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docs: tls: document the TLS_TX_ZEROCOPY_RO

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Add missing documentation for the TLS_TX_ZEROCOPY_RO opt-in.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Link: https://lore.kernel.org/r/20220610180212.110590-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
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Jakub Kicinski 2022-06-10 11:02:12 -07:00 committed by Paolo Abeni
parent 19d62f5eea
commit 7e5e8ec7db
1 changed files with 25 additions and 0 deletions
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Documentation/networking/tls.rst
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@ -214,6 +214,31 @@ of calling send directly after a handshake using gnutls.
Since it doesn't implement a full record layer, control
messages are not supported.
Optional optimizations
----------------------
There are certain condition-specific optimizations the TLS ULP can make,
if requested. Those optimizations are either not universally beneficial
or may impact correctness, hence they require an opt-in.
All options are set per-socket using setsockopt(), and their
state can be checked using getsockopt() and via socket diag (``ss``).
TLS_TX_ZEROCOPY_RO
~~~~~~~~~~~~~~~~~~
For device offload only. Allow sendfile() data to be transmitted directly
to the NIC without making an in-kernel copy. This allows true zero-copy
behavior when device offload is enabled.
The application must make sure that the data is not modified between being
submitted and transmission completing. In other words this is mostly
applicable if the data sent on a socket via sendfile() is read-only.
Modifying the data may result in different versions of the data being used
for the original TCP transmission and TCP retransmissions. To the receiver
this will look like TLS records had been tampered with and will result
in record authentication failures.
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