linux.git/tools/include/uapi/linux/if_xdp.h, branch v7.3-rc2

xsk: align TX metadata layout across ABIs

2026-08-24T18:11:59+00:00

Add explicit padding before launch_time so xsk_tx_metadata has the same
layout on 32-bit and 64-bit systems.

On several architectures (csky, i386, nios2, m65k, openrisc, sh), the old
native 32-bit layout put launch_time at offset 12 and had a natural size of
20 bytes. Using sizeof(struct xsk_tx_metadata) as tx_metadata_len was already
rejected because the length must be a multiple of eight, so the
straightforward use of the interface was broken on those ABIs. Userspace
could still register a padded length of 24 bytes, though; mixing the old and
new layouts then silently reads launch_time from the wrong offset and
misprograms packet launch times. This intentionally replaces that
incompatible layout because the affected architectures are unlikely to
have any notable users. (x86_64 and arm64 have the most users and are _not_
affected)

Fixes: ca4419f15abd ("xsk: Add launch time hardware offload support to XDP Tx metadata")
Reviewed-by: Simon Horman 
Signed-off-by: Stanislav Fomichev 
Link: https://patch.msgid.link/20260819160535.1472459-2-sdf@fomichev.me
Signed-off-by: Jakub Kicinski

net: xsk: introduce XDP_MAX_TX_SKB_BUDGET setsockopt

2025-07-10T12:48:29+00:00

This patch provides a setsockopt method to let applications leverage to
adjust how many descs to be handled at most in one send syscall. It
mitigates the situation where the default value (32) that is too small
leads to higher frequency of triggering send syscall.

Considering the prosperity/complexity the applications have, there is no
absolutely ideal suggestion fitting all cases. So keep 32 as its default
value like before.

The patch does the following things:
- Add XDP_MAX_TX_SKB_BUDGET socket option.
- Set max_tx_budget to 32 by default in the initialization phase as a
  per-socket granular control.
- Set the range of max_tx_budget as [32, xs->tx->nentries].

The idea behind this comes out of real workloads in production. We use a
user-level stack with xsk support to accelerate sending packets and
minimize triggering syscalls. When the packets are aggregated, it's not
hard to hit the upper bound (namely, 32). The moment user-space stack
fetches the -EAGAIN error number passed from sendto(), it will loop to try
again until all the expected descs from tx ring are sent out to the driver.
Enlarging the XDP_MAX_TX_SKB_BUDGET value contributes to less frequency of
sendto() and higher throughput/PPS.

Here is what I did in production, along with some numbers as follows:
For one application I saw lately, I suggested using 128 as max_tx_budget
because I saw two limitations without changing any default configuration:
1) XDP_MAX_TX_SKB_BUDGET, 2) socket sndbuf which is 212992 decided by
net.core.wmem_default. As to XDP_MAX_TX_SKB_BUDGET, the scenario behind
this was I counted how many descs are transmitted to the driver at one
time of sendto() based on [1] patch and then I calculated the
possibility of hitting the upper bound. Finally I chose 128 as a
suitable value because 1) it covers most of the cases, 2) a higher
number would not bring evident results. After twisting the parameters,
a stable improvement of around 4% for both PPS and throughput and less
resources consumption were found to be observed by strace -c -p xxx:
1) %time was decreased by 7.8%
2) error counter was decreased from 18367 to 572

[1]: https://lore.kernel.org/all/20250619093641.70700-1-kerneljasonxing@gmail.com/

Signed-off-by: Jason Xing 
Acked-by: Maciej Fijalkowski 
Link: https://patch.msgid.link/20250704160138.48677-1-kerneljasonxing@gmail.com
Signed-off-by: Paolo Abeni

selftests/bpf: Fix bpf selftest build warning

2025-05-28T08:00:14+00:00

On linux-next, build for bpf selftest displays a warning:

Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h'
differs from latest version at 'include/uapi/linux/if_xdp.h'.

Commit 8066e388be48 ("net: add UAPI to the header guard in various network headers")
changed the header guard from _LINUX_IF_XDP_H to _UAPI_LINUX_IF_XDP_H
in include/uapi/linux/if_xdp.h.

To resolve the warning, update tools/include/uapi/linux/if_xdp.h
to align with the changes in include/uapi/linux/if_xdp.h

Fixes: 8066e388be48 ("net: add UAPI to the header guard in various network headers")
Reported-by: Venkat Rao Bagalkote 
Closes: https://lore.kernel.org/all/c2bc466d-dff2-4d0d-a797-9af7f676c065@linux.ibm.com/
Tested-by: Venkat Rao Bagalkote 
Signed-off-by: Saket Kumar Bhaskar 
Acked-by: Daniel Borkmann 
Link: https://patch.msgid.link/20250527054138.1086006-1-skb99@linux.ibm.com
Signed-off-by: Paolo Abeni

xsk: Add launch time hardware offload support to XDP Tx metadata

2025-02-20T23:13:45+00:00

Extend the XDP Tx metadata framework so that user can requests launch time
hardware offload, where the Ethernet device will schedule the packet for
transmission at a pre-determined time called launch time. The value of
launch time is communicated from user space to Ethernet driver via
launch_time field of struct xsk_tx_metadata.

Suggested-by: Stanislav Fomichev 
Signed-off-by: Song Yoong Siang 
Signed-off-by: Martin KaFai Lau 
Acked-by: Stanislav Fomichev 
Acked-by: Jakub Kicinski 
Link: https://patch.msgid.link/20250216093430.957880-2-yoong.siang.song@intel.com

tools: Sync if_xdp.h uapi tooling header

2025-01-17T14:49:16+00:00

Sync if_xdp.h uapi header to remove following warning:

  Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h'
  differs from latest version at 'include/uapi/linux/if_xdp.h'

Fixes: 48eb03dd2630 ("xsk: Add TX timestamp and TX checksum offload support")
Signed-off-by: Vishal Chourasia 
Signed-off-by: Song Yoong Siang 
Signed-off-by: Daniel Borkmann 
Link: https://lore.kernel.org/bpf/20250115032248.125742-1-yoong.siang.song@intel.com

selftests/bpf: Add XDP_UMEM_TX_METADATA_LEN to XSK TX metadata test

2024-07-25T09:57:33+00:00

This flag is now required to use tx_metadata_len.

Fixes: 40808a237d9c ("selftests/bpf: Add TX side to xdp_metadata")
Reported-by: Julian Schindel 
Signed-off-by: Stanislav Fomichev 
Signed-off-by: Daniel Borkmann 
Reviewed-by: Maciej Fijalkowski 
Link: https://lore.kernel.org/bpf/20240713015253.121248-3-sdf@fomichev.me

xsk: Add option to calculate TX checksum in SW

2023-11-29T22:59:40+00:00

For XDP_COPY mode, add a UMEM option XDP_UMEM_TX_SW_CSUM
to call skb_checksum_help in transmit path. Might be useful
to debugging issues with real hardware. I also use this mode
in the selftests.

Signed-off-by: Stanislav Fomichev 
Link: https://lore.kernel.org/r/20231127190319.1190813-9-sdf@google.com
Signed-off-by: Alexei Starovoitov

xsk: Add TX timestamp and TX checksum offload support

2023-11-29T22:59:40+00:00

This change actually defines the (initial) metadata layout
that should be used by AF_XDP userspace (xsk_tx_metadata).
The first field is flags which requests appropriate offloads,
followed by the offload-specific fields. The supported per-device
offloads are exported via netlink (new xsk-flags).

The offloads themselves are still implemented in a bit of a
framework-y fashion that's left from my initial kfunc attempt.
I'm introducing new xsk_tx_metadata_ops which drivers are
supposed to implement. The drivers are also supposed
to call xsk_tx_metadata_request/xsk_tx_metadata_complete in
the right places. Since xsk_tx_metadata_{request,_complete}
are static inline, we don't incur any extra overhead doing
indirect calls.

The benefit of this scheme is as follows:
- keeps all metadata layout parsing away from driver code
- makes it easy to grep and see which drivers implement what
- don't need any extra flags to maintain to keep track of what
  offloads are implemented; if the callback is implemented - the offload
  is supported (used by netlink reporting code)

Two offloads are defined right now:
1. XDP_TXMD_FLAGS_CHECKSUM: skb-style csum_start+csum_offset
2. XDP_TXMD_FLAGS_TIMESTAMP: writes TX timestamp back into metadata
   area upon completion (tx_timestamp field)

XDP_TXMD_FLAGS_TIMESTAMP is also implemented for XDP_COPY mode: it writes
SW timestamp from the skb destructor (note I'm reusing hwtstamps to pass
metadata pointer).

The struct is forward-compatible and can be extended in the future
by appending more fields.

Reviewed-by: Song Yoong Siang 
Signed-off-by: Stanislav Fomichev 
Acked-by: Jakub Kicinski 
Link: https://lore.kernel.org/r/20231127190319.1190813-3-sdf@google.com
Signed-off-by: Alexei Starovoitov

xsk: Support tx_metadata_len

2023-11-29T22:59:40+00:00

For zerocopy mode, tx_desc->addr can point to an arbitrary offset
and carry some TX metadata in the headroom. For copy mode, there
is no way currently to populate skb metadata.

Introduce new tx_metadata_len umem config option that indicates how many
bytes to treat as metadata. Metadata bytes come prior to tx_desc address
(same as in RX case).

The size of the metadata has mostly the same constraints as XDP:
- less than 256 bytes
- 8-byte aligned (compared to 4-byte alignment on xdp, due to 8-byte
  timestamp in the completion)
- non-zero

This data is not interpreted in any way right now.

Reviewed-by: Song Yoong Siang 
Signed-off-by: Stanislav Fomichev 
Reviewed-by: Jakub Kicinski 
Link: https://lore.kernel.org/r/20231127190319.1190813-2-sdf@google.com
Signed-off-by: Alexei Starovoitov

selftests/xsk: add basic multi-buffer test

2023-07-19T16:56:50+00:00

Add the first basic multi-buffer test that sends a stream of 9K
packets and validates that they are received at the other end. In
order to enable sending and receiving multi-buffer packets, code that
sets the MTU is introduced as well as modifications to the XDP
programs so that they signal that they are multi-buffer enabled.

Signed-off-by: Magnus Karlsson 
Link: https://lore.kernel.org/r/20230719132421.584801-20-maciej.fijalkowski@intel.com
Signed-off-by: Alexei Starovoitov