From: Jason Xing <kernelx...@tencent.com>

Add a new standalone file for the easy future extension to support
both active reset and passive reset in the TCP/DCCP/MPTCP protocols.

This patch only does the preparations for reset reason mechanism,
nothing else changes.

The reset reasons are divided into three parts:
1) reuse drop reasons for passive reset in TCP
2) reuse MP_TCPRST option for MPTCP
3) our own reasons

I will implement the basic codes of active/passive reset reason in
those three protocols, which is not complete for this moment. But
it provides a new chance to let other people add more reasons into
it:)

Signed-off-by: Jason Xing <kernelx...@tencent.com>
---
 include/net/rstreason.h | 93 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 include/net/rstreason.h

diff --git a/include/net/rstreason.h b/include/net/rstreason.h
new file mode 100644
index 000000000000..24d098a78a60
--- /dev/null
+++ b/include/net/rstreason.h
@@ -0,0 +1,93 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _LINUX_RSTREASON_H
+#define _LINUX_RSTREASON_H
+#include <net/dropreason-core.h>
+
+#define DEFINE_RST_REASON(FN, FNe)     \
+       FN(MPTCP_RST_EUNSPEC)           \
+       FN(MPTCP_RST_EMPTCP)            \
+       FN(MPTCP_RST_ERESOURCE)         \
+       FN(MPTCP_RST_EPROHIBIT)         \
+       FN(MPTCP_RST_EWQ2BIG)           \
+       FN(MPTCP_RST_EBADPERF)          \
+       FN(MPTCP_RST_EMIDDLEBOX)        \
+       FN(NOT_SPECIFIED)               \
+       FNe(MAX)
+
+#define RST_REASON_START (SKB_DROP_REASON_MAX + 1)
+
+/* There are three parts in order:
+ * 1) 0 - SKB_DROP_REASON_MAX: rely on drop reasons for passive reset in TCP
+ * 2) SKB_DROP_REASON_MAX + 1 - MPTCP_RST_EMIDDLEBOX: for MPTCP use
+ * 3) MPTCP_RST_EMIDDLEBOX - SK_RST_REASON_MAX: independent reset reason
+ */
+enum sk_rst_reason {
+       /* Leave this 'blank' part (0-SKB_DROP_REASON_MAX) for the reuse
+        * of skb drop reason because rst reason relies on what drop reason
+        * indicates exactly why it could happen.
+        */
+
+       /* Copy from include/uapi/linux/mptcp.h.
+        * These reset fields will not be changed since they adhere to
+        * RFC 8684. So do not touch them. I'm going to list each definition
+        * of them respectively.
+        */
+       /* Unspecified error.
+        * This is the default error; it implies that the subflow is no
+        * longer available. The presence of this option shows that the
+        * RST was generated by an MPTCP-aware device.
+        */
+       SK_RST_REASON_MPTCP_RST_EUNSPEC = RST_REASON_START,
+       /* MPTCP-specific error.
+        * An error has been detected in the processing of MPTCP options.
+        * This is the usual reason code to return in the cases where a RST
+        * is being sent to close a subflow because of an invalid response.
+        */
+       SK_RST_REASON_MPTCP_RST_EMPTCP,
+       /* Lack of resources.
+        * This code indicates that the sending host does not have enough
+        * resources to support the terminated subflow.
+        */
+       SK_RST_REASON_MPTCP_RST_ERESOURCE,
+       /* Administratively prohibited.
+        * This code indicates that the requested subflow is prohibited by
+        * the policies of the sending host.
+        */
+       SK_RST_REASON_MPTCP_RST_EPROHIBIT,
+       /* Too much outstanding data.
+        * This code indicates that there is an excessive amount of data
+        * that needs to be transmitted over the terminated subflow while
+        * having already been acknowledged over one or more other subflows.
+        * This may occur if a path has been unavailable for a short period
+        * and it is more efficient to reset and start again than it is to
+        * retransmit the queued data.
+        */
+       SK_RST_REASON_MPTCP_RST_EWQ2BIG,
+       /* Unacceptable performance.
+        * This code indicates that the performance of this subflow was
+        * too low compared to the other subflows of this Multipath TCP
+        * connection.
+        */
+       SK_RST_REASON_MPTCP_RST_EBADPERF,
+       /* Middlebox interference.
+        * Middlebox interference has been detected over this subflow,
+        * making MPTCP signaling invalid. For example, this may be sent
+        * if the checksum does not validate.
+        */
+       SK_RST_REASON_MPTCP_RST_EMIDDLEBOX,
+
+       /* For the real standalone socket reset reason, we start from here */
+       SK_RST_REASON_NOT_SPECIFIED,
+
+       /* Maximum of socket reset reasons.
+        * It shouldn't be used as a real 'reason'.
+        */
+       SK_RST_REASON_MAX,
+};
+
+static inline int convert_mptcp_reason(int reason)
+{
+       return reason += RST_REASON_START;
+}
+#endif
-- 
2.37.3


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