Hi Dave, Thanks for reply. My English is not very good, and so I want to ask about a term:map. Does map mean that create a relationship between the virtual space and physical memory? Thanks again! 在 2012年4月18日 下午4:17，Dave Hylands <dhylands@gmail.com>写道：
Hi ,
On Wed, Apr 18, 2012 at 12:44 AM, 夏业添 <summerxyt@gmail.com> wrote:
Hi everyone,
there are some functions can alloc memory in kernel, but it seems that I cannot use it directly. Here is my code:
static int mytest_vm(){
struct vm_struct *v_start;
v_start=alloc_vm_area(PAGE_SIZE,NULL); //the kernel api has changed, I don't understand why there is a second parameter if(v_start==NULL){ printk("cannot alloc page\n"); return -1; }
sprintf((char *)v_start->addr,"this is a test.\n"); printk("after sprintk:%s",(char *)v_start->addr);
free_vm_area(v_start);
return 0; } module_init(mytest_vm);
but it just got a kernel Oops. Can anyone explain this to me? Thanks very much!
If my understanding of things is correct, this just allocates virtual space. That virtual space isn't backed by any physical pages.
The normal kernel allocators are things like kmalloc and vmalloc.
-- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com