# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID e3af1912794bcd4d6266e969fba3029e8d3a20ab
# Parent aecdb4c52fa78dc2824f6be011689a2c4de4de11
[NET] back: Add a few comments to the goriest parts of the scatter-gather patch.
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
---
linux-2.6-xen-sparse/drivers/xen/netback/netback.c | 47 ++++++++++-----------
1 files changed, 23 insertions(+), 24 deletions(-)
diff -r aecdb4c52fa7 -r e3af1912794b
linux-2.6-xen-sparse/drivers/xen/netback/netback.c
--- a/linux-2.6-xen-sparse/drivers/xen/netback/netback.c Mon Jun 05
16:33:49 2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/netback/netback.c Mon Jun 05
17:03:19 2006 +0100
@@ -543,17 +543,14 @@ static gnttab_map_grant_ref_t *netbk_get
skb_frag_t *frags = shinfo->frags;
netif_tx_request_t *txp;
unsigned long pending_idx = *((u16 *)skb->data);
- int nr_frags = shinfo->nr_frags;
RING_IDX cons = netif->tx.req_cons + 1;
- int i;
-
- if ((unsigned long)shinfo->frags[0].page == pending_idx) {
- frags++;
- nr_frags--;
- }
-
- for (i = 0; i < nr_frags; i++) {
- txp = RING_GET_REQUEST(&netif->tx, cons + i);
+ int i, start;
+
+ /* Skip first skb fragment if it is on same page as header fragment. */
+ start = ((unsigned long)shinfo->frags[0].page == pending_idx);
+
+ for (i = start; i < shinfo->nr_frags; i++) {
+ txp = RING_GET_REQUEST(&netif->tx, cons++);
pending_idx = pending_ring[MASK_PEND_IDX(pending_cons++)];
gnttab_set_map_op(mop++, MMAP_VADDR(pending_idx),
@@ -578,10 +575,9 @@ static int netbk_tx_check_mop(struct sk_
netif_tx_request_t *txp;
struct skb_shared_info *shinfo = skb_shinfo(skb);
int nr_frags = shinfo->nr_frags;
- int start;
- int err;
- int i;
-
+ int i, err, start;
+
+ /* Check status of header. */
err = mop->status;
if (unlikely(err)) {
txp = &pending_tx_info[pending_idx].req;
@@ -595,44 +591,47 @@ static int netbk_tx_check_mop(struct sk_
grant_tx_handle[pending_idx] = mop->handle;
}
- start = 0;
- if ((unsigned long)shinfo->frags[0].page == pending_idx)
- start++;
+ /* Skip first skb fragment if it is on same page as header fragment. */
+ start = ((unsigned long)shinfo->frags[0].page == pending_idx);
for (i = start; i < nr_frags; i++) {
- int newerr;
- int j;
+ int j, newerr;
pending_idx = (unsigned long)shinfo->frags[i].page;
+ /* Check error status: if okay then remember grant handle. */
newerr = (++mop)->status;
if (likely(!newerr)) {
set_phys_to_machine(
- __pa(MMAP_VADDR(pending_idx)) >> PAGE_SHIFT,
- FOREIGN_FRAME(mop->dev_bus_addr >> PAGE_SHIFT));
+ __pa(MMAP_VADDR(pending_idx))>>PAGE_SHIFT,
+ FOREIGN_FRAME(mop->dev_bus_addr>>PAGE_SHIFT));
grant_tx_handle[pending_idx] = mop->handle;
-
+ /* Had a previous error? Invalidate this fragment. */
if (unlikely(err))
netif_idx_release(pending_idx);
continue;
}
+ /* Error on this fragment: respond to client with an error. */
txp = &pending_tx_info[pending_idx].req;
make_tx_response(netif, txp->id, NETIF_RSP_ERROR);
pending_ring[MASK_PEND_IDX(pending_prod++)] = pending_idx;
netif_put(netif);
+ /* Not the first error? Preceding frags already invalidated. */
if (err)
continue;
+ /* First error: invalidate header and preceding fragments. */
pending_idx = *((u16 *)skb->data);
netif_idx_release(pending_idx);
-
for (j = start; j < i; j++) {
pending_idx = (unsigned long)shinfo->frags[i].page;
netif_idx_release(pending_idx);
}
- err |= newerr;
+
+ /* Remember the error: invalidate all subsequent fragments. */
+ err = newerr;
}
*mopp = mop + 1;
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