On 18.06.2021 19:25, Stefano Garzarella wrote: > On Fri, Jun 18, 2021 at 07:08:30PM +0300, Arseny Krasnov wrote: >> On 18.06.2021 18:55, Stefano Garzarella wrote: >>> 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@xxxxxxxxxx/ >>>>> >>>>> >>>>> 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@xxxxxxxxxxxxx> >>>>>> --- >>>>>> 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. >> What about transport callback, something like 'seqpacket_drain()' or >> >> 'seqpacket_drop_curr()' - when we got signal or timeout, notify transport >> >> to drop current message. In virtio case this will set special flag in transport, >> >> so on next dequeue, this flag is checked and if it is set - we drop all packets >> >> until EOR found. Then we can copy untouched new record. >> > But in this way, we will lose the entire message. > > Is it acceptable for seqpacket? > > Stefano Hm, i'll check it. At least for unix domain sockets - it supports SEQPACKET > >
