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[PATCH 1/6] macvtap: zerocopy: fix offset calculation when building skb

April 16th, 2012 - 02:20 am ET by Jason Wang | Report spam
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This patch fixes the offset calculation when build skb:

- offset1 were used as skb data offset not vector offset
- reset offset to zero only when we advance to next vector

Signed-off-by: Jason Wang <jasowang@redhat.com>

drivers/net/macvtap.c | 13 +++++++
1 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 0427c65..bd4a70d 100644
a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -505,10 +505,11 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
if (copy > size) {
++from;
- }
+ offset = 0;
+ } else
+ offset += size;
copy -= size;
offset1 += size;
- offset = 0;
}

if (len == offset1)
@@ -519,13 +520,13 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
int num_pages;
unsigned long base;

- len = from->iov_len - offset1;
+ len = from->iov_len - offset;
if (!len) {
- offset1 = 0;
+ offset = 0;
++from;
continue;
}
- base = (unsigned long)from->iov_base + offset1;
+ base = (unsigned long)from->iov_base + offset;
size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
num_pages = get_user_pages_fast(base, size, 0, &page[i]);
if ((num_pages != size) ||
@@ -546,7 +547,7 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
len -= size;
i++;
}
- offset1 = 0;
+ offset = 0;
++from;
}
return 0;

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#1 Jason Wang
April 16th, 2012 - 02:20 am ET | Report spam
As the skb fragment were pinned/built from user pages, we should
account the page instead of length for truesize.

Signed-off-by: Jason Wang

drivers/net/macvtap.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index bd4a70d..7cb2684 100644
a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -519,6 +519,7 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
struct page *page[MAX_SKB_FRAGS];
int num_pages;
unsigned long base;
+ unsigned long truesize;

len = from->iov_len - offset;
if (!len) {
@@ -533,10 +534,11 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
(num_pages > MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags))
/* put_page is in skb free */
return -EFAULT;
+ truesize = size * PAGE_SIZE;
skb->data_len += len;
skb->len += len;
- skb->truesize += len;
- atomic_add(len, &skb->sk->sk_wmem_alloc);
+ skb->truesize += truesize;
+ atomic_add(truesize, &skb->sk->sk_wmem_alloc);
while (len) {
int off = base & ~PAGE_MASK;
int size = min_t(int, len, PAGE_SIZE - off);

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