With the `<zephyr/posix/...> prefix, it became
exponentially more difficult to integrate 3rd-party
libraries that depend on the POSIX API.

Standard POSIX headers should be available in standard
include paths - and that should most certainly the case
when `CONFIG_POSIX_API=y`.

With this change:

* When `CONFIG_POSIX_API=y`
  - applications have explicitly chosen to use
    POSIX APIs.
  - all standard POSIX includes are in the default
    include path.
* When `CONFIG_POSIX_API=n`
  - applications *may* include POSIX headers
    explicitly with the namespaced prefix
  - e.g. `#include <zephyr/posix/unistd.h>`
  - individual Kconfig options can be used to
    enable POSIX features selectively, such as
    `getopt` or `eventfd`.

Signed-off-by: Chris Friedt <[email protected]>

Rename the `posix_sched.h` to conform to the spec.

IEEE Std 1003.1

Signed-off-by: Chris Friedt <[email protected]>

The `pthread_key.h` header is nonstandard and is an
implementation detail of `pthread.h`.

Signed-off-by: Chris Friedt <[email protected]>

The `getopt()` function is part of POSIX and should be
available when applications choose to enable general POSIX
API support.

Signed-off-by: Chris Friedt <[email protected]>

Although the eventfd API is not (yet) a part of POSIX,
it's pretty well ubiquitous on POSIX systems now.

Enable it by default when `CONFIG_POSIX_API=y`.

Signed-off-by: Chris Friedt <[email protected]>

Newlib and PicoLibc both already alias `open` to `_open`.

Signed-off-by: Chris Friedt <[email protected]>

The `_exit()` function should be declared in `<unistd.h>`.

Signed-off-by: Chris Friedt <[email protected]>

The networking subsystem defines a rather large amount of POSIX
prototypes. However, it's done in a somewhat subversive way via

```
CONFIG_NET_SOCKETS_POSIX_NAMES
```

This option should be removed (or moved to POSIX) and the
networking implementations should be properly namespaced.

With that, the POSIX interface for network-related functions
can simply be a thin wrapper around the z-namespaced variants,
where applicable, or proper POSIX functions should actually
be moved to `lib/posix`.

This will also require a better solution to testing network
functionality on `native_posix` though. The ability to run
those tests and the supposed incompatibility between
`CONFIG_ARCH_POSIX` and `CONFIG_POSIX_API` was the main
motivation for adding `CONFIG_NET_SOCKETS_POSIX_NAMES`.

Eventually, with proper namespacing, these preprocessor
guards against redefining the same symbols can be
removed.

Signed-off-by: Chris Friedt <[email protected]>

The specification actually requires this to be a plain
`struct mq_attr`, without the typedef.

Signed-off-by: Chris Friedt <[email protected]>

The `<sys/ioctl.h>` header never actually declared
the `ioctl(2)` function prototype, so this fixes that.

Signed-off-by: Chris Friedt <[email protected]>

The spec requires that these two types be defined in
`<netinet/in.h>`.

Signed-off-by: Chris Friedt <[email protected]>

The spec requires that `in_addr_t` and `in_port_t` are both
defined when `<arpa/inet.h>` is included.

They were added to `<netinet/in.h>` in the previous commit.

Signed-off-by: Chris Friedt <[email protected]>

Constants like `EAI_SYSTEM` should be defined in `<netdb.h>`
according to the spec.

In Zephyr, they should be defined via appropriately
namespaced z-variants (currently `DNS_EAI_SYSTEM` and so on).

Signed-off-by: Chris Friedt <[email protected]>

The `FIONREAD` ioctl is usually used to query how many bytes
are available to read immediately from a specific file
descriptor. It's quite useful.

Define it here so that it can be used by applications.

Signed-off-by: Chris Friedt <[email protected]>

The spec requires `<sys/socket.h>` to declare
struct linger. Define it so that applications
and libraries do not get compile errors when
building against Zephyr.

Signed-off-by: Chris Friedt <[email protected]>

The `<netdb.h>` header typically defines `NI_MAXSERV` as a
reasonable default buffer size to use in applications that
use `getnameinfo()` to query a service name.

Most GNU and BSD systems define it by default so provide
it as a convenience so applications and 3rd-party libraries
do not encounter a compile error.

Signed-off-by: Chris Friedt <[email protected]>

The POSIX spec requires that `SO_LINGER`, `SO_RCVLOWAT`,
and `SO_SNDLOWAT`, and `SOMAXCONN` are defined in
`<sys/socket.h>`. However, most of the existing socket
options and related constants are defined in
`<zephyr/net/socket.h>`.

For now, we'll co-locate them. It would be
good to properly namespace things.

Additionally, a no-op for setsockopt for `SO_LINGER` to
make things Just Work (TM) for now.

Signed-off-by: Chris Friedt <[email protected]>

Add a trivial suite that simply ensures headers exist and that
they supply standard symbols and constants.

These tests are intended to be ordered exactly as the respective
feature appears in the respective specification at

https://pubs.opengroup.org/onlinepubs/9699919799

Over time, as POSIX support improves, we can enable additional
checks.

If `CONFIG_POSIX_API=n`, then we simply ensure that the header
can be included, that constants and structures exist, including
the existence of required fields in each structure.

We check that a constant exist, by comparing its value against
an arbitrary number. If the constant does not exist, it would
of course be a compile error.

```
zassert_not_equal(-1, POLLIN);
```

We check that a structure contains required fields by
comparing the field offset with an arbitrary number. If
the field does not exist, of course, there would be a
compile error.

```
zassert_not_equal(-1, offsetof(struct pollfd, fd));
```

For non-scalar constants, we simply attempt to assign
a value to the specific type:

```
struct in6_addr any6 = IN6ADDR_ANY_INIT;
```

If `CONFIG_POSIX_API=y`, then we additionally check that required
functions are non-NULL (limited to what is currently supported in
Zephyr).

```
zassert_not_null(pthread_create);
```

Note: functional verification tests should be done outside of this
test suite.

Signed-off-by: Chris Friedt <[email protected]>

Only include `<fcntl.h>` for `CONFIG_ARCH_POSIX`. Otherwise,
include `<zephyr/posix/fcntl.h>`.

Signed-off-by: Chris Friedt <[email protected]>

`<fcntl.h>`, `<net/if.h>`, and `<netinet/tcp.h>` were missing
`extern "C" { .. }"` which is required to avoid C++ name
mangling.

Signed-off-by: Chris Friedt <[email protected]>