[RFC PATCH V2 3/5] Add userspace buffers callback in skb_share_info

[Shirley Ma]

Signed-off-by: Shirley Ma <x...@us.ibm.com>
---

 include/linux/skbuff.h |   13 +++++++++++++
 net/core/skbuff.c      |   13 ++++++++++++-
 2 files changed, 25 insertions(+), 1 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index e6ba898..938a7cb 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -183,6 +183,15 @@ enum {
        SKBTX_DRV_NEEDS_SK_REF = 1 << 3,
 };
 
+/* The callback notifies userspace to release buffers when skb DMA is done in
+ * lower device, the desc is used to track userspace buffer index.
+ */
+struct skb_ubuf_info {
+       /* support buffers allocation from userspace */
+       void            (*callback)(struct sk_buff *);
+       size_t          desc;
+};
+
 /* This data is invariant across clones and lives at
  * the end of the header data, ie. at skb->end.
  */
@@ -205,6 +214,10 @@ struct skb_shared_info {
        /* Intermediate layers must ensure that destructor_arg
         * remains valid until skb destructor */
        void *          destructor_arg;
+
+       /* DMA mapping from userspace buffers */
+       struct skb_ubuf_info ubuf;
+
        /* must be last field, see pskb_expand_head() */
        skb_frag_t      frags[MAX_SKB_FRAGS];
 };
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 104f844..f9468a0 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -210,6 +210,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t 
gfp_mask,
        shinfo = skb_shinfo(skb);
        memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
        atomic_set(&shinfo->dataref, 1);
+       shinfo->ubuf.callback = NULL;
 
        if (fclone) {
                struct sk_buff *child = skb + 1;
@@ -329,6 +330,15 @@ static void skb_release_data(struct sk_buff *skb)
 
                if (skb_has_frag_list(skb))
                        skb_drop_fraglist(skb);
+               
+               /*
+                * if skb buf is from userspace, we need to notify the caller
+                * the lower device DMA has done;
+                */
+               if (skb_shinfo(skb)->ubuf.callback) {
+                       skb_shinfo(skb)->ubuf.callback(skb);
+                       skb_shinfo(skb)->ubuf.callback = NULL;
+               }
 
                kfree(skb->head);
        }
@@ -492,6 +502,7 @@ bool skb_recycle_check(struct sk_buff *skb, int skb_size)
        shinfo = skb_shinfo(skb);
        memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
        atomic_set(&shinfo->dataref, 1);
+       shinfo->ubuf.callback = NULL;
 
        memset(skb, 0, offsetof(struct sk_buff, tail));
        skb->data = skb->head + NET_SKB_PAD;



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