Re: [Xen-devel] [PATCH 4/7] xen/9pfs: connect to the backend

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 7 Mar 2017, Boris Ostrovsky wrote:
> > +static int xen_9pfs_front_free(struct xen_9pfs_front_priv *priv)
> > +{
> > +   int i, j;
> > +
> > +   list_del(&priv->list);
> > +
> > +   for (i = 0; i < priv->num_rings; i++) {
> > +           if (priv->rings[i].intf == NULL)
> > +                   break;
> 
> Are we guaranteed that all subsequent entries are not allocated (i.e.
> this shouldn't be 'continue')?

Yes, we are guaranteed that all subsequent entries are NULL because they
are allocated in order until an error occurs.


> > +           if (priv->rings[i].irq > 0)
> > +                   unbind_from_irqhandler(priv->rings[i].irq, priv->dev);
> > +           if (priv->rings[i].bytes != NULL) {
> > +                   for (j = 0; j < (1 << XEN_9PFS_RING_ORDER); j++)
> > +                           
> > gnttab_end_foreign_access(priv->rings[i].intf->ref[j], 0, 0);
> > +                   free_pages((unsigned long)priv->rings[i].bytes, 
> > XEN_9PFS_RING_ORDER);
> > +           }
> > +           gnttab_end_foreign_access(priv->rings[i].ref, 0, 0);
> > +           free_page((unsigned long)priv->rings[i].intf);
> > +   }
> > +   kfree(priv->rings);
> > +   kfree(priv);
> > +
> > +   return 0;
> > +}
> > +
> >  static int xen_9pfs_front_remove(struct xenbus_device *dev)
> >  {
> > +   int ret;
> > +   struct xen_9pfs_front_priv *priv = dev_get_drvdata(&dev->dev);
> > +
> > +   dev_set_drvdata(&dev->dev, NULL);
> > +   ret = xen_9pfs_front_free(priv);
> > +   return ret;
> > +}
> > +
> > +static int xen_9pfs_front_alloc_dataring(struct xenbus_device *dev,
> > +           struct xen_9pfs_dataring *ring)
> > +{
> > +   int i;
> > +   int ret = -ENOMEM;
> > +
> > +   init_waitqueue_head(&ring->wq);
> > +   spin_lock_init(&ring->lock);
> > +   INIT_WORK(&ring->work, p9_xen_response);
> > +
> > +   ring->intf = (struct xen_9pfs_data_intf *) __get_free_page(GFP_KERNEL | 
> > __GFP_ZERO);
> > +   if (!ring->intf)
> > +           goto error;
> > +   memset(ring->intf, 0, XEN_PAGE_SIZE);
> 
> get_zeroed_page()?  (especially given that __get_free_page() returns
> PAGE_SIZE, not XEN_PAGE_SIZE)

Yes, good point.


 
> > +   ring->bytes = (void*)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 
> > XEN_9PFS_RING_ORDER);
> > +   if (ring->bytes == NULL)
> > +           goto error;
> > +   for (i = 0; i < (1 << XEN_9PFS_RING_ORDER); i++)
> > +           ring->intf->ref[i] = 
> > gnttab_grant_foreign_access(dev->otherend_id, 
> > pfn_to_gfn(virt_to_pfn((void*)ring->bytes) + i), 0);
> > +   ring->ref = gnttab_grant_foreign_access(dev->otherend_id, 
> > pfn_to_gfn(virt_to_pfn((void*)ring->intf)), 0);
> > +   ring->ring.in = ring->bytes;
> > +   ring->ring.out = ring->bytes + XEN_9PFS_RING_SIZE;
> > +
> > +   ret = xenbus_alloc_evtchn(dev, &ring->evtchn);
> > +   if (ret)
> > +           goto error;
> > +   ring->irq = bind_evtchn_to_irqhandler(ring->evtchn, 
> > xen_9pfs_front_event_handler,
> > +                                   0, "xen_9pfs-frontend", ring);
> > +   if (ring->irq < 0) {
> > +           xenbus_free_evtchn(dev, ring->evtchn);
> > +           ret = ring->irq;
> > +           goto error;
> > +   }
> >     return 0;
> > +
> > +error:
> 
> You may need to gnttab_end_foreign_access().

Actually this error path is unnecessary because it will be handled by
xen_9pfs_front_probe, that calls xen_9pfs_front_free on errors. I'll
remove it.


> > +   if (ring->intf != NULL)
> > +           kfree(ring->intf);
> > +   if (ring->bytes != NULL)
> > +           kfree(ring->bytes);
> > +   return ret;
> >  }
> >  
> >  static int xen_9pfs_front_probe(struct xenbus_device *dev,
> >             const struct xenbus_device_id *id)
> >  {
> > +   int ret = -EFAULT, i;
> 
> Unnecessary initialization.

I'll remove it.


> > +   struct xenbus_transaction xbt;
> > +   struct xen_9pfs_front_priv *priv = NULL;
> > +   char *versions;
> > +   unsigned int max_rings, max_ring_order, len;
> > +
> > +   versions = xenbus_read(XBT_NIL, dev->otherend, "versions", &len);
> > +   if (!len || strcmp(versions, "1"))
> > +           return -EINVAL;
> > +   kfree(versions);
> > +   ret = xenbus_scanf(XBT_NIL, dev->otherend, "max-rings", "%u", 
> > &max_rings);
> > +   if (ret < 0 || max_rings < XEN_9PFS_NUM_RINGS)
> > +           return -EINVAL;
> > +   ret = xenbus_scanf(XBT_NIL, dev->otherend, "max-ring-page-order", "%u", 
> > &max_ring_order);
> > +   if (ret < 0|| max_ring_order < XEN_9PFS_RING_ORDER)
> > +           return -EINVAL;
> > +
> > +
> > +   priv = kzalloc(sizeof(struct xen_9pfs_front_priv), GFP_KERNEL);
> > +   if (!priv)
> > +           return -ENOMEM;
> > +
> > +   priv->dev = dev;
> > +   priv->num_rings = XEN_9PFS_NUM_RINGS;
> > +   priv->rings = kzalloc(sizeof(struct xen_9pfs_dataring) * 
> > priv->num_rings,
> > +                                           GFP_KERNEL);
> > +   if (!priv->rings) {
> > +           kfree(priv);
> > +           return -ENOMEM;
> > +   }
> > +
> > + again:
> > +   ret = xenbus_transaction_start(&xbt);
> > +   if (ret) {
> > +           xenbus_dev_fatal(dev, ret, "starting transaction");
> > +           goto error;
> > +   }
> > +   ret = xenbus_printf(xbt, dev->nodename, "version", "%u", 1);
> > +   if (ret)
> > +           goto error_xenbus;
> > +   ret = xenbus_printf(xbt, dev->nodename, "num-rings", "%u", 
> > priv->num_rings);
> > +   if (ret)
> > +           goto error_xenbus;
> > +   for (i = 0; i < priv->num_rings; i++) {
> > +           char str[16];
> > +
> > +           priv->rings[i].priv = priv;
> > +           ret = xen_9pfs_front_alloc_dataring(dev, &priv->rings[i]);
> 
> Not for -EAGAIN, I think.

I don't think xen_9pfs_front_alloc_dataring can return EAGAIN. EAGAIN
can only come from xenbus_transaction_end, the case we handle below.


> > +           if (ret < 0)
> > +                   goto error_xenbus;
> > +
> > +           sprintf(str, "ring-ref%u", i);
> > +           ret = xenbus_printf(xbt, dev->nodename, str, "%d", 
> > priv->rings[i].ref);
> > +           if (ret)
> > +                   goto error_xenbus;
> > +
> > +           sprintf(str, "event-channel-%u", i);
> > +           ret = xenbus_printf(xbt, dev->nodename, str, "%u", 
> > priv->rings[i].evtchn);
> > +           if (ret)
> > +                   goto error_xenbus;
> > +   }
> > +   priv->tag = xenbus_read(xbt, dev->nodename, "tag", NULL);
> > +   if (ret)
> > +           goto error_xenbus;
> > +   ret = xenbus_transaction_end(xbt, 0);
> > +   if (ret) {
> > +           if (ret == -EAGAIN)
> > +                   goto again;
> > +           xenbus_dev_fatal(dev, ret, "completing transaction");
> > +           goto error;
> > +   }
> > +
> > +
> > +   list_add_tail(&priv->list, &xen_9pfs_devs);
> > +   dev_set_drvdata(&dev->dev, priv);
> > +   xenbus_switch_state(dev, XenbusStateInitialised);
> > +
> >     return 0;
> > +
> > + error_xenbus:
> > +   xenbus_transaction_end(xbt, 1);
> > +   xenbus_dev_fatal(dev, ret, "writing xenstore");
> > + error:
> > +   dev_set_drvdata(&dev->dev, NULL);
> > +   xen_9pfs_front_free(priv);
> > +   return ret;
> >  }
> >  
> 

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