The code piece which would attach a frag to &xdp_buff is almost
identical across the drivers supporting XDP multi-buffer on Rx.
Make it a generic elegant "oneliner".
Also, I see lots of drivers calculating frags_truesize as
`xdp->frame_sz * nr_frags`. I can't say this is fully correct, since
frags might be backed by chunks of different sizes, especially with
stuff like the header split. Even page_pool_alloc() can give you two
different truesizes on two subsequent requests to allocate the same
buffer size. Add a field to &skb_shared_info (unionized as there's no
free slot currently on x86_64) to track the "true" truesize. It can
be used later when updating the skb.
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
---
include/linux/skbuff.h | 16 +++++--
include/net/xdp.h | 96 +++++++++++++++++++++++++++++++++++++++++-
net/core/xdp.c | 11 +++++
3 files changed, 118 insertions(+), 5 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index b2509cd0b930..bb2b751d274a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -608,11 +608,19 @@ struct skb_shared_info {
* Warning : all fields before dataref are cleared in __alloc_skb()
*/
atomic_t dataref;
- unsigned int xdp_frags_size;
- /* Intermediate layers must ensure that destructor_arg
- * remains valid until skb destructor */
- void * destructor_arg;
+ union {
+ struct {
+ u32 xdp_frags_size;
+ u32 xdp_frags_truesize;
+ };
+
+ /*
+ * 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];
diff --git a/include/net/xdp.h b/include/net/xdp.h
index d2089cfecefd..11139c210b49 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -167,6 +167,93 @@ xdp_get_buff_len(const struct xdp_buff *xdp)
return len;
}
+void xdp_return_frag(netmem_ref netmem, const struct xdp_buff *xdp);
+
+/**
+ * __xdp_buff_add_frag - attach frag to &xdp_buff
+ * @xdp: XDP buffer to attach the frag to
+ * @netmem: network memory containing the frag
+ * @offset: offset at which the frag starts
+ * @size: size of the frag
+ * @truesize: total memory size occupied by the frag
+ * @try_coalesce: whether to try coalescing the frags (not valid for XSk)
+ *
+ * Attach frag to the XDP buffer. If it currently has no frags attached,
+ * initialize the related fields, otherwise check that the frag number
+ * didn't reach the limit of ``MAX_SKB_FRAGS``. If possible, try coalescing
+ * the frag with the previous one.
+ * The function doesn't check/update the pfmemalloc bit. Please use the
+ * non-underscored wrapper in drivers.
+ *
+ * Return: true on success, false if there's no space for the frag in
+ * the shared info struct.
+ */
+static inline bool __xdp_buff_add_frag(struct xdp_buff *xdp, netmem_ref netmem,
+ u32 offset, u32 size, u32 truesize,
+ bool try_coalesce)
+{
+ struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
+ skb_frag_t *prev;
+ u32 nr_frags;
+
+ if (!xdp_buff_has_frags(xdp)) {
+ xdp_buff_set_frags_flag(xdp);
+
+ nr_frags = 0;
+ sinfo->xdp_frags_size = 0;
+ sinfo->xdp_frags_truesize = 0;
+
+ goto fill;
+ }
+
+ nr_frags = sinfo->nr_frags;
+ prev = &sinfo->frags[nr_frags - 1];
+
+ if (try_coalesce && netmem == skb_frag_netmem(prev) &&
+ offset == skb_frag_off(prev) + skb_frag_size(prev)) {
+ skb_frag_size_add(prev, size);
+ /* Guaranteed to only decrement the refcount */
+ xdp_return_frag(netmem, xdp);
+ } else if (unlikely(nr_frags == MAX_SKB_FRAGS)) {
+ return false;
+ } else {
+fill:
+ __skb_fill_netmem_desc_noacc(sinfo, nr_frags++, netmem,
+ offset, size);
+ }
+
+ sinfo->nr_frags = nr_frags;
+ sinfo->xdp_frags_size += size;
+ sinfo->xdp_frags_truesize += truesize;
+
+ return true;
+}
+
+/**
+ * xdp_buff_add_frag - attach frag to &xdp_buff
+ * @xdp: XDP buffer to attach the frag to
+ * @netmem: network memory containing the frag
+ * @offset: offset at which the frag starts
+ * @size: size of the frag
+ * @truesize: total memory size occupied by the frag
+ *
+ * Version of __xdp_buff_add_frag() which takes care of the pfmemalloc bit.
+ *
+ * Return: true on success, false if there's no space for the frag in
+ * the shared info struct.
+ */
+static inline bool xdp_buff_add_frag(struct xdp_buff *xdp, netmem_ref netmem,
+ u32 offset, u32 size, u32 truesize)
+{
+ if (!__xdp_buff_add_frag(xdp, netmem, offset, size, truesize, true))
+ return false;
+
+ if (unlikely(netmem_is_pfmemalloc(netmem)))
+ xdp_buff_set_frag_pfmemalloc(xdp);
+
+ return true;
+}
+
struct xdp_frame {
void *data;
u32 len;
@@ -230,7 +317,14 @@ xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags,
unsigned int size, unsigned int truesize,
bool pfmemalloc)
{
- skb_shinfo(skb)->nr_frags = nr_frags;
+ struct skb_shared_info *sinfo = skb_shinfo(skb);
+
+ sinfo->nr_frags = nr_frags;
+ /*
+ * ``destructor_arg`` is unionized with ``xdp_frags_{,true}size``,
+ * reset it after that these fields aren't used anymore.
+ */
+ sinfo->destructor_arg = NULL;
skb->len += size;
skb->data_len += size;
diff --git a/net/core/xdp.c b/net/core/xdp.c
index f1165a35411b..a66a4e036f53 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -535,6 +535,17 @@ void xdp_return_frame_bulk(struct xdp_frame *xdpf,
}
EXPORT_SYMBOL_GPL(xdp_return_frame_bulk);
+/**
+ * xdp_return_frag -- free one XDP frag or decrement its refcount
+ * @netmem: network memory reference to release
+ * @xdp: &xdp_buff to release the frag for
+ */
+void xdp_return_frag(netmem_ref netmem, const struct xdp_buff *xdp)
+{
+ __xdp_return(netmem, xdp->rxq->mem.type, true, NULL);
+}
+EXPORT_SYMBOL_GPL(xdp_return_frag);
+
void xdp_return_buff(struct xdp_buff *xdp)
{
struct skb_shared_info *sinfo;
--
2.47.1
