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    SubjectRe: [RFC PATCH v3 09/12] net: add support for skbs with unreadable frags
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    On 11/5/23 7:44 PM, Mina Almasry wrote:
    > diff --git a/net/core/datagram.c b/net/core/datagram.c
    > index 176eb5834746..cdd4fb129968 100644
    > --- a/net/core/datagram.c
    > +++ b/net/core/datagram.c
    > @@ -425,6 +425,9 @@ static int __skb_datagram_iter(const struct sk_buff *skb, int offset,
    > return 0;
    > }
    >
    > + if (skb_frags_not_readable(skb))
    > + goto short_copy;
    > +
    > /* Copy paged appendix. Hmm... why does this look so complicated? */
    > for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
    > int end;
    > @@ -616,6 +619,9 @@ int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk,
    > {
    > int frag;
    >
    > + if (skb_frags_not_readable(skb))
    > + return -EFAULT;

    This check ....
    > +
    > if (msg && msg->msg_ubuf && msg->sg_from_iter)
    > return msg->sg_from_iter(sk, skb, from, length);


    ... should go here. That allows custome sg_from_iter to have access to
    the skb. What matters is not expecting struct page (e.g., refcounting);
    if the custom iter does not do that then all is well. io_uring's iter
    does not look at the pages, so all good.

    >
    > diff --git a/net/core/gro.c b/net/core/gro.c
    > index 42d7f6755f32..56046d65386a 100644
    > --- a/net/core/gro.c
    > +++ b/net/core/gro.c
    > @@ -390,6 +390,9 @@ static void gro_pull_from_frag0(struct sk_buff *skb, int grow)
    > {
    > struct skb_shared_info *pinfo = skb_shinfo(skb);
    >
    > + if (WARN_ON_ONCE(skb_frags_not_readable(skb)))
    > + return;
    > +
    > BUG_ON(skb->end - skb->tail < grow);
    >
    > memcpy(skb_tail_pointer(skb), NAPI_GRO_CB(skb)->frag0, grow);
    > @@ -411,7 +414,7 @@ static void gro_try_pull_from_frag0(struct sk_buff *skb)
    > {
    > int grow = skb_gro_offset(skb) - skb_headlen(skb);
    >
    > - if (grow > 0)
    > + if (grow > 0 && !skb_frags_not_readable(skb))
    > gro_pull_from_frag0(skb, grow);
    > }
    >
    > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
    > index 13eca4fd25e1..f01673ed2eff 100644
    > --- a/net/core/skbuff.c
    > +++ b/net/core/skbuff.c
    > @@ -1230,6 +1230,14 @@ void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt)
    > struct page *p;
    > u8 *vaddr;
    >
    > + if (skb_frag_is_page_pool_iov(frag)) {

    Why skb_frag_is_page_pool_iov here vs skb_frags_not_readable?

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