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MPTCP maintains a status bit, MPTCP_SEND_SPACE, that is set when at least one subflow and the mptcp socket itself are writeable. mptcp_poll returns EPOLLOUT if the bit is set. mptcp_sendmsg makes sure MPTCP_SEND_SPACE gets cleared when last write has used up all subflows or the mptcp socket wmem. This reworks nospace handling as follows: MPTCP_SEND_SPACE is replaced with MPTCP_NOSPACE, i.e. inverted meaning. This bit is set when the mptcp socket is not writeable. The mptcp-level ack path schedule will then schedule the mptcp worker to allow it to free already-acked data (and reduce wmem usage). This will then wake userspace processes that wait for a POLLOUT event. sendmsg will set MPTCP_NOSPACE only when it has to wait for more wmem (blocking I/O case). poll path will set MPTCP_NOSPACE in case the mptcp socket is not writeable. Normal tcp-level notification (SOCK_NOSPACE) is only enabled in case the subflow socket has no available wmem. Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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 Restructured Text 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.