docs: net: description of MSG_ZEROCOPY for AF_VSOCK

This adds description of MSG_ZEROCOPY flag support for AF_VSOCK type of
socket.

Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

docs: net: fix inaccuracies in msg_zerocopy.rst

Replace "sendpage" with "sendfile". Remove comment about
ENOBUFS when the sockopt hasn't been set; experimentation
indicates that this is not true.

Signed-off-by: nick black <dankamongmen@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/Y/gg/EhIIjugLdd3@schwarzgerat.orthanc
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

docs: use the lore redirector everywhere

Change all links from using the lkml redirector to the lore redirector,
as the kernel.org admin recently indicated: we shouldn't be using
lkml.kernel.org anymore because the domain can create confusion, as it
indicates it is only valid for messages sent to the LKML; the convention
has been to use https://lore.kernel.org/r/msgid for this reason.

In this process also change three links from using http to https.

Link: https://lore.kernel.org/r/20211006170025.qw3glxvocczfuhar@meerkat.local
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: Borislav Petkov <bp@alien8.de>
CC: Hu Haowen <src.res@email.cn>
CC: Alex Shi <alexs@kernel.org>
CC: Federico Vaga <federico.vaga@vaga.pv.it>
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Reviewed-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Link: https://lore.kernel.org/r/5bb55bac6ba10fafab19bf2b21572dd0e2f8cea2.1633593385.git.linux@leemhuis.info
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

doc: fix link to MSG_ZEROCOPY patchset

Use https and link to the patch directly.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

doc: Mention MSG_ZEROCOPY implementation for UDP

MSG_ZEROCOPY implementation for UDP was merged in v5.0,
6e360f733113 ("Merge branch 'udp-msg_zerocopy'").

Signed-off-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

sock: remove zerocopy sockopt restriction on closed tcp state

Socket option SO_ZEROCOPY determines whether the kernel ignores or
processes flag MSG_ZEROCOPY on subsequent send calls. This to avoid
changing behavior for legacy processes.

Limiting the state change to closed sockets is annoying with passive
sockets and not necessary for correctness. Once created, zerocopy skbs
are processed based on their private state, not this socket flag.

Remove the constraint.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

doc: clarification about setting SO_ZEROCOPY

Signed-off-by: Kornilios Kourtis <kou@zurich.ibm.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

doc: document MSG_ZEROCOPY

Documentation for this feature was missing from the patchset.
Copied a lot from the netdev 2.1 paper, addressing some small
interface changes since then.

Changes
v1 -> v2
- change email discussion URL format
- clarify that u32 counter is per-syscall, unsigned and
wraps after UINT_MAX calls
- describe errno on send failure specific to MSG_ZEROCOPY
- a few very minor rewordings

Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>