Hi,
On Tue, Jan 30, 2018 at 12:14:46PM +1100, Daniel Axtens wrote:
> If you take a GSO skb, and split it into packets, will the MAC
> length (L2 + L3 + L4 headers + payload) of those packets be small
> enough to fit within a given length?
>
> Move skb_gso_mac_seglen() to skbuff.h with other related functions
> like skb_gso_network_seglen() so we can use it, and then create
> skb_gso_validate_mac_len to do the full calculation.
>
> Signed-off-by: Daniel Axtens <d...@axtens.net>
> ---
> include/linux/skbuff.h | 16 +++++++++++++
> net/core/skbuff.c | 65
> +++++++++++++++++++++++++++++++++++++++-----------
> net/sched/sch_tbf.c | 10 --------
> 3 files changed, 67 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index b8e0da6c27d6..242d6773c7c2 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -3287,6 +3287,7 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb,
> int shiftlen);
> void skb_scrub_packet(struct sk_buff *skb, bool xnet);
> unsigned int skb_gso_transport_seglen(const struct sk_buff *skb);
> bool skb_gso_validate_mtu(const struct sk_buff *skb, unsigned int mtu);
> +bool skb_gso_validate_mac_len(const struct sk_buff *skb, unsigned int len);
> struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features);
> struct sk_buff *skb_vlan_untag(struct sk_buff *skb);
> int skb_ensure_writable(struct sk_buff *skb, int write_len);
> @@ -4120,6 +4121,21 @@ static inline unsigned int
> skb_gso_network_seglen(const struct sk_buff *skb)
> return hdr_len + skb_gso_transport_seglen(skb);
> }
>
> +/**
> + * skb_gso_mac_seglen - Return length of individual segments of a gso packet
> + *
> + * @skb: GSO skb
> + *
> + * skb_gso_mac_seglen is used to determine the real size of the
> + * individual segments, including MAC/L2, Layer3 (IP, IPv6) and L4
> + * headers (TCP/UDP).
> + */
> +static inline unsigned int skb_gso_mac_seglen(const struct sk_buff *skb)
> +{
> + unsigned int hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
> + return hdr_len + skb_gso_transport_seglen(skb);
> +}
> +
> /* Local Checksum Offload.
> * Compute outer checksum based on the assumption that the
> * inner checksum will be offloaded later.
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 01e8285aea73..55d84ab7d093 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4914,36 +4914,73 @@ unsigned int skb_gso_transport_seglen(const struct
> sk_buff *skb)
> EXPORT_SYMBOL_GPL(skb_gso_transport_seglen);
>
> /**
> - * skb_gso_validate_mtu - Return in case such skb fits a given MTU
> + * skb_gso_size_check - check the skb size, considering GSO_BY_FRAGS
> *
> - * @skb: GSO skb
> - * @mtu: MTU to validate against
> + * There are a couple of instances where we have a GSO skb, and we
> + * want to determine what size it would be after it is segmented.
> *
> - * skb_gso_validate_mtu validates if a given skb will fit a wanted MTU
> - * once split.
> + * We might want to check:
> + * - L3+L4+payload size (e.g. IP forwarding)
> + * - L2+L3+L4+payload size (e.g. sanity check before passing to driver)
> + *
> + * This is a helper to do that correctly considering GSO_BY_FRAGS.
> + *
> + * @seg_len: The segmented length (from skb_gso_*_seglen). In the
> + * GSO_BY_FRAGS case this will be [header sizes + GSO_BY_FRAGS].
> + *
> + * @max_len: The maximum permissible length.
> + *
> + * Returns true if the segmented length <= max length.
> */
> -bool skb_gso_validate_mtu(const struct sk_buff *skb, unsigned int mtu)
> -{
> +static inline bool skb_gso_size_check(const struct sk_buff *skb,
> + unsigned int seg_len,
> + unsigned int max_len) {
> const struct skb_shared_info *shinfo = skb_shinfo(skb);
> const struct sk_buff *iter;
> - unsigned int hlen;
> -
> - hlen = skb_gso_network_seglen(skb);
>
> if (shinfo->gso_size != GSO_BY_FRAGS)
> - return hlen <= mtu;
> + return seg_len <= max_len;
>
> /* Undo this so we can re-use header sizes */
> - hlen -= GSO_BY_FRAGS;
> + seg_len -= GSO_BY_FRAGS;
>
> skb_walk_frags(skb, iter) {
> - if (hlen + skb_headlen(iter) > mtu)
> + if (seg_len + skb_headlen(iter) > max_len)
> return false;
> }
>
> return true;
> }
> -EXPORT_SYMBOL_GPL(skb_gso_validate_mtu);
> +
> +/**
> + * skb_gso_validate_mtu - Return in case such skb fits a given MTU
> + *
> + * @skb: GSO skb
> + * @mtu: MTU to validate against
> + *
> + * skb_gso_validate_mtu validates if a given skb will fit a wanted MTU
> + * once split.
> + */
> +bool skb_gso_validate_mtu(const struct sk_buff *skb, unsigned int mtu)
> +{
> + return skb_gso_size_check(skb, skb_gso_network_seglen(skb), mtu);
> +}
> +EXPORT_SYMBOL_GPL(skb_gso_validate_network_len);
This export is not matching the function name.
