Re: [PATCH] xen/netfront: handle compound page fragments on transmit

Tuesday, November 20, 2012, 2:30:54 PM, you wrote:

Aside from Jans comments about error handling, I tried below patch and it seems
to solve the problem with transfers out of the domU for me (though only shallow
testing done, otoh 5 times is more than getting stuck the first time).

-Stefan

I'm running with this patch now, it seems to fix the problems for me as well.

--
Sander

On 20.11.2012 12:40, Ian Campbell wrote:

quoted

An SKB paged fragment can consist of a compound page with order > 0.
However the netchannel protocol deals only in PAGE_SIZE frames.

Handle this in xennet_make_frags by iterating over the frames which
make up the page.

This is the netfront equivalent to 6a8ed462f16b for netback.

Signed-off-by: Ian Campbell <redacted>
Cc: netdev@vger.kernel.org
Cc: xen-devel@lists.xen.org
Cc: Eric Dumazet <redacted>
Cc: Konrad Rzeszutek Wilk <konrad@kernel.org>
Cc: ANNIE LI <redacted>
Cc: Sander Eikelenboom <redacted>
Cc: Stefan Bader <redacted>

Tested-by: Stefan Bader <redacted>

quoted

---
 drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
 1 files changed, 44 insertions(+), 14 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index caa0110..a12b99a 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c

@@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
      /* Grant backend access to each skb fragment page. */
      for (i = 0; i < frags; i++) {
              skb_frag_t *frag = skb_shinfo(skb)->frags + i;
+             struct page *page = skb_frag_page(frag);
+             unsigned long size = skb_frag_size(frag);
+             unsigned long offset = frag->page_offset;
 
-             tx->flags |= XEN_NETTXF_more_data;
+             /* Data must not cross a page boundary. */
+             BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
 
-             id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
-             np->tx_skbs[id].skb = skb_get(skb);
-             tx = RING_GET_REQUEST(&np->tx, prod++);
-             tx->id = id;
-             ref = gnttab_claim_grant_reference(&np->gref_tx_head);
-             BUG_ON((signed short)ref < 0);
+             /* Skip unused frames from start of page */
+             page += offset >> PAGE_SHIFT;
+             offset &= ~PAGE_MASK;
 
-             mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
-             gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
-                                             mfn, GNTMAP_readonly);
+             while (size > 0) {
+                     unsigned long bytes;
 
-             tx->gref = np->grant_tx_ref[id] = ref;
-             tx->offset = frag->page_offset;
-             tx->size = skb_frag_size(frag);
-             tx->flags = 0;
+                     BUG_ON(offset >= PAGE_SIZE);
+
+                     bytes = PAGE_SIZE - offset;
+                     if (bytes > size)
+                             bytes = size;
+
+                     tx->flags |= XEN_NETTXF_more_data;
+
+                     id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
+                     np->tx_skbs[id].skb = skb_get(skb);
+                     tx = RING_GET_REQUEST(&np->tx, prod++);
+                     tx->id = id;
+                     ref = gnttab_claim_grant_reference(&np->gref_tx_head);
+                     BUG_ON((signed short)ref < 0);
+
+                     mfn = pfn_to_mfn(page_to_pfn(page));
+                     gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
+                                                     mfn, GNTMAP_readonly);
+
+                     tx->gref = np->grant_tx_ref[id] = ref;
+                     tx->offset = offset;
+                     tx->size = bytes;
+                     tx->flags = 0;
+
+                     offset += bytes;
+                     size -= bytes;
+
+                     /* Next frame */
+                     if (offset == PAGE_SIZE && size) {
+                             BUG_ON(!PageCompound(page));
+                             page++;
+                             offset = 0;
+                     }
+             }
      }
 
      np->tx.req_prod_pvt = prod;