[dpdk-dev] [PATCH] doc: announce renaming of rte_ether_hdr fields

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

It is proposed to rename fields of `struct rte_ether_hdr`,
`s_addr` tp `src_addr` and `d_addr` to `dst_addr`,
due to the clash with system macro on Windows.
Until remaining is done in 21.11, a workaround can be used.

Windows Sockets headers contain `#define s_addr S_un.S_addr`, which
conflicts with `s_addr` field of `struct rte_ether_hdr`. Undefining
this macro in <rte_ether.h> is breaking some usages of DPDK
and Windows headers in one file.

Example 1:

    #include <winsock2.h>
    #include <rte_ether.h>
    struct in_addr addr;
    /* addr.s_addr = 0;     ERROR: s_addr undefined by DPDK */

Example 2:

    #include <rte_ether.h>
    #include <winsock2.h>
    struct rte_ether_hdr eh;
    /* eh.s_addr.addr_bytes[0] = 0;     ERROR: `addr_s` is a macro */

It is not mandatory to rename `d_addr`, this is for consistency only.
Naming in `rte_ether_hdr` will also resemble `rte_ipv4/6_hdr`.

Workaround is to define `struct rte_ether_hdr` in such a away that
it can be used with or without `s_addr` macro (as defined on Windows)
This can be done for Windows only or for all platforms to save space.

    #pragma push_macro("s_addr")
    #ifdef s_addr
    #undef s_addr
    #endif

    struct rte_ether_hdr {
        struct rte_ether_addr d_addr; /**< Destination address. */
        RTE_STD_C11
        union {
            struct rte_ether_addr s_addr; /**< Source address. */
            struct {
                struct rte_ether_addr S_un;
                /**< MUST NOT be used directly, only via s_addr */
            } S_addr;
            /*< MUST NOT be used directly, only via s_addr */
        };
        uint16_t ether_type; /**< Frame type. */
    } __rte_aligned(2);

    #pragma pop_macro("s_addr")

Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
---
 doc/guides/rel_notes/deprecation.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
index 82c1a90a3..f7be10543 100644
--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst
@@ -125,3 +125,7 @@ Deprecation Notices
 * cmdline: ``cmdline`` structure will be made opaque to hide platform-specific
   content. On Linux and FreeBSD, supported prior to DPDK 20.11,
   original structure will be kept until DPDK 21.11.
+
+* net: ``s_addr`` and ``d_addr`` fields of ``rte_ether_hdr`` structure
+  will be renamed to ``src_addr`` and ``dst_addr`` respectively in DPDK 20.11
+  in order to avoid conflict with Windows Sockets headers.
-- 
2.29.2