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Tsirkin" , Jason Wang , "David S. Miller" , Jakub Kicinski , Jorgen Hansen , Norbert Slusarek , Colin Ian King , Andra Paraschiv , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, oxffffaa@gmail.com Subject: Re: [PATCH v10 11/18] virtio/vsock: dequeue callback for SOCK_SEQPACKET Message-ID: <20210603144513.ryjzauq7abnjogu3@steredhat> References: <20210520191357.1270473-1-arseny.krasnov@kaspersky.com> <20210520191801.1272027-1-arseny.krasnov@kaspersky.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20210520191801.1272027-1-arseny.krasnov@kaspersky.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, May 20, 2021 at 10:17:58PM +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 >--- > v9 -> v10: > 1) Number of dequeued bytes incremented even in case when > user's buffer is full. > 2) Use 'msg_data_left()' instead of direct access to 'msg_hdr'. > 3) Rename variable 'err' to 'dequeued_len', in case of error > it has negative value. > > include/linux/virtio_vsock.h | 5 ++ > net/vmw_vsock/virtio_transport_common.c | 65 +++++++++++++++++++++++++ > 2 files changed, 70 insertions(+) > >diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h >index dc636b727179..02acf6e9ae04 100644 >--- a/include/linux/virtio_vsock.h >+++ b/include/linux/virtio_vsock.h >@@ -80,6 +80,11 @@ 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, >+ bool *msg_ready); > 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..61349b2ea7fe 100644 >--- a/net/vmw_vsock/virtio_transport_common.c >+++ b/net/vmw_vsock/virtio_transport_common.c >@@ -393,6 +393,59 @@ 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, >+ bool *msg_ready) >+{ >+ 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); >+ >+ *msg_ready = false; >+ spin_lock_bh(&vvs->rx_lock); >+ >+ while (!*msg_ready && !list_empty(&vvs->rx_queue) && dequeued_len >= 0) { I' >+ size_t bytes_to_copy; >+ size_t pkt_len; >+ >+ pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list); >+ pkt_len = (size_t)le32_to_cpu(pkt->hdr.len); >+ bytes_to_copy = min(user_buf_len, pkt_len); >+ >+ if (bytes_to_copy) { >+ /* 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); >+ >+ if (memcpy_to_msg(msg, pkt->buf, bytes_to_copy)) >+ dequeued_len = -EINVAL; I think here is better to return the error returned by memcpy_to_msg(), as we do in the other place where we use memcpy_to_msg(). I mean something like this: err = memcpy_to_msgmsg, pkt->buf, bytes_to_copy); if (err) dequeued_len = err; >+ else >+ user_buf_len -= bytes_to_copy; >+ >+ spin_lock_bh(&vvs->rx_lock); >+ } >+ Maybe here we can simply break the cycle if we have an error: if (dequeued_len < 0) break; Or we can refactor a bit, simplifying the while() condition and also the code in this way (not tested): while (!*msg_ready && !list_empty(&vvs->rx_queue)) { ... if (bytes_to_copy) { int err; /* ... */ spin_unlock_bh(&vvs->rx_lock); err = memcpy_to_msgmsg, pkt->buf, bytes_to_copy); if (err) { dequeued_len = err; goto out; } spin_lock_bh(&vvs->rx_lock); user_buf_len -= bytes_to_copy; } dequeued_len += pkt_len; if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOR) *msg_ready = true; virtio_transport_dec_rx_pkt(vvs, pkt); list_del(&pkt->list); virtio_transport_free_pkt(pkt); } out: spin_unlock_bh(&vvs->rx_lock); virtio_transport_send_credit_update(vsk); return dequeued_len; }