Date: Mon, 14 Feb 2011 09:39:17 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: beezarliu <beezarliu@yahoo.com.cn> Subject: Re: map share memory to kernel space Message-ID: <201102140939.17486.jhb@freebsd.org> In-Reply-To: <201102141718415933573@yahoo.com.cn> References: <201102141718415933573@yahoo.com.cn>
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On Monday, February 14, 2011 4:18:50 am beezarliu wrote:
> Hackers,
>
> I want to access a userland share memory in a kernel thread.
> So I tried to map the share memory to the kernel space.
> The basic idea is to map the shm_object into kernel_map
> when the share memory is created.
>
> Using the following patch, I found the vm_object in kernel_map,
> and the vm_object in the address space of userland process are the same.
> But their content in the kernel and userland address mapped are different.
>
> It's very strang since they are exactly the same vm_object.
> Do I miss something, please help.
Hmm, this is a bit of code I use for something similar to map a VM object into
the kernel. It does not use vm_page_grab() directly though:
VM_OBJECT_LOCK(obj);
vm_object_reference_locked(obj);
VM_OBJECT_UNLOCK(obj);
/* Map the object into the kernel_map and wire it. */
kva = vm_map_min(kernel_map);
ofs = foff & PAGE_MASK;
foff = trunc_page(foff);
size = round_page(size + ofs);
rv = vm_map_find(kernel_map, obj, foff, &kva, size, TRUE,
VM_PROT_READ | VM_PROT_WRITE, VM_PROT_READ | VM_PROT_WRITE, 0);
if (rv == KERN_SUCCESS) {
rv = vm_map_wire(kernel_map, kva, kva + size,
VM_MAP_WIRE_SYSTEM | VM_MAP_WIRE_NOHOLES);
if (rv == KERN_SUCCESS) {
*memp = (void *)(kva + ofs);
return (0);
}
vm_map_remove(kernel_map, kva, kva + size);
} else
vm_object_deallocate(obj);
Unmapping the object is easy of course:
kva = (vm_offset_t)mem;
ofs = kva & PAGE_MASK;
kva = trunc_page(kva);
size = round_page(size + ofs);
vm_map_remove(kernel_map, kva, kva + size);
--
John Baldwin
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