, some_other_size); Thanks in advance.

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  • About fork system call and global variables

    - by lurks
    I have this program in C++ that forks two new processes: #include <pthread.h> #include <iostream> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h> #include <cstdlib> using namespace std; int shared; void func(){ extern int shared; for (int i=0; i<10;i++) shared++; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } int main(){ extern int shared; pid_t p1,p2; int status; shared=0; if ((p1=fork())==0) {func();exit(0);}; if ((p2=fork())==0) {func();exit(0);}; for(int i=0;i<10;i++) shared++; waitpid(p1,&status,0); waitpid(p2,&status,0);; cout<<"shared variable is: "<<shared<<endl; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } The two forked processes make an increment on the shared variables and the parent process does the same. As the variable belongs to the data segment of each process, the final value is 10 because the increment is independent. However, the memory address of the shared variables is the same, you can try compiling and watching the output of the program. How can that be explained ? I cannot understand that, I thought I knew how the fork() works, but this seems very odd.. I need an explanation on why the address is the same, although they are separate variables.

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  • A question for retrieve minix os version

    - by majnun
    Hi guys i'm having a project for the university in which (above others ) i have to get the minix os version from kernell call.I'm not a very experienced programmer so this is what i have come to (with some help ) int main (int argc, char *argv[] ) { char M3ca1[23]; message ml; m.m_u.m_m1.m3ca1= OS_VERSION; char temp=_syscall(MM,69,&m); printf("the os version is %c\n",temp); return 0; } and i get multiple errors.IF you have any ideas it would be greatly appreciated.

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  • Maximum number of files one ext3 directory while still getting acceptable performance?

    - by knorv
    I have an application writing to an ext3 directory which over time has grown to roughly three million files. Needless to say, reading the file listing of this directory is unbearably slow. I don't blame ext3. The proper solution would have been to let the directory write to sub-directories such as ./a/b/c/abc.ext rather than just ./abc.ext. I'm changing to such a sub-directory structure and my question is simply: roughly how many files should I expect to store in one ext3 directory while still getting acceptable performance? Or in other words; assuming that I need to store three million files in the structure, how many levels deep should the ./a/b/c/abc.ext structure be? Obviously this is a question that cannot be answered exactly, but I'm looking for a ball park estimate.

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  • "STI", in the protected mode,CPU will restart.

    - by user299668
    INTEL X86 Platform. My programme run start at 2M absolute address in protected mode,everything seems ok, but when i enable interrupt with "sti", the CPU will restart. Why? is there any necessary initialization before "enbale interrupt"? i have setup the idtptr, but it seems no work.

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  • Linux Scheduling Mechanism in 2.6.22?

    - by Mazen
    Hello, I'm doing some kind of performance evaluation using two different vanilla Linux kernels, 2.6.22 and 2.6.31, since I assume each of them uses a different scheduling mechanism: 2.6.22 uses the old O(1) scheduler, whilst 2.6.31 adopts the CFS. Could anybody confirm the correction of this assumption?

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  • Operating system scheduler question

    - by ual
    I recently asked myself: If a program, like Mozilla Firefox for example, is started - the control must be somehow given to it. But when the program crashes, why doesn't my whole system crash like in early Windows version? How can Windows take back the control from the program, or even not give it to it fully? (Note: This is not my homework; I go to school but in my informatics class are really only guys that would answer with "Can I eat that?" when I ask them about kernels. Same with my teacher.)

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  • Operating system question

    - by ual
    I recently asked myself: If a program, like Mozilla Firefox for example, is started - the control must be somehow given to it. But when the program crashes, why doesn't my whole system crash like in early Windows version? How can Windows take back the control from the program, or even not give it to it fully? (Note: This is not my homework; I go to school but in my informatics class are really only guys that would answer with "Can I eat that?" when I ask them about kernels. Same with my teacher.)

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  • where did the _syscallN macros go in <linux/unistd.h>?

    - by Evan Teran
    It used to be the case that if you needed to make a system call directly in linux without the use of an existing library, you could just include <linux/unistd.h> and it would define a macro similar to this: #define _syscall3(type,name,type1,arg1,type2,arg2,type3,arg3) \ type name(type1 arg1,type2 arg2,type3 arg3) \ { \ long __res; \ __asm__ volatile ("int $0x80" \ : "=a" (__res) \ : "0" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2)), \ "d" ((long)(arg3))); \ if (__res>=0) \ return (type) __res; \ errno=-__res; \ return -1; \ } Then you could just put somewhere in your code: _syscall3(ssize_t, write, int, fd, const void *, buf, size_t, count); which would define a write function for you that properly performed the system call. It seems that this system has been superseded by something (i am guessing that "[vsyscall]" page that every process gets) more robust. So what is the proper way (please be specific) for a program to perform a system call directly on newer linux kernels? I realize that I should be using libc and let it do the work for me. But let's assume that I have a decent reason for wanting to know how to do this :-).

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