[PATCH net v5 0/2] packet: use consistent hard_header_len in send paths

AF_PACKET send paths read dev->hard_header_len at several stages of skb
allocation and construction. Concurrent netdevice reconfiguration can
make those reads inconsistent and cause skb headroom underflow.

Split the regular and TX_RING paths so each patch has one Fixes tag.
The separate SOCK_DGRAM consistency issue between hard_header_len and
header_ops->create remains outside this series.

Changes in v5:
- Drop the unnecessary per-frame copylen reset from patch 2.

Changes in v4:
- Use one hard_header_len snapshot throughout tpacket_snd(), including
  reserve and per-frame skb construction.
- Carry Willem's Reviewed-by on patch 1.

Link to v4: https://lore.kernel.org/netdev/20260729030122.21462-1-q.h.hack.winter@gmail.com/ (local)
Link to v3: https://lore.kernel.org/netdev/20260728031345.49562-1-q.h.hack.winter@gmail.com/ (local)

Qihang (2):
  packet: use consistent hard_header_len in non-ring send paths
  packet: use consistent hard_header_len in TX_RING send path

 include/linux/netdevice.h |  6 ++++--
 net/packet/af_packet.c    | 45 +++++++++++++++++++++++----------------
 2 files changed, 31 insertions(+), 20 deletions(-)

-- 
2.50.1 (Apple Git-155)