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Diffstat (limited to 'Documentation/networking/segmentation-offloads.txt')
| -rw-r--r-- | Documentation/networking/segmentation-offloads.txt | 46 |
1 files changed, 30 insertions, 16 deletions
diff --git a/Documentation/networking/segmentation-offloads.txt b/Documentation/networking/segmentation-offloads.txt index aca542ec125c..1794bfe98196 100644 --- a/Documentation/networking/segmentation-offloads.txt +++ b/Documentation/networking/segmentation-offloads.txt @@ -1,4 +1,9 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=================================================== Segmentation Offloads in the Linux Networking Stack +=================================================== + Introduction ============ @@ -15,6 +20,7 @@ The following technologies are described: * Partial Generic Segmentation Offload - GSO_PARTIAL * SCTP accelleration with GSO - GSO_BY_FRAGS + TCP Segmentation Offload ======================== @@ -42,6 +48,7 @@ NETIF_F_TSO_MANGLEID set then the IP ID can be ignored when performing TSO and we will either increment the IP ID for all frames, or leave it at a static value based on driver preference. + UDP Fragmentation Offload ========================= @@ -54,6 +61,7 @@ UFO is deprecated: modern kernels will no longer generate UFO skbs, but can still receive them from tuntap and similar devices. Offload of UDP-based tunnel protocols is still supported. + IPIP, SIT, GRE, UDP Tunnel, and Remote Checksum Offloads ======================================================== @@ -71,17 +79,19 @@ refer to the tunnel headers as the outer headers, while the encapsulated data is normally referred to as the inner headers. Below is the list of calls to access the given headers: -IPIP/SIT Tunnel: - Outer Inner -MAC skb_mac_header -Network skb_network_header skb_inner_network_header -Transport skb_transport_header +IPIP/SIT Tunnel:: + + Outer Inner + MAC skb_mac_header + Network skb_network_header skb_inner_network_header + Transport skb_transport_header -UDP/GRE Tunnel: - Outer Inner -MAC skb_mac_header skb_inner_mac_header -Network skb_network_header skb_inner_network_header -Transport skb_transport_header skb_inner_transport_header +UDP/GRE Tunnel:: + + Outer Inner + MAC skb_mac_header skb_inner_mac_header + Network skb_network_header skb_inner_network_header + Transport skb_transport_header skb_inner_transport_header In addition to the above tunnel types there are also SKB_GSO_GRE_CSUM and SKB_GSO_UDP_TUNNEL_CSUM. These two additional tunnel types reflect the @@ -93,6 +103,7 @@ header has requested a remote checksum offload. In this case the inner headers will be left with a partial checksum and only the outer header checksum will be computed. + Generic Segmentation Offload ============================ @@ -106,6 +117,7 @@ Before enabling any hardware segmentation offload a corresponding software offload is required in GSO. Otherwise it becomes possible for a frame to be re-routed between devices and end up being unable to be transmitted. + Generic Receive Offload ======================= @@ -117,6 +129,7 @@ this is IPv4 ID in the case that the DF bit is set for a given IP header. If the value of the IPv4 ID is not sequentially incrementing it will be altered so that it is when a frame assembled via GRO is segmented via GSO. + Partial Generic Segmentation Offload ==================================== @@ -134,6 +147,7 @@ is the outer IPv4 ID field. It is up to the device drivers to guarantee that the IPv4 ID field is incremented in the case that a given header does not have the DF bit set. + SCTP accelleration with GSO =========================== @@ -157,14 +171,14 @@ appropriately. There are some helpers to make this easier: - - skb_is_gso(skb) && skb_is_gso_sctp(skb) is the best way to see if - an skb is an SCTP GSO skb. +- skb_is_gso(skb) && skb_is_gso_sctp(skb) is the best way to see if + an skb is an SCTP GSO skb. - - For size checks, the skb_gso_validate_*_len family of helpers correctly - considers GSO_BY_FRAGS. +- For size checks, the skb_gso_validate_*_len family of helpers correctly + considers GSO_BY_FRAGS. - - For manipulating packets, skb_increase_gso_size and skb_decrease_gso_size - will check for GSO_BY_FRAGS and WARN if asked to manipulate these skbs. +- For manipulating packets, skb_increase_gso_size and skb_decrease_gso_size + will check for GSO_BY_FRAGS and WARN if asked to manipulate these skbs. This also affects drivers with the NETIF_F_FRAGLIST & NETIF_F_GSO_SCTP bits set. Note also that NETIF_F_GSO_SCTP is included in NETIF_F_GSO_SOFTWARE. |