Messages in this thread | | | Date | Fri, 18 Jun 2021 17:55:55 +0200 | From | Stefano Garzarella <> | Subject | Re: [PATCH v11 11/18] virtio/vsock: dequeue callback for SOCK_SEQPACKET |
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On Fri, Jun 18, 2021 at 06:04:37PM +0300, Arseny Krasnov wrote: > >On 18.06.2021 16:44, Stefano Garzarella wrote: >> Hi Arseny, >> the series looks great, I have just a question below about >> seqpacket_dequeue. >> >> I also sent a couple a simple fixes, it would be great if you can review >> them: >> https://lore.kernel.org/netdev/20210618133526.300347-1-sgarzare@redhat.com/ >> >> >> On Fri, Jun 11, 2021 at 02:12:38PM +0300, Arseny Krasnov wrote: >>> Callback fetches RW packets from rx queue of socket until whole record >>> is copied(if user's buffer is full, user is not woken up). This is done >>> to not stall sender, because if we wake up user and it leaves syscall, >>> nobody will send credit update for rest of record, and sender will wait >>> for next enter of read syscall at receiver's side. So if user buffer is >>> full, we just send credit update and drop data. >>> >>> Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com> >>> --- >>> v10 -> v11: >>> 1) 'msg_count' field added to count current number of EORs. >>> 2) 'msg_ready' argument removed from callback. >>> 3) If 'memcpy_to_msg()' failed during copy loop, there will be >>> no next attempts to copy data, rest of record will be freed. >>> >>> include/linux/virtio_vsock.h | 5 ++ >>> net/vmw_vsock/virtio_transport_common.c | 84 +++++++++++++++++++++++++ >>> 2 files changed, 89 insertions(+) >>> >>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h >>> index dc636b727179..1d9a302cb91d 100644 >>> --- a/include/linux/virtio_vsock.h >>> +++ b/include/linux/virtio_vsock.h >>> @@ -36,6 +36,7 @@ struct virtio_vsock_sock { >>> u32 rx_bytes; >>> u32 buf_alloc; >>> struct list_head rx_queue; >>> + u32 msg_count; >>> }; >>> >>> struct virtio_vsock_pkt { >>> @@ -80,6 +81,10 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk, >>> struct msghdr *msg, >>> size_t len, int flags); >>> >>> +ssize_t >>> +virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk, >>> + struct msghdr *msg, >>> + int flags); >>> s64 virtio_transport_stream_has_data(struct vsock_sock *vsk); >>> s64 virtio_transport_stream_has_space(struct vsock_sock *vsk); >>> >>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c >>> index ad0d34d41444..1e1df19ec164 100644 >>> --- a/net/vmw_vsock/virtio_transport_common.c >>> +++ b/net/vmw_vsock/virtio_transport_common.c >>> @@ -393,6 +393,78 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk, >>> return err; >>> } >>> >>> +static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk, >>> + struct msghdr *msg, >>> + int flags) >>> +{ >>> + struct virtio_vsock_sock *vvs = vsk->trans; >>> + struct virtio_vsock_pkt *pkt; >>> + int dequeued_len = 0; >>> + size_t user_buf_len = msg_data_left(msg); >>> + bool copy_failed = false; >>> + bool msg_ready = false; >>> + >>> + spin_lock_bh(&vvs->rx_lock); >>> + >>> + if (vvs->msg_count == 0) { >>> + spin_unlock_bh(&vvs->rx_lock); >>> + return 0; >>> + } >>> + >>> + while (!msg_ready) { >>> + pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list); >>> + >>> + if (!copy_failed) { >>> + size_t pkt_len; >>> + size_t bytes_to_copy; >>> + >>> + pkt_len = (size_t)le32_to_cpu(pkt->hdr.len); >>> + bytes_to_copy = min(user_buf_len, pkt_len); >>> + >>> + if (bytes_to_copy) { >>> + int err; >>> + >>> + /* sk_lock is held by caller so no one else can dequeue. >>> + * Unlock rx_lock since memcpy_to_msg() may sleep. >>> + */ >>> + spin_unlock_bh(&vvs->rx_lock); >>> + >>> + err = memcpy_to_msg(msg, pkt->buf, bytes_to_copy); >>> + if (err) { >>> + /* Copy of message failed, set flag to skip >>> + * copy path for rest of fragments. Rest of >>> + * fragments will be freed without copy. >>> + */ >>> + copy_failed = true; >>> + dequeued_len = err; >> If we fail to copy the message we will discard the entire packet. >> Is it acceptable for the user point of view, or we should leave the >> packet in the queue and the user can retry, maybe with a different >> buffer? >> >> Then we can remove the packets only when we successfully copied all the >> fragments. >> >> I'm not sure make sense, maybe better to check also other >> implementations :-) >> >> Thanks, >> Stefano > >Understand, i'll check it on weekend, anyway I think it is >not critical for implementation.
Yep, I agree.
> > >I have another question: may be it is useful to research for >approach where packets are not queued until whole message >is received, but copied to user's buffer thus freeing memory. >(like previous implementation, of course with solution of problem >where part of message still in queue, while reader was woken >by timeout or signal). > >I think it is better, because in current version, sender may set >'peer_alloc_buf' to for example 1MB, so at receiver we get >1MB of 'kmalloc()' memory allocated, while having user's buffer >to copy data there or drop it(if user's buffer is full). This way >won't change spec(e.g. no message id or SEQ_BEGIN will be added). > >What do You think?
Yep, I see your point and it would be great, but I think the main issues to fix is how to handle a signal while we are waiting other fragments since the other peer can take unspecified time to send them.
Note that the 'peer_alloc_buf' in the sender, is the value get from the receiver, so if the receiver doesn't want to allocate 1MB, can advertise a small buffer size.
Thanks, Stefano
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