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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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  • data path (travel) of tcp data from "write" syscall downto I/O registers programming

    - by osgx
    Hello Is there a good overview of tcp data path in Linux (2.6, not 2.4 if the path actually differ)? Where is a packet on different stages of tcp/ip stack handling? How packet is packed to tcp segment, then ip packet. How it is transmitted to network card? (with series of I/O regs write and DMA?) Is it transmitted to network card in the "write" syscall handler (with some deep callstack) or is it transmitted at some other moment?

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  • Storage drives is causting system crash

    - by Chad
    I'm running Centos 5.4 with 750GB(ntfs) and 2TB drives for storage. Originally I installed the 750, everything seemed fine and then I installed the 2TB drive with NTFS already partitioned. I noticed when I would copy a lot of videos it would crash (no mouse or response from server) about 20min into it. After doing some troubleshooting I noticed the 750 would also crash when doing the same task so I decided that NTFS may be the problem. I unmounted the 2TB drive and tried to partition and format it using ext2 but when using parted it would crash at this point "writing inode tables". Looking at the dmesg logs I believe this is the error "mtrr: type mismatch for e0000000,10000000 old: write-back new: write-combining". Any idea as to what could be causing this?

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  • how to add language support to android

    - by avar
    hello i hope someone put me on the right direction with my problem i want to work on supporting my language, specially the writing on android we use Arabic characters with little modification ( like parsi, urdu etc).. i was hoping android has fully supported Arabic , then i would make changes to work with my language. but even 2.2 dosn't support Arabic . it just show Arabic characters and it is not connected. that is "????? " is displayed "? ? ? ? ?". some individuals have made Arabic support on CyanogenMod ROM's for some HTC phones, but they would not tell how they made it. I'v got the android source code, i want to know where to start, where to make changes , what is the library that handle fonts , shaping engine etc .. ps : android.com and other android related google groups are blocked in my country.

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  • Virtual audio driver (microphone)

    - by Dalamber
    Hello guys, I want to develop a virtual microphone driver. Please, do not say anything about DirectShow - that's not "the way". I need a solution that will work with any software including Skype and MSN. And DirectShow doesn't fit these requirements. I found AVStream Filter-Centric Simulated Capture Driver (avssamp.sys) in Windows 7 WDK. What I need is an audio part of it. By default it reads avssamp.wav and plays it. But this driver is registered as WDM streaming capture device. And I want it in Audio Capture Device. There are some posts in the web but they are all the same: http://www.tech-archive.net/Archive/Development/microsoft.public.development.device.drivers/2005-05/msg00124.html http://www.winvistatips.com/problem-installing-avssamp-audio-capture-sources-category-t184898.html I think registering this filter-driver as audio capture device will make Skype recognize it as a microphone and thefore I will be able to push any PCM file as if it goes from mic. If someone already faced this problem before, please help. Thanks in advance.

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  • Maximum number of files in 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 application code write to sub-directories such as ./a/b/c/abc.ext rather than using only ./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? What's your experience? 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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  • spin_lock_irqsave vs spin_lock_irq

    - by cojocar
    On a SMP machine we must use spin_lock_irqsave and not spin_lock_irq from interrupt context. Why would we want to save the flags (which contains the IF)? Is there another interrupt routine that could interrupt us? The flags are per CPU?

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  • How to R/W hard disk when CPU is in Protect Mode?

    - by smwikipedia
    I am doing some OS experiment. Until now, all my code utilized the real mode BIOS interrupt to manipulate hard disk and floppy. But once my code enabled the Protect Mode of the CPU, all the real mode BIOS interrupt service routine won't be available. How could I R/W the hard disk and floppy? I have a feeling that I need to do some hardware drivers now. Am I right? Is this why an OS is so difficult to develop? I know that hardwares are all controlled by reading from and writing to certain control or data registers. For example, I know that the Command Block Registers of hard disk range from 0x1F0 to 0x1F7. But I am wondering whether the register addresses of so many different hardwares are the same on the PC platform? Or do I have to detect that before using them? How to detect them?? For any responses I present my deep appreciation.

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  • Implementing a kext that intercepts file system usage.

    - by UraN
    Hi, how do most of antivirus software block file system io in case of an infected file? I suppose all the magic resides in some custom kext to do that. Can anyone point me to some topics on this? Some working example would also be great. I've read apple docs about kext development, but mostly it's all about hardware drivers and i could not find what i need. Thanx.

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