Feat: Epoll P2P Implementation

[Gursukh]

core/net: back P2P sockets with real host sockets and unify epoll handling

Move P2P socket behavior onto actual UDP/TCP file descriptors instead of stubbed flow.
P2P sockets now own a real native socket, expose it through Native(), track socket type/non-blocking state/vport, and close cleanly on teardown.

Rewrite P2P operations to delegate to the OS:

bind/connect with address conversion and vport tracking
send/recv paths via sendto/sendmsg and recvfrom/recvmsg
socket option get/set through converted levels, including PS4-specific handling
accept returns a wrapped real accepted fd
getsockname/getpeername now return real endpoint data
Also clean up shared networking internals by promoting common helper conversions, removing duplicate Unix-side helpers/macros, and dropping the old epoll eventfd drain path.
With Native() now returning real fds for P2P sockets, epoll handling is unified across socket types.

Fyi, didnt test on windows only linux. This was targeted for LBP

[Gursukh]

• Introduce NativeSocket between Socket and PosixSocket/UnixSocket to eliminate identical Close/Listen/fstat/IsValid/Native implementations
• Reduce P2PSocket from ~300 lines to ~80, inheriting everything else
• Fix msghdr reinterpret_cast corruption on 64-bit Linux (OrbisNetMsghdr uses int-sized fields vs native size_t) in both PosixSocket and UnixSocket via ConvertOrbisToNativeMsghdr helper
• Implement sceNetEpollAbort using eventfd on Linux + atomic flag
• Add P2P dgram epoll event filtering (EPOLLIN-only, matching PS4 kernel behavior discovered from decompilation)
• Fix SO_LINGER rejecting P2P stream sockets
• Fix NativeSocket::Close not invalidating the fd after close
• Use unique_ptr in EpollTable to avoid move-constructor issues with std::atomic members

[Gursukh]

• Add if (i >= maxevents) break guard in EpollWait event loop
• Windows: loopback UDP socket bound to 127.0.0.1, self-connected, registered in wepoll with sentinel data.fd = -1
• macOS/BSD: self-pipe via pipe() + O_NONBLOCK, read end registered in epoll with sentinel data.fd = -1
• Add (void) casts on write/read return values in Abort/ClearAbort
• Drain loops in ClearAbort for pipe/socket (handles multiple aborts)
• Rename epoll_events_mod to epoll_events for consistency with ADD path
• Restore libepoll-shim TODO comment for FreeBSD

[Randomuser8219]

Windows build fails with:

FAILED: [code=1] CMakeFiles/shadps4.dir/src/core/libraries/network/net_epoll.cpp.obj 
ccache C:\PROGRA~1\LLVM\bin\clang-cl.exe  /nologo -TP -DAL_LIBTYPE_STATIC -DBOOST_ASIO_STANDALONE -DENABLE_DISCORD_RPC -DHWINFO_EXPORTS -DIMGUI_USER_CONFIG=\"imgui/imgui_config.h\" -DMINIZ_STATIC_DEFINE -DNOMINMAX -DNTDDI_VERSION=0x0A000006 -DPUGIXML_NO_EXCEPTIONS -DTRACY_NO_CALLSTACK -DTRACY_NO_CODE_TRANSFER -DTRACY_NO_CONTEXT_SWITCH -DTRACY_NO_CRASH_HANDLER -DTRACY_NO_FRAME_IMAGE -DTRACY_NO_SAMPLING -DTRACY_NO_SYSTEM_TRACING -DTRACY_ONLY_LOCALHOST -DTRACY_ON_DEMAND -DWIN32_LEAN_AND_MEAN -DWINVER=0x0A00 -DZYCORE_STATIC_BUILD -DZYDIS_STATIC_BUILD -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_SCL_SECURE_NO_WARNINGS -D_TIMESPEC_DEFINED -D_WIN32_WINNT=0x0A00 -ID:\a\shadPS4\shadPS4\src -ID:\a\shadPS4\shadPS4 -ID:\a\shadPS4\shadPS4\build\src\video_core\host_shaders\include -ID:\a\shadPS4\shadPS4\build\src\imgui\renderer\generated_fonts -ID:\a\shadPS4\shadPS4\build\_cmrc\include -imsvcD:\a\shadPS4\shadPS4\externals\magic_enum\include -imsvcD:\a\shadPS4\shadPS4\externals\fmt\include -imsvcD:\a\shadPS4\sha
In file included from D:\a\shadPS4\shadPS4\src\core\libraries\network\net_epoll.cpp:8:
D:\a\shadPS4\shadPS4\src\core\libraries\network\net_epoll.h(40,25): error: use of undeclared identifier 'INVALID_SOCKET'
   40 |     SOCKET abort_sock = INVALID_SOCKET; // loopback UDP socket for abort wake
      |                         ^
1 error generated.

[StevenMiller123]

Seems to break Skullgirls. Just crashes silently after it starts it's P2P stuff.
CUSA01606.log

[Gursukh]

Seems to break Skullgirls. Just crashes silently after it starts it's P2P stuff. CUSA01606.log

Ran on Windows and get the silent crash pretty much every launch sometimes immediately sometimes after a minute.
This behaviour also exists the 0.15.0 release and current main branch, I don't believe my changes are responsible.

See attached log for same crash on main branch with old (stubbed) epoll P2P implementation.
CUSA01606.log

Both crashes in and not in my branch seem to be a failed assert in libusb/core.c:1278

[StevenMiller123]

Seemed to be crashing quicker than usual for me on this PR, which is why I pointed it out.
Ran it under a debugger and it just seems to be the libusb issues though, so disregard my comment.

[mikusp]

Thank you for your contribution @Gursukh. While it seems to work with LBP3, the core principle of P2P sockets is different on the real hardware, and it won't work for multiplayer communication.

The key differences are:

• AFAIK only SOCK_DGRAM can be used as the P2P socket as those need to be able to communicate over the internet and go through NATs
• STREAM_P2P is implemented as a user-level TCP layer over DGRAM_P2P
• communication over P2P sockets always uses a header with the vport embedded, so simply redirecting send/recv to OS functions is incorrect

There may be more differences, but I haven't looked into networking for some time now. RPCS3 contains a working implementation of P2P and it seems like it's almost the same as with PS4, so you can take a look at https://github.com/RPCS3/rpcs3/tree/master/rpcs3/Emu/Cell/lv2/sys_net If you have any questions feel free to ask here

[Gursukh]

Hey @mikusp, thanks for the feedback. I'll work on revising the approach. Can you recommend a game that would work well to test P2P connections?

[Hog185]

the last of us remastered has p2p for its factions mode, im aware of some weird graphical errors in the game but you can get in game on nightly