Question

I am working on a project that modifies part of the Android OS, and when I tried to implement a new system call to return the status of all the processes, I encountered the following error:

kernel/sys.c: error: array tpye has incomplete element type. 

What I did in sys.c is the following:

/***previous code in sys.c***/

SYSCALL_DEFINE2(new_syscall, struct info __user*, buf, int __user*, nr){
    if(!buf || !nr) return -EINVAL;

    int nr_copy;
    int success;

    success = copy_from_user(&nr_copy, nr, sizeof(int));
    if(success == 0) return -EINVAL;
    if(nr_copy < 1) return -EINVAL;

    struct info buf_copy[nr_copy];  /*************

    return 0;
}

Complier complained about the line marked with stars.

My info.h file looks like this:

    #ifndef __LINUX_INFO_H
    #define __LINUX_INFO_H

    struct info {
        long state;         
        pid_t pid;          
        pid_t parent_pid;       
    };

    #endif

I tried including the info.h in sys.c, but it didn’t help at all. Can anyone provide me some directions on what I should look into?

Thanks

Answer 1

What compiler are you using? Dynamically sized arrays are a newish C feature that might not be supported. OTOH, they are allocated on the stack, and that is a very scarce commodity in-kernel. You should allocate memory for the array via kmalloc or one of its ilk.