passt/tcp_internal.h, branch 2026_05_26.038c51e

tcp: Encode checksum computation flags in a single parameter

2026-05-26T10:17:10+00:00

tcp_fill_headers() takes a pointer to a previously computed IPv4 header
checksum to avoid recalculating it when the payload length doesn't
change, and a separate bool to skip TCP checksum computation.

Replace both parameters with a single uint32_t csum_flags that encodes:
- IP4_CSUM (bit 31): compute IPv4 header checksum from scratch
- TCP_CSUM (bit 30): compute TCP checksum
- IP4_CMASK (low 16 bits): cached IPv4 header checksum value

When IP4_CSUM is not set, the cached checksum is extracted from the low
16 bits.  This is cleaner than the pointer-based approach, and also
avoids a potential dangling pointer issue: a subsequent patch makes
tcp_fill_headers() access ip4h via with_header(), which scopes it to a
temporary variable, so a pointer to ip4h->check would become invalid
after the with_header() block.

Suggested-by: David Gibson 
Signed-off-by: Laurent Vivier 
Reviewed-by: Jon Maloy 
Reviewed-by: David Gibson 
Signed-off-by: Stefano Brivio

tcp: Pass explicit data length to tcp_fill_headers()

2026-05-19T23:21:51+00:00

tcp_fill_headers() computed the TCP payload length from iov_tail_size(),
but with vhost-user multibuffer frames, the iov_tail will be larger than
the actual data.  Pass the data length explicitly so that IP total
length, pseudo-header, and checksum computations use the correct value.

Signed-off-by: Laurent Vivier 
Reviewed-by: David Gibson 
Reviewed-by: Jon Maloy 
Signed-off-by: Stefano Brivio

Add missing includes to headers

2026-03-04T16:39:57+00:00

Support build systems like bazel that check that headers are
self-contained.

Also update includes so that clang-include-cleaner succeeds.

Tested with:
clang-include-cleaner-19 --extra-arg=-D_GNU_SOURCE --extra-arg=-DPAGE_SIZE=4096 --extra-arg=-DVERSION=\"git\" --extra-arg=-DHAS_GETRANDOM *.h *.c

Signed-off-by: Peter Foley 
Signed-off-by: Stefano Brivio

tcp: Extend tcp_send_flag() to send TCP keepalive segments

2026-02-24T23:17:41+00:00

TCP keepalives aren't technically a flag, but they are a zero-data segment
so they can be generated with only a small modification to
tcp_{buf,vu}_send_flag().  Implement this, using a new "pseudo-flag"
value (similar to DUP_ACK), KEEPALIVE.

Signed-off-by: David Gibson 
[sbrivio: Fix trivial merge conflict with 812cdb802c6e]
Signed-off-by: Stefano Brivio

tcp: Move tap header update out of tcp_fill_headers()

2026-02-15T01:52:42+00:00

tcp_fill_headers() currently calls tap_hdr_update() to set the frame
length in the tap-specific header.  This is backend-specific: the tap
backend needs this for its frame length header, but the vhost-user
backend passes NULL for the tap header and doesn't use it at all.

Remove the tap_hdr parameter from tcp_fill_headers() and instead return
the computed L2 frame length.  The tap backend caller,
tcp_l2_buf_fill_headers(), now calls tap_hdr_update() itself with the
returned length.  The vhost-user callers, tcp_vu_send_flag() and
tcp_vu_prepare(), no longer need to pass a NULL tap header.

Signed-off-by: Laurent Vivier 
Signed-off-by: Stefano Brivio

tcp, udp: Pad batched frames to 60 bytes (802.3 minimum) in non-vhost-user modes

2025-12-08T03:47:22+00:00

Add a further iovec frame part, TCP_IOV_ETH_PAD for TCP and
UDP_IOV_ETH_PAD for UDP, after the payload, make that point to a
zero-filled buffer, and send out a part of it if needed to reach
the minimum frame length given by 802.3, that is, 60 bytes altogether.

The frames we might need to pad are IPv4 only (the IPv6 header is
larger), and are typically TCP ACK segments but can also be small
data segments or datagrams.

Link: https://bugs.passt.top/show_bug.cgi?id=166
Signed-off-by: Stefano Brivio 
Reviewed-by: David Gibson

tcp: Fix coding style for comment to enum tcp_iov_parts

2025-12-08T03:47:16+00:00

...as I'm going to add a new value to it.

Fixes: 95601237ef82 ("tcp: Replace TCP buffer structure by an iovec array")
Signed-off-by: Stefano Brivio 
Reviewed-by: David Gibson 
Reviewed-by: Laurent Vivier

tcp: forward external source MAC address through tap interface

2025-10-30T11:01:01+00:00

We forward the incoming mac address through the tap interface when
receiving incoming packets from network local hosts.

This is a part of the solution to bug
https://bugs.passt.top/show_bug.cgi?id=120

Signed-off-by: Jon Maloy 
Reviewed-by: David Gibson 
Signed-off-by: Stefano Brivio

Reduce tcp_buf_discard size

2025-09-11T15:09:03+00:00

On kernels without SO_PEEK_OFF, a 16MB static buffer is used to
discard sent data. This patch reduces the buffer to 1MB.

Larger discards are now handled by using multiple iovec entries
pointing to the same 1MB buffer.

Signed-off-by: Xun Gu 
[sbrivio: Drop stray whitespace after BUF_DISCARD_SIZE define]
Signed-off-by: Stefano Brivio

tcp: Cast operands of sequence comparison macros to uint32_t before using them

2025-09-11T15:03:45+00:00

Otherwise, passing signed types causes automatic promotion of the
result of the subtractions as well, which is not what we want, as
these macros rely on unsigned 32-bit arithmetic.

The next patch introduces a ssize_t operand for SEQ_LE, illustrating
the issue.

Signed-off-by: Stefano Brivio 
Reviewed-by: David Gibson 
Tested-by: Paul Holzinger 
Reviewed-by: Jon Maloy