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Fan Yu ad892e912b tcp: trace retransmit failures in tcp_retransmit_skb 
Background
==========
When TCP retransmits a packet due to missing ACKs, the
retransmission may fail for various reasons (e.g., packets
stuck in driver queues, receiver zero windows, or routing issues).

The original tcp_retransmit_skb tracepoint:

  'commit e086101b15 ("tcp: add a tracepoint for tcp retransmission")'

lacks visibility into these failure causes, making production
diagnostics difficult.

Solution
========
Adds the retval("err") to the tcp_retransmit_skb tracepoint.
Enables users to know why some tcp retransmission failed and
users can filter retransmission failures by retval.

Compatibility description
=========================
This patch extends the tcp_retransmit_skb tracepoint
by adding a new "err" field at the end of its
existing structure (within TP_STRUCT__entry). The
compatibility implications are detailed as follows:

1) Structural compatibility for legacy user-space tools
Legacy tools/BPF programs accessing existing fields
(by offset or name) can still work without modification
or recompilation.The new field is appended to the end,
preserving original memory layout.

2) Note: semantic changes
The original tracepoint primarily only focused on
successfully retransmitted packets. With this patch,
the tracepoint now can figure out packets that may
terminate early due to specific reasons. For accurate
statistics, users should filter using "err" to
distinguish outcomes.

Before patched:
field:const void * skbaddr; offset:8; size:8; signed:0;
field:const void * skaddr; offset:16; size:8; signed:0;
field:int state; offset:24; size:4; signed:1;
field:__u16 sport; offset:28; size:2; signed:0;
field:__u16 dport; offset:30; size:2; signed:0;
field:__u16 family; offset:32; size:2; signed:0;
field:__u8 saddr[4]; offset:34; size:4; signed:0;
field:__u8 daddr[4]; offset:38; size:4; signed:0;
field:__u8 saddr_v6[16]; offset:42; size:16; signed:0;
field:__u8 daddr_v6[16]; offset:58; size:16; signed:0;

print fmt: "skbaddr=%p skaddr=%p family=%s sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c state=%s"

After patched:
field:const void * skbaddr; offset:8; size:8; signed:0;
field:const void * skaddr; offset:16; size:8; signed:0;
field:int state; offset:24; size:4; signed:1;
field:__u16 sport; offset:28; size:2; signed:0;
field:__u16 dport; offset:30; size:2; signed:0;
field:__u16 family; offset:32; size:2; signed:0;
field:__u8 saddr[4]; offset:34; size:4; signed:0;
field:__u8 daddr[4]; offset:38; size:4; signed:0;
field:__u8 saddr_v6[16]; offset:42; size:16; signed:0;
field:__u8 daddr_v6[16]; offset:58; size:16; signed:0;
field:int err; offset:76; size:4; signed:1;

print fmt: "skbaddr=%p skaddr=%p family=%s sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c state=%s err=%d"

Co-developed-by: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: Fan Yu <fan.yu9@zte.com.cn>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250721111607626_BDnIJB0ywk6FghN63bor@zte.com.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2025-07-22 18:19:11 -07:00
arch ibmveth: Add multi buffers rx replenishment hcall support 2025-07-22 15:08:23 +02:00
block block-6.16-20250626 2025-06-27 09:02:33 -07:00
certs
crypto crypto: wp512 - Use API partial block handling 2025-06-23 16:56:56 +08:00
Documentation ethtool: rss: support removing contexts via Netlink 2025-07-21 18:21:19 -07:00
drivers net: netdevsim: hook in XDP handling 2025-07-22 18:15:53 -07:00
fs net: s/dev_get_flags/netif_get_flags/ 2025-07-18 17:27:47 -07:00
include tcp: trace retransmit failures in tcp_retransmit_skb 2025-07-22 18:19:11 -07:00
init futex: Temporary disable FUTEX_PRIVATE_HASH 2025-07-01 15:02:05 +02:00
io_uring io_uring-6.16-20250710 2025-07-11 10:29:30 -07:00
ipc - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-07-17 11:00:33 -07:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-07-17 11:00:33 -07:00
LICENSES LICENSES: add CC0-1.0 license text 2025-05-21 14:54:17 +02:00
mm Revert "sched/numa: add statistics of numa balance task" 2025-07-09 21:07:56 -07:00
net tcp: trace retransmit failures in tcp_retransmit_skb 2025-07-22 18:19:11 -07:00
rust Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-07-17 11:00:33 -07:00
samples samples/damon: fix damon sample mtier for start failure 2025-07-09 21:07:55 -07:00
scripts Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-07-17 11:00:33 -07:00
security selinux: change security_compute_sid to return the ssid or tsid on match 2025-06-19 16:13:16 -04:00
sound ALSA: hda/realtek: Enable headset Mic on Positivo K116J 2025-07-07 14:09:09 +02:00
tools selftests: drv-net: Test head-adjustment support 2025-07-22 18:15:53 -07:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt KVM: Allow CPU to reschedule while setting per-page memory attributes 2025-06-24 12:20:17 -07:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig
.editorconfig
.get_maintainer.ignore
.gitattributes
.gitignore .gitignore: ignore Python compiled bytecode 2025-04-24 10:12:46 -06:00
.mailmap MAINTAINERS: Update Kirill Shutemov's email address for TDX 2025-07-11 07:25:51 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.rustfmt.toml
COPYING
CREDITS CREDITS: Add entry for Shannon Nelson 2025-06-21 07:34:28 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-07-17 11:00:33 -07:00
Makefile Linux 6.16-rc6 2025-07-13 14:25:58 -07:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.