Re: allocate memory in userspace (Answer)

[Timo Benk]

Hi,

I found the following function in arch/i386/kernel/sys_i386.c:

---<snip>---
/* common code for old and new mmaps */
long do_mmap2
	(
		unsigned long addr, unsigned long len,
		unsigned long prot, unsigned long flags,
		unsigned long fd,   unsigned long pgoff
	)
{
	int error = -EBADF;
	struct file * file = NULL;

	flags &= ~(MAP_EXECUTABLE | MAP_DENYWRITE);
	if (!(flags & MAP_ANONYMOUS)) {
		file = fget(fd);
		if (!file)
			goto out;
	}

	down_write(&current->mm->mmap_sem);
	error = do_mmap_pgoff(file, addr, len, prot, flags, pgoff);
	up_write(&current->mm->mmap_sem);

	if (file)
		fput(file);
out:
	return error;
}
---<snap>---

the following code works for me(of course
don't forget to munmap the memory).
---<snip>---	
	char *userspace;
	char kernelspace[2048];

	userspace = (char*)do_mmap2
			(
				0, 
				2048, 
				PROT_READ|PROT_WRITE, 
				MAP_PRIVATE|MAP_ANON, 
				-1, 
				0
			);
			
	copy_to_user( userspace, "/dev/hda", 9 );
	
	copy_from_user( kernelspace, userspace, 9 );
	printk("%s\n",kernelspace);
---<snap>---	

Hope that helps any other struggling newbie:-)

-timo

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