linux-kernel - Re: [PATCH v3 17/18] xen/pvcalls: implement write

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Message-ID: <alpine.DEB.2.10.1706131758230.12156@sstabellini-ThinkPad-X260>
Date:   Tue, 13 Jun 2017 18:00:17 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Juergen Gross <jgross@...e.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
        boris.ostrovsky@...cle.com,
        Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v3 17/18] xen/pvcalls: implement write

On Tue, 13 Jun 2017, Juergen Gross wrote:
> On 02/06/17 21:31, Stefano Stabellini wrote:
> > When the other end notifies us that there is data to be written
> > (pvcalls_back_conn_event), increment the io and write counters, and
> > schedule the ioworker.
> > 
> > Implement the write function called by ioworker by reading the data from
> > the data ring, writing it to the socket by calling inet_sendmsg.
> > 
> > Set out_error on error.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> > CC: boris.ostrovsky@...cle.com
> > CC: jgross@...e.com
> > ---
> >  drivers/xen/pvcalls-back.c | 74 +++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 73 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> > index e7d2b85..fe3e70f 100644
> > --- a/drivers/xen/pvcalls-back.c
> > +++ b/drivers/xen/pvcalls-back.c
> > @@ -180,7 +180,66 @@ static void pvcalls_conn_back_read(unsigned long opaque)
> >  
> >  static int pvcalls_conn_back_write(struct sock_mapping *map)
> >  {
> > -	return 0;
> > +	struct pvcalls_data_intf *intf = map->ring;
> > +	struct pvcalls_data *data = &map->data;
> > +	struct msghdr msg;
> > +	struct kvec vec[2];
> > +	RING_IDX cons, prod, size, ring_size;
> > +	int ret;
> > +
> > +	cons = intf->out_cons;
> > +	prod = intf->out_prod;
> > +	/* read the indexes before dealing with the data */
> > +	virt_mb();
> > +
> > +	ring_size = XEN_FLEX_RING_SIZE(map->ring_order);
> > +	size = pvcalls_queued(prod, cons, ring_size);
> > +	if (size == 0)
> > +		return 0;
> > +
> > +	memset(&msg, 0, sizeof(msg));
> > +	msg.msg_flags |= MSG_DONTWAIT;
> > +	msg.msg_iter.type = ITER_KVEC|READ;
> > +	msg.msg_iter.count = size;
> > +	if (pvcalls_mask(prod, ring_size) > pvcalls_mask(cons, ring_size)) {
> > +		vec[0].iov_base = data->out + pvcalls_mask(cons, ring_size);
> > +		vec[0].iov_len = size;
> > +		msg.msg_iter.kvec = vec;
> > +		msg.msg_iter.nr_segs = 1;
> > +	} else {
> > +		vec[0].iov_base = data->out + pvcalls_mask(cons, ring_size);
> > +		vec[0].iov_len = ring_size - pvcalls_mask(cons, ring_size);
> > +		vec[1].iov_base = data->out;
> > +		vec[1].iov_len = size - vec[0].iov_len;
> > +		msg.msg_iter.kvec = vec;
> > +		msg.msg_iter.nr_segs = 2;
> > +	}
> > +
> > +	atomic_set(&map->write, 0);
> > +	ret = inet_sendmsg(map->sock, &msg, size);
> > +	if (ret == -EAGAIN || ret < size) {
> 
> Do you really want to do this for all errors?
> Or did you mean:
> 	if ((ret >= 0 && ret < size) || ret == -EAGAIN)

Yes, that's what I meant, thanks!


> > +		atomic_inc(&map->write);
> > +		atomic_inc(&map->io);
> > +	}
> > +	if (ret == -EAGAIN)
> > +		return ret;
> > +
> > +	/* write the data, then update the indexes */
> > +	virt_wmb();
> > +	if (ret < 0) {
> > +		intf->out_error = ret;
> > +	} else {
> > +		intf->out_error = 0;
> > +		intf->out_cons = cons + ret;
> > +		prod = intf->out_prod;
> > +	}
> > +	/* update the indexes, then notify the other end */
> > +	virt_wmb();
> > +	if (prod != cons + ret)
> > +		atomic_inc(&map->write);
> > +	notify_remote_via_irq(map->irq);
> > +
> > +	return ret;
> >  }
> >  
> >  static void pvcalls_back_ioworker(struct work_struct *work)
> > @@ -837,6 +896,19 @@ static irqreturn_t pvcalls_back_event(int irq, void *dev_id)
> >  
> >  static irqreturn_t pvcalls_back_conn_event(int irq, void *sock_map)
> >  {
> > +	struct sock_mapping *map = sock_map;
> > +	struct pvcalls_ioworker *iow;
> > +
> > +	if (map == NULL || map->sock == NULL || map->sock->sk == NULL ||
> > +		map->sock->sk->sk_user_data != map)
> > +		return IRQ_HANDLED;
> > +
> > +	iow = &map->ioworker;
> > +
> > +	atomic_inc(&map->write);
> > +	atomic_inc(&map->io);
> > +	queue_work_on(iow->cpu, iow->wq, &iow->register_work);
> > +
> >  	return IRQ_HANDLED;
> >  }
> >  
> > 
>