Re: [dpdk-dev] [PATCH] eal/windows: add sys/queue.h.

[Nick Connolly <nick.connolly@mayadata.io>]

> diff --git a/lib/eal/windows/include/meson.build b/lib/eal/windows/include/meson.build
> index b3534b025f..875cc1cf0d 100644
> --- a/lib/eal/windows/include/meson.build
> +++ b/lib/eal/windows/include/meson.build
> @@ -8,3 +8,7 @@ headers += files(
>           'rte_virt2phys.h',
>           'rte_windows.h',
>   )
> +
> +sys_headers = []
> +subdir('sys')
> +install_headers(sys_headers, subdir: 'sys')
> diff --git a/lib/eal/windows/include/sys/meson.build b/lib/eal/windows/include/sys/meson.build
> new file mode 100644
> index 0000000000..6896cbf678
> --- /dev/null
> +++ b/lib/eal/windows/include/sys/meson.build
> @@ -0,0 +1,6 @@
> +# SPDX-License-Identifier: BSD-3-Clause
> +# Copyright 2021 VMware, Inc
> +
> +sys_headers += files(
> +        'queue.h',
> +)

Hi William,

If I've understood this change correctly it will create a sys/queue.h 
header in the build/include folder.
This seems like a reasonable approach to handle missing functionality, 
but unfortunately it is problematic.

An application that links against DPDK is likely to be dealing with 
similar issues with missing functionality
and providing a definition in the DPDK includes can conflict with the 
approach taken by the application
(in this instance there could be two versions of sys/queue.h in the 
include paths leading to ambiguity).

After discussion, the approach adopted by the DPDK community is that:

  * DPDK should depend only on the C library and not require POSIX
    functionality from the underlying
    system (headers, definitions etc). Missing functionality should be
    implemented within the DPDK
    code.
  * DPDK should not export POSIX functionality into the environment
    (symbols, macros, headers etc)
    to avoid these definitions clashing with the application.

In this instance, it seems that rte_log.h depends upon the system having 
sys/queue.h which is not
a standard C dependency. The appropriate response here (based on the 
above approach) is to remove
the sys/queue.h dependency from rte_log.h and ensure that it only 
depends upon rte_* definitions
contained within the DPDK.

Regards,
Nick