This function is a Luna alternative to fork() and exec().
Why? Simply because I can't figure out for the life of me how to implement a working fork().
So meanwhile, we have spawn() as a replacement. exec() still exists, though.
This new device uses the seeded Mersenne PRNG we use in the kernel.
This device is not meant for regular userspace use, but more for userspace to seed their own PRNGs from.
If the DeviceFS is mounted at /dev, this device can be found at /dev/random.
The only thing doing weird stuff is exec(), so that's commented out and throws ENOSYS right now.
But we have two user tasks running in parallel, isolated from each other!
We have now proven that exec() does fail and return to userspace when a file is not a valid executable.
We can now go back to executing a normal program.
read() and close() are in unistd.h, but open() in fnctl.h.
I thought only the definitions for O_SOMETHING were in fnctl.h, but it is as it is.
Don't know why, but let's not anger the Unix gods.
The FILE* C API is pending as well.
Kernel: Implement a descriptor struct which stores the opened node and read offset, and give each task 8 of those.
Implement three syscalls: sys_read, sys_open and sys_close (sys_write still writes to the console instead of using a fd, for now)
Implement three new errors: ENOENT, EBADF and EMFILE.
libc: Implement the new errors, and the new syscalls in syscall().
Also fix _RETURN_WITH_ERRNO() to set errno correctly, which was making strerror() return null, thus crashing perror().
userspace: make init demonstrate the new file API.
%m as a format specifier is a nonstandard glibc extension, but I like it so I'm implementing it.
What it does is print the value of strerror(errno), without consuming any arguments to printf().
The exit() libc function already accepted an integer, but didn't pass it on to the kernel since we had no mechanism for it to do that.
Now, the kernel stores a task's exit status to display it later (and in the future, return it to userspace via wait()/waitpid())
