[NET]: Zerocopy sequential reading of skb data
Implements sequential reading for both linear and non-linear
skb data at zerocopy cost. The data is returned in chunks of
arbitary length, therefore random access is not possible.
Usage:
from := 0
to := 128
state := undef
data := undef
len := undef
consumed := 0
skb_prepare_seq_read(skb, from, to, &state)
while (len = skb_seq_read(consumed, &data, &state)) != 0 do
/* do something with 'data' of length 'len' */
if abort then
/* abort read if we don't wait for
* skb_seq_read() to return 0 */
skb_abort_seq_read(&state)
return
endif
/* not necessary to consume all of 'len' */
consumed += len
done
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index d7c839a..171a37d 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -321,6 +321,24 @@
extern void skb_under_panic(struct sk_buff *skb, int len,
void *here);
+struct skb_seq_state
+{
+ __u32 lower_offset;
+ __u32 upper_offset;
+ __u32 frag_idx;
+ __u32 stepped_offset;
+ struct sk_buff *root_skb;
+ struct sk_buff *cur_skb;
+ __u8 *frag_data;
+};
+
+extern void skb_prepare_seq_read(struct sk_buff *skb,
+ unsigned int from, unsigned int to,
+ struct skb_seq_state *st);
+extern unsigned int skb_seq_read(unsigned int consumed, const u8 **data,
+ struct skb_seq_state *st);
+extern void skb_abort_seq_read(struct skb_seq_state *st);
+
/* Internal */
#define skb_shinfo(SKB) ((struct skb_shared_info *)((SKB)->end))
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 6d68c03..d285f2f 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1500,6 +1500,120 @@
skb_split_no_header(skb, skb1, len, pos);
}
+/**
+ * skb_prepare_seq_read - Prepare a sequential read of skb data
+ * @skb: the buffer to read
+ * @from: lower offset of data to be read
+ * @to: upper offset of data to be read
+ * @st: state variable
+ *
+ * Initializes the specified state variable. Must be called before
+ * invoking skb_seq_read() for the first time.
+ */
+void skb_prepare_seq_read(struct sk_buff *skb, unsigned int from,
+ unsigned int to, struct skb_seq_state *st)
+{
+ st->lower_offset = from;
+ st->upper_offset = to;
+ st->root_skb = st->cur_skb = skb;
+ st->frag_idx = st->stepped_offset = 0;
+ st->frag_data = NULL;
+}
+
+/**
+ * skb_seq_read - Sequentially read skb data
+ * @consumed: number of bytes consumed by the caller so far
+ * @data: destination pointer for data to be returned
+ * @st: state variable
+ *
+ * Reads a block of skb data at &consumed relative to the
+ * lower offset specified to skb_prepare_seq_read(). Assigns
+ * the head of the data block to &data and returns the length
+ * of the block or 0 if the end of the skb data or the upper
+ * offset has been reached.
+ *
+ * The caller is not required to consume all of the data
+ * returned, i.e. &consumed is typically set to the number
+ * of bytes already consumed and the next call to
+ * skb_seq_read() will return the remaining part of the block.
+ *
+ * Note: The size of each block of data returned can be arbitary,
+ * this limitation is the cost for zerocopy seqeuental
+ * reads of potentially non linear data.
+ *
+ * Note: Fragment lists within fragments are not implemented
+ * at the moment, state->root_skb could be replaced with
+ * a stack for this purpose.
+ */
+unsigned int skb_seq_read(unsigned int consumed, const u8 **data,
+ struct skb_seq_state *st)
+{
+ unsigned int block_limit, abs_offset = consumed + st->lower_offset;
+ skb_frag_t *frag;
+
+ if (unlikely(abs_offset >= st->upper_offset))
+ return 0;
+
+next_skb:
+ block_limit = skb_headlen(st->cur_skb);
+
+ if (abs_offset < block_limit) {
+ *data = st->cur_skb->data + abs_offset;
+ return block_limit - abs_offset;
+ }
+
+ if (st->frag_idx == 0 && !st->frag_data)
+ st->stepped_offset += skb_headlen(st->cur_skb);
+
+ while (st->frag_idx < skb_shinfo(st->cur_skb)->nr_frags) {
+ frag = &skb_shinfo(st->cur_skb)->frags[st->frag_idx];
+ block_limit = frag->size + st->stepped_offset;
+
+ if (abs_offset < block_limit) {
+ if (!st->frag_data)
+ st->frag_data = kmap_skb_frag(frag);
+
+ *data = (u8 *) st->frag_data + frag->page_offset +
+ (abs_offset - st->stepped_offset);
+
+ return block_limit - abs_offset;
+ }
+
+ if (st->frag_data) {
+ kunmap_skb_frag(st->frag_data);
+ st->frag_data = NULL;
+ }
+
+ st->frag_idx++;
+ st->stepped_offset += frag->size;
+ }
+
+ if (st->cur_skb->next) {
+ st->cur_skb = st->cur_skb->next;
+ st->frag_idx = 0;
+ goto next_skb;
+ } else if (st->root_skb == st->cur_skb &&
+ skb_shinfo(st->root_skb)->frag_list) {
+ st->cur_skb = skb_shinfo(st->root_skb)->frag_list;
+ goto next_skb;
+ }
+
+ return 0;
+}
+
+/**
+ * skb_abort_seq_read - Abort a sequential read of skb data
+ * @st: state variable
+ *
+ * Must be called if skb_seq_read() was not called until it
+ * returned 0.
+ */
+void skb_abort_seq_read(struct skb_seq_state *st)
+{
+ if (st->frag_data)
+ kunmap_skb_frag(st->frag_data);
+}
+
void __init skb_init(void)
{
skbuff_head_cache = kmem_cache_create("skbuff_head_cache",
@@ -1538,3 +1652,6 @@
EXPORT_SYMBOL(skb_unlink);
EXPORT_SYMBOL(skb_append);
EXPORT_SYMBOL(skb_split);
+EXPORT_SYMBOL(skb_prepare_seq_read);
+EXPORT_SYMBOL(skb_seq_read);
+EXPORT_SYMBOL(skb_abort_seq_read);