p_vmspace in syscall

[Nicolas Cormier]

On 7/4/07, Robert Watson <rwatson at freebsd.org> wrote:
>
> On Mon, 2 Jul 2007, Nicolas Cormier wrote:
>
> > I am trying to map some data allocated in kernel to a user process (via a
> > syscall). I need the proc's vmspace, but the value of p_vmspace of the input
> > proc argument is NULL ... How can I get a valid vmspace ?
>
> When operating in a system call, the 'td' argument to the system call function
> is the current thread pointer.  You can follow td->td_proc to get to the
> current process (and therefore, its address space).  In general, I prefer
> mapping user pages into kernel instead of kernel pages into user space, as it
> reduces the chances of leakage of kernel data to user space, and there are
> some useful primitives for making this easier.  For example, take a look at
> the sf_buf infrastructure used for things like socket zero-copy send, which
> manages a temporary kernel mapping for a page.
>

Yes Roman told me in private that I'm wrong with the first argument, I
thought that it was a proc*...

For my module I try to create a simple interface of a network allocator:
User code should look like this:

unsigned id;
void* data = netmalloc(host, size, &id);
memcpy(data, "toto", sizeof("toto");
netdetach(data);

and later in another process:
void* data = netattach(host, id);
...
netfree(data);

netmalloc syscall does something like that:
- query distant host to allocate size
- receive an id from distant host
- malloc in kernel size
- map the buffer to user process (*)

netdetach syscall:
- send data to distant host

netattach syscall:
- get data from host
- malloc in kernel size
- map the buffer to user process (*)

* I already watch the function vm_pgmoveco
(http://fxr.watson.org/fxr/source/kern/kern_subr.c?v=RELENG62#L78)

I used pgmoveco as follow:

vm_map_t mapa = &proc->p_vmspace->vm_map,
size = round_page(size);
void* data = malloc(size,  M_NETMALLOC, M_WAITOK);
vm_offset_t addr = vm_map_min(mapa);
vm_map_find(mapa, NULL, 0, &addr, size, TRUE, VM_PROT_ALL,
VM_PROT_ALL, MAP_NOFAULT);
vm_pgmoveco(mapa, (vm_offset_t)data, addr);


With this I have a panic with vm_page_insert, I am not sure to
understand the reason of this panic. I can't have multiple virtual
pages on the same physical page ?

Thanks!
-- 
Nicolas Cormier