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Message-ID: <bbn4lvdwh42m2zvi3rdyws66y5ulew32rchtz3kxirqlllkr63@7toa4tcepax3>
Date: Wed, 21 May 2025 10:57:13 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Xuewei Niu <niuxuewei97@...il.com>
Cc: davem@...emloft.net, fupan.lfp@...group.com, jasowang@...hat.com,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org, mst@...hat.com,
niuxuewei.nxw@...group.com, pabeni@...hat.com, stefanha@...hat.com,
virtualization@...ts.linux.dev, xuanzhuo@...ux.alibaba.com
Subject: Re: [PATCH 2/3] vsock/virtio: Add SIOCINQ support for all virtio
based transports
On Wed, May 21, 2025 at 10:06:13AM +0800, Xuewei Niu wrote:
>> On Mon, May 19, 2025 at 03:06:48PM +0800, Xuewei Niu wrote:
>> >The virtio_vsock_sock has a new field called bytes_unread as the return
>> >value of the SIOCINQ ioctl.
>> >
>> >Though the rx_bytes exists, we introduce a bytes_unread field to the
>> >virtio_vsock_sock struct. The reason is that it will not be updated
>> >until the skbuff is fully consumed, which causes inconsistency.
>> >
>> >The byte_unread is increased by the length of the skbuff when skbuff is
>> >enqueued, and it is decreased when dequeued.
>> >
>> >Signed-off-by: Xuewei Niu <niuxuewei.nxw@...group.com>
>> >---
>> > drivers/vhost/vsock.c | 1 +
>> > include/linux/virtio_vsock.h | 2 ++
>> > net/vmw_vsock/virtio_transport.c | 1 +
>> > net/vmw_vsock/virtio_transport_common.c | 17 +++++++++++++++++
>> > net/vmw_vsock/vsock_loopback.c | 1 +
>> > 5 files changed, 22 insertions(+)
>> >
>> >diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>> >index 802153e23073..0f20af6e5036 100644
>> >--- a/drivers/vhost/vsock.c
>> >+++ b/drivers/vhost/vsock.c
>> >@@ -452,6 +452,7 @@ static struct virtio_transport vhost_transport = {
>> > .notify_set_rcvlowat = virtio_transport_notify_set_rcvlowat,
>> >
>> > .unsent_bytes = virtio_transport_unsent_bytes,
>> >+ .unread_bytes = virtio_transport_unread_bytes,
>> >
>> > .read_skb = virtio_transport_read_skb,
>> > },
>> >diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>> >index 0387d64e2c66..0a7bd240113a 100644
>> >--- a/include/linux/virtio_vsock.h
>> >+++ b/include/linux/virtio_vsock.h
>> >@@ -142,6 +142,7 @@ struct virtio_vsock_sock {
>> > u32 buf_alloc;
>> > struct sk_buff_head rx_queue;
>> > u32 msg_count;
>> >+ size_t bytes_unread;
>>
>> Can we just use `rx_bytes` field we already have?
>>
>> Thanks,
>> Stefano
>
>I perfer not. The `rx_bytes` won't be updated until the skbuff is fully
>consumed, causing inconsistency issues. If it is acceptable to you, I'll
>reuse the field instead.
I think here we found a little pre-existing issue that should be related
also to what Arseniy (CCed) is trying to fix (low_rx_bytes).
We basically have 2 counters:
- rx_bytes, which we use internally to see if there are bytes to read
and for sock_rcvlowat
- fwd_cnt, which we use instead for the credit mechanism and informing
the other peer whether we have space or not
These are updated with virtio_transport_dec_rx_pkt() and
virtio_transport_inc_rx_pkt()
As far as I can see, from the beginning, we call
virtio_transport_dec_rx_pkt() only when we consume the entire packet.
This makes sense for `fwd_cnt`, because we still have occupied space in
memory and we don't want to update the credit until we free all the
space, but I think it makes no sense for `rx_bytes`, which is only used
internally and should reflect the current situation of bytes to read.
So in my opinion we should fix it this way (untested):
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 11eae88c60fc..ee70cb114328 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -449,10 +449,10 @@ static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
}
static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
- u32 len)
+ u32 bytes_read, u32 bytes_dequeued)
{
- vvs->rx_bytes -= len;
- vvs->fwd_cnt += len;
+ vvs->rx_bytes -= bytes_read;
+ vvs->fwd_cnt += bytes_dequeued;
}
void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct sk_buff *skb)
@@ -581,11 +581,11 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
size_t len)
{
struct virtio_vsock_sock *vvs = vsk->trans;
- size_t bytes, total = 0;
struct sk_buff *skb;
u32 fwd_cnt_delta;
bool low_rx_bytes;
int err = -EFAULT;
+ size_t total = 0;
u32 free_space;
spin_lock_bh(&vvs->rx_lock);
@@ -597,6 +597,8 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
}
while (total < len && !skb_queue_empty(&vvs->rx_queue)) {
+ size_t bytes, dequeued = 0;
+
skb = skb_peek(&vvs->rx_queue);
bytes = min_t(size_t, len - total,
@@ -620,12 +622,12 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
VIRTIO_VSOCK_SKB_CB(skb)->offset += bytes;
if (skb->len == VIRTIO_VSOCK_SKB_CB(skb)->offset) {
- u32 pkt_len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
-
- virtio_transport_dec_rx_pkt(vvs, pkt_len);
+ dequeued = le32_to_cpu(virtio_vsock_hdr(skb)->len);
__skb_unlink(skb, &vvs->rx_queue);
consume_skb(skb);
}
+
+ virtio_transport_dec_rx_pkt(vvs, bytes, dequeued);
}
fwd_cnt_delta = vvs->fwd_cnt - vvs->last_fwd_cnt;
@@ -782,7 +784,7 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
msg->msg_flags |= MSG_EOR;
}
- virtio_transport_dec_rx_pkt(vvs, pkt_len);
+ virtio_transport_dec_rx_pkt(vvs, pkt_len, pkt_len);
vvs->bytes_unread -= pkt_len;
kfree_skb(skb);
}
@@ -1752,6 +1754,7 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
struct sock *sk = sk_vsock(vsk);
struct virtio_vsock_hdr *hdr;
struct sk_buff *skb;
+ u32 pkt_len;
int off = 0;
int err;
@@ -1769,7 +1772,8 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOM)
vvs->msg_count--;
- virtio_transport_dec_rx_pkt(vvs, le32_to_cpu(hdr->len));
+ pkt_len = le32_to_cpu(hdr->len);
+ virtio_transport_dec_rx_pkt(vvs, pkt_len, pkt_len);
spin_unlock_bh(&vvs->rx_lock);
virtio_transport_send_credit_update(vsk);
@Arseniy WDYT?
I will test it and send a proper patch.
@Xuewei with that fixed, I think you can use `rx_bytes`, right?
Also because you missed for example `virtio_transport_read_skb()` used
by ebpf (see commit 3543152f2d33 ("vsock: Update rx_bytes on
read_skb()")).
Thanks,
Stefano
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