Otherwise valid code can panic on workspace exhaustion:

    std.ip(req.http.X-Real-IP, std.ip(req.http.X-Client-IP, client.ip))

If the nested std.ip() call runs out of workspace, it will return a null
ip instead of the fallback, and since the outer std.ip() call is getting
a fallback argument, it will panic upon checking the suckaddr sanity.

Refs a3b26d0b

{req,bereq}.time remain constant across restarts/retries
req_top.time remains constant across esi includes

The other values represent the time when the respective object
was created.

(Last part of #3599)

(4th part of #3599)

(3rd part of #3599)

(2nd part of #3599)

(First part of #3599)

Dont limit ourselves to a set number of VSL records to include
the "0 CLI" we want, various platforms emit a number of Debug
messages relating to sockopt

Use the `process p%d -expect-text` mechanism to wait only as
long as necessary for the "0 CLI"

Dont limit ourselves to a set number of VSL records to include
the "0 CLI" we want, various platforms emit a number of Debug
messages relating to sockopt

Use the `process p%d -expect-text` mechanism to wait only as
long as necessary for the "0 CLI"

Refs #3740

Closes #3692

Conflicts:
	bin/varnishd/cache/cache_acceptor.c

Instead of having a single global check that all acceptors may race
towards, this check now happens on a per listen socket basis. For
sockets with a different inheritance behavior on a single system, we
avoid having the first connection dictate what may be inherited by
a connection socket from its listen socket for all the other listen
addresses.

At least on Linux, Unix-domain sockets DO NOT inherit options like
SO_{RCV,SND}TIMEO even though TCP sockets do. On the off chance that
even sockets of the same family could behave differently, like for
example a regular vs a loopback TCP session, this is done on a per
listen address basis. To avoid cache-acceptor coordination with the
acceptor worker threads of a given listen address, workers will
individually perform this check once and for all when the first
connection is accepted.

We also stay defensive in the event of a parameter change, just in
case a previous test would assume inheritance because the Varnish
parameter value would match the kernel default value. Once a mismatch
is observed for a given connection with a given socket, the inheritance
test is no longer performed needlessly for this combination.

A race still exists between acceptors from different thread pools for
a given listen address, but this race is identical to the previous one
based on the former global need_test variable.

Although the inheritance check leaks into struct listen_sock, it is
opaque so everything can remain contained inside cache_acceptor.c.

Some aspects of this change (including the clarification comments) are
from @mbgrydeland.

Refs #2722

And while at it, update the SO_LINGER explanation to match reality.

Refs 7eba9460

Conflicts:
	bin/varnishd/cache/cache_acceptor.c

The SO_KEEPALIVE justification used to precede such a constant and was
left confusingly lingering over the unrelated need_test variable.

Conflicts:
	bin/varnishd/cache/cache_acceptor.c

Using the tmp sock_arg for storage, we can test all values with the same
logic and only differentiate hard-coded options from parameterized ones.

Stylistic polish by @mbgrydeland.

Conflicts:
	bin/varnishd/cache/cache_acceptor.c

They can be stored directly in the sock_opts array or on the stack.

Conflicts:
	bin/varnishd/cache/cache_acceptor.c

The sess and listen_sock structs contain everything we need to find or
infer the former `sock`, `uds` and `force` arguments. In particular, it
helps distinguish between working on a connection vs listen socket.

And conversely rename `to` variables to `so` for consistency.

Better diff with the --word-diff --word-diff-regex='\w+' options.

Conflicts:
	bin/varnishd/cache/cache_acceptor.c

It is a 1:1 mapping with IPPROTO_TCP, so TCP_NODELAY was moved down to
be with the other IPPROTO_TCP options.

Conflicts:
	bin/varnishd/cache/cache_acceptor.c

Instead of having a single global check that all acceptors may race
towards, this check now happens on a per listen socket basis. For
sockets with a different inheritance behavior on a single system, we
avoid having the first connection dictate what may be inherited by
a connection socket from its listen socket for all the other listen
addresses.

At least on Linux, Unix-domain sockets DO NOT inherit options like
SO_{RCV,SND}TIMEO even though TCP sockets do. On the off chance that
even sockets of the same family could behave differently, like for
example a regular vs a loopback TCP session, this is done on a per
listen address basis. To avoid cache-acceptor coordination with the
acceptor worker threads of a given listen address, workers will
individually perform this check once and for all when the first
connection is accepted.

We also stay defensive in the event of a parameter change, just in
case a previous test would assume inheritance because the Varnish
parameter value would match the kernel default value. Once a mismatch
is observed for a given connection with a given socket, the inheritance
test is no longer performed needlessly for this combination.

A race still exists between acceptors from different thread pools for
a given listen address, but this race is identical to the previous one
based on the former global need_test variable.

Although the inheritance check leaks into struct listen_sock, it is
opaque so everything can remain contained inside cache_acceptor.c.

Some aspects of this change (including the clarification comments) are
from @mbgrydeland.

Refs #2722

And while at it, update the SO_LINGER explanation to match reality.

Refs 7eba9460