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 _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"