[PATCH mptcp-next v2 0/4] Add MPTCP support for NBD

[Geliang Tang <geliang@kernel.org>]

From: Geliang Tang <tanggeliang@kylinos.cn>

This series adds MPTCP (Multipath TCP) support to NBD (Network Block
Device) and includes comprehensive tests.

MPTCP can aggregate bandwidth from multiple network interfaces, providing
significant performance improvements in multi-NIC scenarios. Our tests
with 4 virtual NICs (each limited to 1000 Mbit/s / 125 MB/s) show ~4x
bandwidth improvement: TCP achieves ~110 MiB/s while MPTCP achieves
~400 MiB/s for both read and write operations.

Patch 1 gives MPTCP sockets a distinct lockdep class to prevent
false positive lockdep warnings when MPTCP master sockets and their
subflow sockets are used together in the same lock chain.

Patch 2 adds a set_memalloc protocol callback to struct proto that
allows protocols to propagate SOCK_MEMALLOC flag and allocation
settings to their sub-sockets automatically. MPTCP implements this
callback to sync memalloc settings to all subflow sockets.

Patch 3 adds MPTCP socket support to the kernel NBD driver by
allowing MPTCP sockets in nbd_get_socket().

Patch 4 adds a comprehensive test script (mptcp_nbd.sh) that
validates NBD over both TCP and MPTCP.

v2:
- Add lockdep class distinction for MPTCP sockets (patch 1)
- Add set_memalloc protocol callback for automatic subflow sync (patch 2)
- update selfetsts.

v1:
- https://patchwork.kernel.org/project/mptcp/cover/cover.1792746800.git.tanggeliang@kylinos.cn/

Geliang Tang (4):
  mptcp: give MPTCP sockets a distinct lockdep class
  sock: add set_memalloc protocol callback
  nbd: allow MPTCP sockets
  selftests: mptcp: add mptcp nbd tests

 drivers/block/nbd.c                           |   5 +-
 include/net/sock.h                            |   1 +
 net/core/sock.c                               |   8 +
 net/mptcp/pm_kernel.c                         |  16 -
 net/mptcp/protocol.c                          |  58 ++-
 tools/testing/selftests/net/mptcp/Makefile    |   1 +
 tools/testing/selftests/net/mptcp/config      |   1 +
 .../testing/selftests/net/mptcp/mptcp_lib.sh  |  13 +
 .../testing/selftests/net/mptcp/mptcp_nbd.sh  | 373 ++++++++++++++++++
 9 files changed, 458 insertions(+), 18 deletions(-)
 create mode 100755 tools/testing/selftests/net/mptcp/mptcp_nbd.sh

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2.55.0