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James Chapman says: ==================== l2tp: don't use the tunnel socket's sk_user_data in datapath This series refactors l2tp to not use the tunnel socket's sk_user_data in the datapath. The main reasons for doing this are * to allow for simplifying internal socket cleanup code (to be done in a later series) * to support multiple L2TPv3 UDP tunnels using the same 5-tuple address When handling received UDP frames, l2tp's current approach is to look up a session in a per-tunnel list. l2tp uses the tunnel socket's sk_user_data to derive the tunnel context from the receiving socket. But this results in the socket and tunnel lifetimes being very tightly coupled and the tunnel/socket cleanup paths being complicated. The latter has historically been a source of l2tp bugs and makes the code more difficult to maintain. Also, if sockets are aliased, we can't trust that the socket's sk_user_data references the right tunnel anyway. Hence the desire to not use sk_user_data in the datapath. The new approach is to lookup sessions in a per-net session list without first deriving the tunnel: * For L2TPv2, the l2tp header has separate tunnel ID and session ID fields which can be trivially combined to make a unique 32-bit key for per-net session lookup. * For L2TPv3, there is no tunnel ID in the packet header, only a session ID, which should be unique over all tunnels so can be used as a key for per-net session lookup. However, this only works when the L2TPv3 session ID really is unique over all tunnels. At least one L2TPv3 application is known to use the same session ID in different L2TPv3 UDP tunnels, relying on UDP address/ports to distinguish them. This worked previously because sessions in UDP tunnels were kept in a per-tunnel list. To retain support for this, L2TPv3 session ID collisions are managed using a separate per-net session hlist, keyed by ID and sk. When looking up a session by ID, if there's more than one match, sk is used to find the right one. L2TPv3 sessions in IP-encap tunnels are already looked up by session ID in a per-net list. This work has UDP sessions also use the per-net session list, while allowing for session ID collisions. The existing per-tunnel hlist becomes a plain list since it is used only in management and cleanup paths to walk a list of sessions in a given tunnel. For better performance, the per-net session lists use IDR. Separate IDRs are used for L2TPv2 and L2TPv3 sessions to avoid potential key collisions. These changes pass l2tp regression tests and improve data forwarding performance by about 10% in some of my test setups. ==================== Signed-off-by: David S. Miller <davem@davemloft.net> |
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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.