On 10/9/24 21:44, Mina Almasry wrote:
On Mon, Oct 7, 2024 at 3:16 PM David Wei <dw@xxxxxxxxxxx> wrote:
From: Pavel Begunkov <asml.silence@xxxxxxxxx>
Currently net_iov stores a pointer to struct dmabuf_genpool_chunk_owner,
which serves as a useful abstraction to share data and provide a
context. However, it's too devmem specific, and we want to reuse it for
other memory providers, and for that we need to decouple net_iov from
devmem. Make net_iov to point to a new base structure called
net_iov_area, which dmabuf_genpool_chunk_owner extends.
Similar feeling to Stan initially. I also thought you'd reuse
dmabuf_genpool_chunk_owner. Seems like you're doing that but also
renaming it to net_iov_area almost, which seems fine.
I guess, with this patch, there is no way to tell, given just a
net_iov whether it's dmabuf or something else, right? I wonder if
By intention there is no good/clear way to tell if it's a dmabuf
or page backed net_iov in the generic path, but you can easily
check if it's devmem or io_uring by comparing page pool's ops.
net_iov::pp should always be available when it's in the net stack.
5/15 does exactly that in the devmem tcp portion of tcp.c.
that's an issue. In my mind when an skb is in tcp_recvmsg() we need to
make sure it's a dmabuf net_iov specifically to call
tcp_recvmsg_dmabuf for example. I'll look deeper here.
Mentioned above, patch 5/15 handles that.
static inline struct dmabuf_genpool_chunk_owner *
-net_iov_owner(const struct net_iov *niov)
+net_devmem_iov_to_chunk_owner(const struct net_iov *niov)
{
- return niov->owner;
-}
+ struct net_iov_area *owner = net_iov_owner(niov);
-static inline unsigned int net_iov_idx(const struct net_iov *niov)
-{
- return niov - net_iov_owner(niov)->niovs;
+ return container_of(owner, struct dmabuf_genpool_chunk_owner, area);
Couldn't this end up returning garbage if the net_iov is not actually
a dmabuf one? Is that handled somewhere in a later patch that I
missed?
Surely it will if someone manages to use it with non-devmem net_iovs,
which is why I renamed it to "devmem*".
--
Pavel Begunkov
