The last thing between the host-framed surface and a run: the sub-byte on the wire that names it.
ServerOwned had one (7) and the host frame had none, so the encoder refused the op with
UnknownWindowKind - a correct refusal, and the reason the first run of MOBILEGL_IPC_SURFACE=host
failed in the codec rather than anywhere near the pixels.
- protocol.fbs: WindowKind::HostFrame = 8, appended, legal on CreateWindowSurface only and always
with nativeToken 0 - the same rules ServerOwned carries, for the same reason: no pointer of any
process's window system crosses (Rule G/H).
- SurfaceRefusal: HostFrameOnSetWindowHandle = 5, its own code rather than reusing the
server-owned one: a refusal that names the wrong owner sends the next reader to the wrong place.
- SurfaceOpCodec: the encode and decode arms, the two wire errors that go with them
(HostFrameTokenNotZero latches as corruption, HostFrameOnSetWindowHandle is a named refusal), and
the range bound that had ServerOwned as its upper limit now ends at HostFrame.
- protocol_generated.h regenerated with the pinned submodule's flatc (scripts/gen_protocol.py),
diff being exactly the two appended enumerators.
Both ends must be rebuilt together, as any protocol revision here: the container's client and the
device's server went out with this on either side.
Step three of CONTRACT-P6 5.2, the funnel's whole point: instead of the peer
reading a bare EOF and guessing, the session publishes a SessionFault frame
that names the family before it aborts.
THE WIRE CHANGE IS D2's, exactly: `table Fatal` appends `family: string`,
append-only, so an older peer still reads `code` and `message`. `code` stays
the coarse seven-value projection; `family` carries the full word.
SessionFail publishes it before the abort, on whichever session's control
plane is active - the client has a ClientSession, the server a ServerSession,
so under spawn the frame reaches the far side whichever role is dying. Under
inproc both exist and it goes to an in-process transport the aborting process
will never read, which is harmless and cheaper than a special case that would
then be the untested one. Best-effort by nature: this thread is about to die,
so a send that blocks or fails changes nothing.
seq/op from the prose are NOT threaded through the 90 sites: the message
already names the op where it matters, so the frame carries what it can name
honestly (code, family, message) rather than a field that is always zero.
The client recognizes it: RunRemoteSurfaceControlFrame's reply loop, which
already demuxes CapsSnapshot from SurfaceReply, gains a Fatal arm that logs the
family and detail, latches device-lost from it, and returns transport-closed.
A server that DETECTS a fatal condition and aborts itself now tells the client
why; a kill -9 still bypasses abort entirely and is caught by dl's hangup
witness instead - the two cover the two ways a server can die.
The census learns SessionFail: a SessionFail call, like a WireLogFatal call,
must carry a Fatal{ word in its string, so the enum and the string cannot
disagree. FatalFunnel.{h,cpp} join the funnel exemption. Baseline is 4 aborts.
FatalFamilyTest gains the wire round-trip: every family's frame carries its
word and its projected code across encode/verify/decode.
G1 re-measured after the schema change: 0 symbol diff, .text unchanged at
0xa52203. Unit 2359 (one pre-existing environmental failure), integration-split
186/186, integration-spawn 102/102, retrace 6/6, census 0 unmarked.
OpenRA.DirectGLES.SPAWN is green: ssim=1.000000, mismatchPixels=0, zero
Fatal{ lines, against a server in a process the client started by name. The
inproc SPLIT arm stays beside it as the control, so "did the transport break
it" and "did the phase break it" remain separately answerable.
Five defects stood between the handshake and that picture. Each one was
silent in its own way, and none of them looked like what it was.
1. THE DOORBELL COULD NOT WAKE ITSELF. SocketDoorbell's one-fd form sends on
the end it polls, so a write is delivered to the PEER - correct for waking
the other process, useless for waking a thread in this one. The server's
control pump posts into the apply thread's mailbox and must ring the bell
that thread parks on. Symptom: every eglInitialize crossed, landed in the
mailbox, and timed out at 5 s. The two-fd form (park on [0], notify on [1])
is restored here, and the bell handover goes from two descriptors to THREE
- the client needs the same split for the same reason. Seven offers now.
2. InitCapabilities HAD NO WIRE KIND. CONTRACT-P6 §2 predicted this exactly
("the request has a live client caller and the codec refuses to encode
it"). SurfaceOpKind gains 11, append-only; the decode range's upper bound
moves with it, or the new tag reads as out-of-range and surfaces as
Fatal{ProtocolCorruption} rather than the missing row it is. The op's name
loses its InprocOnly suffix, which stopped being true here.
3. THE CHILD LOADED NO CONFIG AT ALL. mobilegl_server_main calls
InitServerRoleForSpawn directly, and MG_ConfigLoader::Init is a step of
MobileGL::Initialize - so every MG_Config value in the server was its
static default. MOBILEGL_BACKEND_TYPE survives the launcher's scrub on
purpose and was read by nobody: a DirectVulkan session would have brought
up a DirectGLES server and then disagreed with its client about which
backend the capability mask describes.
4. AND THEREFORE Transport READ AS Monolith, which CONTRACT-P6 §3.1 (D1)
forbids in as many words. a6 measured the cost: 226 live lines test
`Transport != Monolith` to select the SERVER arm, 148 in MG_Backend.
Monolith flips all of them to frontend glue in the one process with no
frontend. Observed precisely as predicted - UnitTexturesByHandle() answered
false, Clear took the legacy arm that dereferences borrowed FRONTEND slot
pointers, and the apply thread took a SIGSEGV inside SyncNeccessaryTextures
on the first Clear record of the trace. It is pinned in-process rather than
through the environment because the environment is where it must NOT be:
LooksLikeAClientEnvironment exits 65 on a surviving MOBILEGL_TRANSPORT, and
that check is anti-recursion catch (b). Dial, not Transport, is that axis.
5. THE LOG WAS CORRUPT, NOT MERELY INTERLEAVED. Two processes opened the same
MOBILEGL_LOG_FILE_PATH with "w" and each carried its OWN file offset, so
they overwrote each other's bytes - half-lines like `ote client: CapsMirror
generation 1 adopted`, and the server's whole startup block vanishing under
the client's later writes. This cost real diagnosis time twice, because a
missing line read as a code path not taken. O_APPEND now; the client still
truncates once so a fresh run is not a pile of old ones, and the server
never does - it would delete the very startup lines a failed session needs.
run_trace_case.cmake's Fatal{ census reads exactly this file, so it was
also reading a lie.
The retrace runner's split assertions become transport-aware: one row per
transport it admits, and a transport with no row is a FATAL rather than a
fall-through, because the fall-through is the accident the block exists to
prevent. The spawn row carries a SECOND sentence and it is the stronger half
- ConfigLoader's marker proves the value RESOLVED, while `spawn ARMED - the
server role runs in pid N` is written only after the launch, the connect and
the handshake all succeeded, and carries a pid that is not this process's.
inproc resolves its own marker while running the server role on a thread
here; nothing on that path can write this one.
G14: one test name added (TheEleventhFramedOpIsInitCapabilitiesAndItCrosses-
TheWire), none removed. The ten-op table keeps its name and its scope rather
than being renamed to eleven.
Two unit failures predate this change and are environmental in this tree:
PipeCatalogue.FrontendNeverTakesAnApplierAddress (the frontend source root
resolves empty) and SessionHandshakeTest.TheAbiFingerprintChangesWhenAnyOf-
ItsInputsDoes (GIT_COMMIT_HASH_SHORT is empty here, which a6 already recorded
as red in this configuration).
The twelve Server* forwarders' one-slot mailbox carried a raw function
pointer plus a void* to a stack-local Args struct (P5c audit row G4);
neither means anything across a process boundary. The slot now carries
one SurfaceControlFrame by value: kind is the op, scalars are the
arguments, and ok/eglMajor/eglMinor come back in the same value. The
blocking handshake, the shadow, the doorbell order and the C2 exit
block are unchanged.
- protocol.fbs: append-only - SurfaceOpKind gains SetSwapInterval=8,
ReleaseResources=9, SetWindowHandle=10; WindowKind gains MetalLayer=6;
SurfaceOp gains readSurface and context (the MakeCurrent four-tuple).
protocol_generated.h regenerated with the pinned flatc.
- Server/SurfaceControlFrame.{h,cpp}: the frame (trivially copyable by
static_assert) and the op enum - ten wire kinds plus four inproc-only
kinds (InitCapabilities is answered by CapsSnapshot on the wire,
SwapBuffers/InitWindowSurface have no production caller - f0-egl F8,
kept for the inproc test lane).
- Protocol/SurfaceOpCodec.{h,cpp}: the frame <-> SurfaceOp/SurfaceReply
codec, the explicit WindowBackend <-> WindowKind table, and the wire
entry ServerApplyWireSurfaceOp whose refusals are named:
Fatal{UnmigratedSurface, "AndroidNativeWindow@P12"} and
Fatal{ProtocolCorruption, "SurfaceOp"}.
- ServerLoop: RunOnApplyThread(fn, void*) -> RunSurfaceControlFrame(frame)
plus the dispatch ApplySurfaceControlFrame; the old per-forwarder Args
bodies moved into the dispatch unchanged (C7/ID-54, N-3, R-12 included).
RunProbeOnApplyThreadForTesting is the test seam through the same
channel (the hook lives in a member, never in the slot).
- Tests: RemoteClientTest/ServerLoopTest migrated to the probe seam; new
SurfaceControlFrameTest suite (mapping tables, wire round-trips, the
two named refusals) plus ServerLoopTest's AVoidForwarderCrossesAsOne-
DispatchedFrame (the frame channel's red-once handle) and
ServerLoopEglTest's TheInitializeDisplayReplyArrivesThroughTheFrame.
- 3rdparty/flatbuffers submodule pinned to the latest release tag v25.12.19 (7e163021). The runtime is header-only, so only 3rdparty/flatbuffers/include is ever used and no library is linked; CMake never calls add_subdirectory on it and flatc is not in the build graph (plan B section 8.1, inheriting the earlier plan's section 7.1).
- MobileGL/MG_Remote/Protocol/protocol.fbs carries the CONTROL PLANE only: SegmentRef, Hello, Welcome, CapsSnapshot, DefaultFramebufferInfo, SurfaceOp, SurfaceReply, ResyncRequest, ResyncDone, AuxRequest, Fatal, LogLine, union CtrlMsg and the CtrlEnvelope root with a file_identifier. Hot-path records are FlatBuffers structs generated from MG_Pipe/PipeCalls.def in a later package and are deliberately absent here, so record numbering never churns.
- Two deviations from the earlier plan's section 7.1 sketch, both deliberate: (a) ProgramReflection is not a union member - plan B ships program artifacts inside the create_shader_state CSO blob (section 8.2), and union tags are wire values that may only ever be appended, so reserving a tag for a message that may never exist is worse than appending one later; (b) maxComputeWorkGroupCount/Size are vectors, not [int:3] - fixed-size arrays are legal only in FlatBuffers structs, never in tables.
- scripts/gen_protocol.py resolves flatc as MOBILEGL_FLATC_EXECUTABLE, otherwise builds the pinned flatc ONCE into <repo>/../flatc-build (override with MOBILEGL_FLATC_BUILD_DIR), outside the project build graph. A flatc found on PATH is deliberately refused and a version mismatch against the pinned runtime is a hard error: the generated header static_asserts FLATBUFFERS_VERSION, so a stray flatc either fails to compile or churns the committed file on every machine. The earlier branch did the opposite - Protocol/CMakeLists.txt:22-38 add_subdirectory'd the FlatBuffers tree with FLATBUFFERS_BUILD_FLATC=ON whenever MOBILEGL_FLATC_EXECUTABLE was unset, which is exactly the NDK trap it claimed to avoid (cross-compile an arm64 flatc, then run it on the host).
- protocol_generated.h is committed with the project source header prepended by the generator, so regeneration is byte-identical: verified by running gen_protocol.py twice and by perturbing the file and regenerating it back.
- Reuse from Feat/CS-Delta-IPC: MobileGL/Protocol/mg_protocol_base.h, kept as the shared C vocabulary (result codes, byte spans, shm region, id typedefs) and keeping the structSize-first versioning discipline that section 14.2 calls the answer to risk B-R10. Dropped from it: MobileGLObjectKind / MobileGLObjectScope / MobileGLObjectHandle - plan B never puts GL object identity on the wire (the frontend allocates {slot, generation} handles in MG_Pipe, section 4.2.1), so a second identity vocabulary would be a drift surface with no reader. Added MOBILEGL_ERR_BUFFER_TOO_SMALL as an append-only code for the receive contract.
gold
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