[PATCH net v2 1/3] xsk: align TX metadata layout across ABIs

[Stanislav Fomichev <sdf.kernel@gmail.com>]

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

On i386 and m68k, 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 while the interface is still new.

Fixes: ca4419f15abd ("xsk: Add launch time hardware offload support to XDP Tx metadata")
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
---
 include/uapi/linux/if_xdp.h       | 1 +
 tools/include/uapi/linux/if_xdp.h | 1 +
 2 files changed, 2 insertions(+)

diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
index 23a062781468..50d67df78911 100644
--- a/include/uapi/linux/if_xdp.h
+++ b/include/uapi/linux/if_xdp.h
@@ -149,6 +149,7 @@ struct xsk_tx_metadata {
 			__u16 csum_start;
 			/* Offset from csum_start where checksum should be stored. */
 			__u16 csum_offset;
+			__u32 reserved;
 
 			/* XDP_TXMD_FLAGS_LAUNCH_TIME */
 			/* Launch time in nanosecond against the PTP HW Clock */
diff --git a/tools/include/uapi/linux/if_xdp.h b/tools/include/uapi/linux/if_xdp.h
index 23a062781468..50d67df78911 100644
--- a/tools/include/uapi/linux/if_xdp.h
+++ b/tools/include/uapi/linux/if_xdp.h
@@ -149,6 +149,7 @@ struct xsk_tx_metadata {
 			__u16 csum_start;
 			/* Offset from csum_start where checksum should be stored. */
 			__u16 csum_offset;
+			__u32 reserved;
 
 			/* XDP_TXMD_FLAGS_LAUNCH_TIME */
 			/* Launch time in nanosecond against the PTP HW Clock */
-- 
2.53.0-Meta