Messages in this thread | | | Subject | Re: what will connect the fork() with its following code ? a simple example below: | From | Bernd Petrovitsch <> | Date | Tue, 06 Sep 2005 12:37:55 +0200 |
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On Tue, 2005-09-06 at 17:15 +0800, Sat. wrote: > if(!(pid=fork())){ > ...... > printk("in child process"); > ...... > }else{ > ..... > printk("in father process"); > ..... > } > > this is a classical example, when the fork() system call runs, it will > build a new process and active it . while the schedule() select the > new process it will run. this is rather normal. > > but there is always a confusion in my minds. > because , sys_fork() only copies father process and configure some new > values., and do nothing . so the bridge between the new process and > its following code, printk("in child process"), seems disappear . so I
No, it is the same point as in the parent process - just the fork() call. In fact the fork() returns twice - once within the parent process (returning as result the pid of the child) and once within the child (returning 0) [ and we ignore the error case for simplicity ]. Basically you are not forced to do a if() or switch() on the return value(s) of fork() ---- snip ---- printf("1. fork() in process %d returned %d\n", getpid(), fork()); printf("2. fork() in process %d returned %d\n", getpid(), fork()); printf("3. fork() in process %d returned %d\n", getpid(), fork()); printf("4. fork() in process %d returned %d\n", getpid(), fork()); printf("5. fork() in process %d returned %d\n", getpid(), fork()); ---- snip ---- Put this in a main() function and try it out.
> always believe that the new process should have a pointer which point > the code "printk("in child process");". except this , there are not > any connection between them ?
The kernel doesn't know (or care) about the C code (e.g. if(), ...) in your application. The "pointer" (if you want to call it) is the normal instruction pointer (or what else it is called on your CPU).
> very confused :(
Bernd -- Firmix Software GmbH http://www.firmix.at/ mobil: +43 664 4416156 fax: +43 1 7890849-55 Embedded Linux Development and Services
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