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Fri, 18 Jun 2021 08:56:00 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyb8+5HIJLdutX7cENNNI1/ecBZD9YW9aCIcD5DoBeecwsxaAXgeOQAGd3lSOiR1Xdg+NTIjg== X-Received: by 2002:a5d:6d8a:: with SMTP id l10mr13665839wrs.63.1624031760459; Fri, 18 Jun 2021 08:56:00 -0700 (PDT) Received: from steredhat.lan ([5.170.128.175]) by smtp.gmail.com with ESMTPSA id m18sm8968801wmq.45.2021.06.18.08.55.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Jun 2021 08:56:00 -0700 (PDT) Date: Fri, 18 Jun 2021 17:55:55 +0200 From: Stefano Garzarella To: Arseny Krasnov Subject: Re: [PATCH v11 11/18] virtio/vsock: dequeue callback for SOCK_SEQPACKET Message-ID: <20210618155555.j5p4v6j5gk2dboj3@steredhat.lan> References: <20210611110744.3650456-1-arseny.krasnov@kaspersky.com> <20210611111241.3652274-1-arseny.krasnov@kaspersky.com> <20210618134423.mksgnbmchmow4sgh@steredhat.lan> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=sgarzare@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: Andra Paraschiv , "kvm@vger.kernel.org" , "Michael S. Tsirkin" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "oxffffaa@gmail.com" , Norbert Slusarek , Stefan Hajnoczi , Colin Ian King , Jakub Kicinski , "David S. Miller" X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1"; Format="flowed" Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" 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.c= om/ >> >> >> 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 >>> --- >>> 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 *vs= k, >>> 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/vi= rtio_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_so= ck *vsk, >>> return err; >>> } >>> >>> +static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vs= k, >>> + struct msghdr *msg, >>> + int flags) >>> +{ >>> + struct virtio_vsock_sock *vvs =3D vsk->trans; >>> + struct virtio_vsock_pkt *pkt; >>> + int dequeued_len =3D 0; >>> + size_t user_buf_len =3D msg_data_left(msg); >>> + bool copy_failed =3D false; >>> + bool msg_ready =3D false; >>> + >>> + spin_lock_bh(&vvs->rx_lock); >>> + >>> + if (vvs->msg_count =3D=3D 0) { >>> + spin_unlock_bh(&vvs->rx_lock); >>> + return 0; >>> + } >>> + >>> + while (!msg_ready) { >>> + pkt =3D list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, li= st); >>> + >>> + if (!copy_failed) { >>> + size_t pkt_len; >>> + size_t bytes_to_copy; >>> + >>> + pkt_len =3D (size_t)le32_to_cpu(pkt->hdr.len); >>> + bytes_to_copy =3D 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 =3D 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 =3D true; >>> + dequeued_len =3D 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=A0 in current version, sender may set >'peer_alloc_buf' to=A0 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 _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization