On Fri, Jun 28, 2024 at 2:33 AM Mina Almasry <almasrymina@xxxxxxxxxx> wrote: > > In tcp_recvmsg_locked(), detect if the skb being received by the user > is a devmem skb. In this case - if the user provided the MSG_SOCK_DEVMEM > flag - pass it to tcp_recvmsg_devmem() for custom handling. > > tcp_recvmsg_devmem() copies any data in the skb header to the linear > buffer, and returns a cmsg to the user indicating the number of bytes > returned in the linear buffer. > > tcp_recvmsg_devmem() then loops over the unaccessible devmem skb frags, > and returns to the user a cmsg_devmem indicating the location of the > data in the dmabuf device memory. cmsg_devmem contains this information: > > 1. the offset into the dmabuf where the payload starts. 'frag_offset'. > 2. the size of the frag. 'frag_size'. > 3. an opaque token 'frag_token' to return to the kernel when the buffer > is to be released. > > The pages awaiting freeing are stored in the newly added > sk->sk_user_frags, and each page passed to userspace is get_page()'d. > This reference is dropped once the userspace indicates that it is > done reading this page. All pages are released when the socket is > destroyed. > > Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx> > Signed-off-by: Kaiyuan Zhang <kaiyuanz@xxxxxxxxxx> > Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx> Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
