Re: [RFC PATCH v5 11/19] virtio/vsock: dequeue callback for SOCK_SEQPACKET
From: Michael S. Tsirkin
Date: Wed Feb 24 2021 - 01:44:15 EST
On Wed, Feb 24, 2021 at 08:07:48AM +0300, Arseny Krasnov wrote:
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On 23.02.2021 17:17, Michael S. Tsirkin wrote:
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> On Thu, Feb 18, 2021 at 08:39:37AM +0300, Arseny Krasnov wrote:
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>> This adds transport callback and it's logic for SEQPACKET dequeue.
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>> Callback fetches RW packets from rx queue of socket until whole record
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>> is copied(if user's buffer is full, user is not woken up). This is done
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>> to not stall sender, because if we wake up user and it leaves syscall,
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>> nobody will send credit update for rest of record, and sender will wait
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>> for next enter of read syscall at receiver's side. So if user buffer is
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>> full, we just send credit update and drop data. If during copy SEQ_BEGIN
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>> was found(and not all data was copied), copying is restarted by reset
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>> user's iov iterator(previous unfinished data is dropped).
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>>
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>> Signed-off-by: Arseny Krasnov <arseny.krasnov@xxxxxxxxxxxxx>
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>> ---
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>> include/linux/virtio_vsock.h | 10 +++
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>> include/uapi/linux/virtio_vsock.h | 16 ++++
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>> net/vmw_vsock/virtio_transport_common.c | 114 ++++++++++++++++++++++++
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>> 3 files changed, 140 insertions(+)
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>>
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>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
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>> index dc636b727179..003d06ae4a85 100644
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>> --- a/include/linux/virtio_vsock.h
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>> +++ b/include/linux/virtio_vsock.h
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>> @@ -36,6 +36,11 @@ struct virtio_vsock_sock {
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>> u32 rx_bytes;
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>> u32 buf_alloc;
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>> struct list_head rx_queue;
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>> +
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>> + /* For SOCK_SEQPACKET */
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>> + u32 user_read_seq_len;
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>> + u32 user_read_copied;
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>> + u32 curr_rx_msg_cnt;
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>
>
> wrap these in a struct to make it's clearer they
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> are related?
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Ack
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>
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>> };
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>>
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>> struct virtio_vsock_pkt {
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>> @@ -80,6 +85,11 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
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>> struct msghdr *msg,
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>> size_t len, int flags);
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>>
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>> +int
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>> +virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
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>> + struct msghdr *msg,
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>> + int flags,
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>> + bool *msg_ready);
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>> s64 virtio_transport_stream_has_data(struct vsock_sock *vsk);
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>> s64 virtio_transport_stream_has_space(struct vsock_sock *vsk);
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>>
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>> diff --git a/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
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>> index 1d57ed3d84d2..cf9c165e5cca 100644
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>> --- a/include/uapi/linux/virtio_vsock.h
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>> +++ b/include/uapi/linux/virtio_vsock.h
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>> @@ -63,8 +63,14 @@ struct virtio_vsock_hdr {
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>> __le32 fwd_cnt;
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>> } __attribute__((packed));
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>>
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>> +struct virtio_vsock_seq_hdr {
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>> + __le32 msg_cnt;
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>> + __le32 msg_len;
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>> +} __attribute__((packed));
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>> +
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>> enum virtio_vsock_type {
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>> VIRTIO_VSOCK_TYPE_STREAM = 1,
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>> + VIRTIO_VSOCK_TYPE_SEQPACKET = 2,
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>> };
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>>
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>> enum virtio_vsock_op {
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>> @@ -83,6 +89,11 @@ enum virtio_vsock_op {
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>> VIRTIO_VSOCK_OP_CREDIT_UPDATE = 6,
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>> /* Request the peer to send the credit info to us */
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>> VIRTIO_VSOCK_OP_CREDIT_REQUEST = 7,
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>> +
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>> + /* Record begin for SOCK_SEQPACKET */
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>> + VIRTIO_VSOCK_OP_SEQ_BEGIN = 8,
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>> + /* Record end for SOCK_SEQPACKET */
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>> + VIRTIO_VSOCK_OP_SEQ_END = 9,
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>> };
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>>
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>> /* VIRTIO_VSOCK_OP_SHUTDOWN flags values */
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>> @@ -91,4 +102,9 @@ enum virtio_vsock_shutdown {
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>> VIRTIO_VSOCK_SHUTDOWN_SEND = 2,
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>> };
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>>
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>> +/* VIRTIO_VSOCK_OP_RW flags values */
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>> +enum virtio_vsock_rw {
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>> + VIRTIO_VSOCK_RW_EOR = 1,
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>> +};
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>> +
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>> #endif /* _UAPI_LINUX_VIRTIO_VSOCK_H */
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> Probably a good idea to also have a feature bit gating
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> this functionality.
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>
IIUC this also requires some qemu patch, because in current
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implementation of vsock device in qemu, there is no 'set_features'
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callback for such device. This callback will handle guest's write
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to feature register, by calling vhost kernel backend, where this
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bit will be processed by host.
Well patching userspace to make use of a kernel feature
is par for the course, isn't it?
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IMHO I'm not sure that SEQPACKET support needs feature
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bit - it is just two new ops for virtio vsock protocol, and from point
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of view of virtio device it is same as STREAM. May be it is needed
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for cases when client tries to connect to server which doesn't support
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SEQPACKET, so without bit result will be "Connection reset by peer",
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and with such bit client will know that server doesn't support it and
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'socket(SOCK_SEQPACKET)' will return error?
Yes, a better error handling would be one reason to do it like this.
--
MST