Messages in this thread | | | Date | Fri, 18 Jun 2021 18:25:09 +0200 | From | Stefano Garzarella <> | Subject | Re: [MASSMAIL KLMS] Re: [PATCH v11 11/18] virtio/vsock: dequeue callback for SOCK_SEQPACKET |
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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@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. > >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
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