Re: [PATCH RFC net-next v4 3/8] vsock: support multi-transport datagrams
From: Stefano Garzarella
Date: Mon Jun 26 2023 - 10:51:30 EST
On Fri, Jun 23, 2023 at 02:59:23AM +0000, Bobby Eshleman wrote:
On Fri, Jun 23, 2023 at 02:50:01AM +0000, Bobby Eshleman wrote:
On Thu, Jun 22, 2023 at 05:19:08PM +0200, Stefano Garzarella wrote:
> On Sat, Jun 10, 2023 at 12:58:30AM +0000, Bobby Eshleman wrote:
> > This patch adds support for multi-transport datagrams.
> >
> > This includes:
> > - Per-packet lookup of transports when using sendto(sockaddr_vm)
> > - Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
> > sockaddr_vm
> >
> > To preserve backwards compatibility with VMCI, some important changes
> > were made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
> > be used for dgrams iff there is not yet a g2h or h2g transport that has
>
> s/iff/if
>
> > been registered that can transmit the packet. If there is a g2h/h2g
> > transport for that remote address, then that transport will be used and
> > not "transport_dgram". This essentially makes "transport_dgram" a
> > fallback transport for when h2g/g2h has not yet gone online, which
> > appears to be the exact use case for VMCI.
> >
> > This design makes sense, because there is no reason that the
> > transport_{g2h,h2g} cannot also service datagrams, which makes the role
> > of transport_dgram difficult to understand outside of the VMCI context.
> >
> > The logic around "transport_dgram" had to be retained to prevent
> > breaking VMCI:
> >
> > 1) VMCI datagrams appear to function outside of the h2g/g2h
> > paradigm. When the vmci transport becomes online, it registers itself
> > with the DGRAM feature, but not H2G/G2H. Only later when the
> > transport has more information about its environment does it register
> > H2G or G2H. In the case that a datagram socket becomes active
> > after DGRAM registration but before G2H/H2G registration, the
> > "transport_dgram" transport needs to be used.
>
> IIRC we did this, because at that time only VMCI supported DGRAM. Now that
> there are more transports, maybe DGRAM can follow the h2g/g2h paradigm.
>
Totally makes sense. I'll add the detail above that the prior design was
a result of chronology.
> >
> > 2) VMCI seems to require special message be sent by the transport when a
> > datagram socket calls bind(). Under the h2g/g2h model, the transport
> > is selected using the remote_addr which is set by connect(). At
> > bind time there is no remote_addr because often no connect() has been
> > called yet: the transport is null. Therefore, with a null transport
> > there doesn't seem to be any good way for a datagram socket a tell the
> > VMCI transport that it has just had bind() called upon it.
>
> @Vishnu, @Bryan do you think we can avoid this in some way?
>
> >
> > Only transports with a special datagram fallback use-case such as VMCI
> > need to register VSOCK_TRANSPORT_F_DGRAM.
>
> Maybe we should rename it in VSOCK_TRANSPORT_F_DGRAM_FALLBACK or
> something like that.
>
> In any case, we definitely need to update the comment in
> include/net/af_vsock.h on top of VSOCK_TRANSPORT_F_DGRAM mentioning
> this.
>
Agreed. I'll rename to VSOCK_TRANSPORT_F_DGRAM_FALLBACK, unless we find
there is a better way altogether.
> >
> > Signed-off-by: Bobby Eshleman <bobby.eshleman@xxxxxxxxxxxxx>
> > ---
> > drivers/vhost/vsock.c | 1 -
> > include/linux/virtio_vsock.h | 2 -
> > net/vmw_vsock/af_vsock.c | 78 +++++++++++++++++++++++++--------
> > net/vmw_vsock/hyperv_transport.c | 6 ---
> > net/vmw_vsock/virtio_transport.c | 1 -
> > net/vmw_vsock/virtio_transport_common.c | 7 ---
> > net/vmw_vsock/vsock_loopback.c | 1 -
> > 7 files changed, 60 insertions(+), 36 deletions(-)
> >
> > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > index c8201c070b4b..8f0082da5e70 100644
> > --- a/drivers/vhost/vsock.c
> > +++ b/drivers/vhost/vsock.c
> > @@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
> > .cancel_pkt = vhost_transport_cancel_pkt,
> >
> > .dgram_enqueue = virtio_transport_dgram_enqueue,
> > - .dgram_bind = virtio_transport_dgram_bind,
> > .dgram_allow = virtio_transport_dgram_allow,
> > .dgram_get_cid = virtio_transport_dgram_get_cid,
> > .dgram_get_port = virtio_transport_dgram_get_port,
> > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> > index 23521a318cf0..73afa09f4585 100644
> > --- a/include/linux/virtio_vsock.h
> > +++ b/include/linux/virtio_vsock.h
> > @@ -216,8 +216,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
> > u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
> > bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
> > bool virtio_transport_stream_allow(u32 cid, u32 port);
> > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> > - struct sockaddr_vm *addr);
> > bool virtio_transport_dgram_allow(u32 cid, u32 port);
> > int virtio_transport_dgram_get_cid(struct sk_buff *skb, unsigned int *cid);
> > int virtio_transport_dgram_get_port(struct sk_buff *skb, unsigned int *port);
> > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > index 74358f0b47fa..ef86765f3765 100644
> > --- a/net/vmw_vsock/af_vsock.c
> > +++ b/net/vmw_vsock/af_vsock.c
> > @@ -438,6 +438,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
> > return transport;
> > }
> >
> > +static const struct vsock_transport *
> > +vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
> > +{
> > + const struct vsock_transport *transport;
> > +
> > + transport = vsock_connectible_lookup_transport(cid, flags);
> > + if (transport)
> > + return transport;
> > +
> > + return transport_dgram;
> > +}
> > +
> > /* Assign a transport to a socket and call the .init transport callback.
> > *
> > * Note: for connection oriented socket this must be called when vsk->remote_addr
> > @@ -474,7 +486,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
> >
> > switch (sk->sk_type) {
> > case SOCK_DGRAM:
> > - new_transport = transport_dgram;
> > + new_transport = vsock_dgram_lookup_transport(remote_cid,
> > + remote_flags);
> > break;
> > case SOCK_STREAM:
> > case SOCK_SEQPACKET:
> > @@ -691,6 +704,9 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
> > static int __vsock_bind_dgram(struct vsock_sock *vsk,
> > struct sockaddr_vm *addr)
> > {
> > + if (!vsk->transport || !vsk->transport->dgram_bind)
> > + return -EINVAL;
> > +
> > return vsk->transport->dgram_bind(vsk, addr);
> > }
> >
> > @@ -1172,19 +1188,24 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> >
> > lock_sock(sk);
> >
> > - transport = vsk->transport;
> > -
> > - err = vsock_auto_bind(vsk);
> > - if (err)
> > - goto out;
> > -
> > -
> > /* If the provided message contains an address, use that. Otherwise
> > * fall back on the socket's remote handle (if it has been connected).
> > */
> > if (msg->msg_name &&
> > vsock_addr_cast(msg->msg_name, msg->msg_namelen,
> > &remote_addr) == 0) {
> > + transport = vsock_dgram_lookup_transport(remote_addr->svm_cid,
> > + remote_addr->svm_flags);
> > + if (!transport) {
> > + err = -EINVAL;
> > + goto out;
> > + }
> > +
> > + if (!try_module_get(transport->module)) {
> > + err = -ENODEV;
> > + goto out;
> > + }
> > +
> > /* Ensure this address is of the right type and is a valid
> > * destination.
> > */
> > @@ -1193,11 +1214,27 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> > remote_addr->svm_cid = transport->get_local_cid();
> >
>
> From here ...
>
> > if (!vsock_addr_bound(remote_addr)) {
> > + module_put(transport->module);
> > + err = -EINVAL;
> > + goto out;
> > + }
> > +
> > + if (!transport->dgram_allow(remote_addr->svm_cid,
> > + remote_addr->svm_port)) {
> > + module_put(transport->module);
> > err = -EINVAL;
> > goto out;
> > }
> > +
> > + err = transport->dgram_enqueue(vsk, remote_addr, msg, len);
>
> ... to here, looks like duplicate code, can we get it out of the if block?
>
Yes, I think using something like this:
[...]
bool module_got = false;
[...]
if (!try_module_get(transport->module)) {
err = -ENODEV;
goto out;
}
module_got = true;
[...]
out:
if (likely(transport && !err && module_got))
Actually, just...
if (module_got)
Yep, I think it should work ;-)
Thanks,
Stefano