Date: Wed, 4 Jul 2007 11:00:54 +0200 From: "Nicolas Cormier" <n.cormier@gmail.com> To: "Robert Watson" <rwatson@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: p_vmspace in syscall Message-ID: <c4630b800707040200n4a6de4f5j2008f60fefb149e6@mail.gmail.com> In-Reply-To: <20070704091349.T42421@fledge.watson.org> References: <c4630b800707020954s4aa0be68t2d5f3eb864f2dda5@mail.gmail.com> <20070704091349.T42421@fledge.watson.org>
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On 7/4/07, Robert Watson <rwatson@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
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