On 7/6/2011 4:22 PM, Shirley Ma wrote:
This patch adds userspace buffers support in skb shared info. A new
struct skb_ubuf_info is needed to maintain the userspace buffers
argument and index, a callback is used to notify userspace to release
the buffers once lower device has done DMA (Last reference to that skb
has gone).
If there is any userspace apps to reference these userspace buffers,
then these userspaces buffers will be copied into kernel. This way we
can prevent userspace apps from holding these userspace buffers too long.
Use destructor_arg to point to the userspace buffer info; a new tx flags
SKBTX_DEV_ZEROCOPY is added for zero-copy buffer check.
Signed-off-by: Shirley Ma x...@...ibm.com
I was just reading this patch and noticed that you check if
uarg-callback is set before calling it in skb_release_data, but you do
not check before calling it in skb_copy_ubufs.
I was only skimming so I have probably missed something...
---
include/linux/skbuff.h | 16 ++
net/core/skbuff.c | 79
+++-
2 files changed, 94 insertions(+), 1 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 3e54337..08d4507 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -187,6 +187,20 @@ enum {
/* ensure the originating sk reference is available on driver level */
SKBTX_DRV_NEEDS_SK_REF = 1 3,
+
+ /* device driver supports TX zero-copy buffers */
+ SKBTX_DEV_ZEROCOPY = 1 4,
+};
+
+/*
+ * The callback notifies userspace to release buffers when skb DMA is done in
+ * lower device, the skb last reference should be 0 when calling this.
+ * The desc is used to track userspace buffer index.
+ */
+struct ubuf_info {
+ void (*callback)(void *);
+ void *arg;
+ unsigned long desc;
};
/* This data is invariant across clones and lives at
@@ -211,6 +225,7 @@ struct skb_shared_info {
/* Intermediate layers must ensure that destructor_arg
* remains valid until skb destructor */
void * destructor_arg;
+
/* must be last field, see pskb_expand_head() */
skb_frag_t frags[MAX_SKB_FRAGS];
};
@@ -2265,5 +2280,6 @@ static inline void skb_checksum_none_assert(struct
sk_buff *skb)
}
bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);
+
#endif /* __KERNEL__ */
#endif /* _LINUX_SKBUFF_H */
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 46cbd28..42462f5 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -329,6 +329,18 @@ static void skb_release_data(struct sk_buff *skb)
put_page(skb_shinfo(skb)-frags[i].page);
}
+ /*
+ * If skb buf is from userspace, we need to notify the caller
+ * the lower device DMA has done;
+ */
+ if (skb_shinfo(skb)-tx_flags SKBTX_DEV_ZEROCOPY) {
+ struct ubuf_info *uarg;
+
+ uarg = skb_shinfo(skb)-destructor_arg;
+ if (uarg-callback)
+ uarg-callback(uarg);
+ }
+
if (skb_has_frag_list(skb))
skb_drop_fraglist(skb);
@@ -481,6 +493,9 @@ bool skb_recycle_check(struct sk_buff *skb, int skb_size)
if (irqs_disabled())
return false;
+ if (skb_shinfo(skb)-tx_flags SKBTX_DEV_ZEROCOPY)
+ return false;
+
if (skb_is_nonlinear(skb) || skb-fclone != SKB_FCLONE_UNAVAILABLE)
return false;
@@ -596,6 +611,50 @@ struct sk_buff *skb_morph(struct sk_buff *dst, struct
sk_buff *src)
}
EXPORT_SYMBOL_GPL(skb_morph);
+/* skb frags copy userspace buffers to kernel */
+static int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
+{
+ int i;
+ int num_frags = skb_shinfo(skb)-nr_frags;
+ struct page *page, *head = NULL;
+ struct ubuf_info *uarg = skb_shinfo(skb)-destructor_arg;
+
+ for (i = 0; i num_frags; i++) {
+ u8 *vaddr;
+ skb_frag_t *f = skb_shinfo(skb)-frags[i];
+
+ page = alloc_page(GFP_ATOMIC);
+ if (!page) {
+ while (head) {
+ put_page(head);
+ head = (struct page *)head-private;
+ }
+ return -ENOMEM;
+ }
+ vaddr = kmap_skb_frag(skb_shinfo(skb)-frags[i]);
+ memcpy(page_address(page),
+vaddr + f-page_offset, f-size);
+ kunmap_skb_frag(vaddr);
+ page-private = (unsigned long)head;
+ head = page;
+ }
+
+ /* skb frags release userspace buffers */
+ for (i = 0; i skb_shinfo(skb)-nr_frags; i++)
+ put_page(skb_shinfo(skb)-frags[i].page);
+
+ uarg-callback(uarg);
+
+
