Add minimal ebpf support for discontiguous frames

src/xdp/program.c

@@ -223,12 +223,18 @@ XdpInvokeEbpf(
     ASSERT((FragmentRing == NULL) || (FragmentExtension != NULL));
 
     //
-    // Fragmented frames are currently not supported by eBPF.
+    // Fragmented frames require special handling for eBPF programs using direct
+    // packet access. On Linux, the program must be loaded with a specific flag
+    // in order to inspect discontiguous packets. On Windows, discontiguous
+    // frames are always inspected by default, at least until a program flag API
+    // is supported by eBPF-for-Windows.
+    //
+    // https://github.com/microsoft/ebpf-for-windows/issues/3576
+    // https://github.com/microsoft/xdp-for-windows/issues/517
     //
     if (FragmentRing != NULL &&
         XdpGetFragmentExtension(Frame, FragmentExtension)->FragmentBufferCount != 0) {
-        RxAction = XDP_RX_ACTION_DROP;
-        goto Exit;
+        STAT_INC(RxQueueStats, InspectFramesDiscontiguous);
     }
 
     Buffer = &Frame->Buffer;

src/xdppcw/inc/xdppcw.h

@@ -19,6 +19,7 @@ typedef struct _XDP_PCW_RX_QUEUE {
     UINT64 InspectFramesDropped;
     UINT64 InspectFramesRedirected;
     UINT64 InspectFramesForwarded;
+    UINT64 InspectFramesDiscontiguous;
 } XDP_PCW_RX_QUEUE;
 
 typedef struct _XDP_PCW_LWF_RX_QUEUE {

src/xdppcw/xdppcw.man

@@ -145,6 +145,19 @@
             detailLevel="standard"
             defaultScale="1"
             />
+          <counter
+            id="10"
+            uri="Microsoft.Xdp.RxQueue.InspectFramesDiscontiguous"
+            name="Inspection Frames Discontiguous"
+            nameID="2040"
+            field="InspectFramesDiscontiguous"
+            description="Frames inspected by XDP with discontiguous data."
+            descriptionID="2042"
+            type="perf_counter_rawcount"
+            aggregate="sum"
+            detailLevel="standard"
+            defaultScale="1"
+            />
         </counterSet>
         <counterSet
           guid="{10672701-093b-4b91-8b76-8f53afd07cd0}"

test/functional/lib/tests.cpp

@@ -4790,17 +4790,15 @@ GenericRxEbpfFragments()
 {
     auto If = FnMpIf;
     unique_fnmp_handle GenericMp;
-    unique_fnlwf_handle FnLwf;
     const UINT32 Backfill = 3;
     const UINT32 Trailer = 4;
     const UINT32 SplitAt = 4;
     DATA_BUFFER Buffers[2] = {};
     const UCHAR Payload[] = "123GenericRxEbpfFragments4321";
 
-    unique_bpf_object BpfObject = AttachEbpfXdpProgram(If, "\\bpf\\pass.sys", "pass");
+    unique_bpf_object BpfObject = AttachEbpfXdpProgram(If, "\\bpf\\l1fwd.sys", "l1fwd");
 
     GenericMp = MpOpenGeneric(If.GetIfIndex());
-    FnLwf = LwfOpenDefault(If.GetIfIndex());
 
     Buffers[0].DataLength = SplitAt;
     Buffers[0].DataOffset = Backfill;
@@ -4811,26 +4809,24 @@ GenericRxEbpfFragments()
     Buffers[1].BufferLength = Buffers[1].DataLength + Trailer;
     Buffers[1].VirtualAddress = Payload + Buffers[0].BufferLength;
 
-    RX_FRAME Frame;
-    RxInitializeFrame(&Frame, FnMpIf.GetQueueId(), Buffers, RTL_NUMBER_OF(Buffers));
-
-    std::vector<UCHAR> Mask(sizeof(Payload) - Backfill - Trailer, 0xFF);
-    LwfRxFilter(FnLwf, Payload + Backfill, &Mask[0], sizeof(Payload) - Backfill - Trailer);
-
-    TEST_HRESULT(MpRxEnqueueFrame(GenericMp, &Frame));
-    MpRxFlush(GenericMp);
-
     //
-    // We currently do not support fragments with eBPF, so this packet should
-    // be dropped.
+    // XDP-for-Windows has limited eBPF support for fragments: the first buffer
+    // is visible to eBPF programs, and the remaining fragments (if any) are
+    // inaccessible.
+    //
+    // Actions apply to the entire frame, not just to the first fragement.
     //
+    std::vector<UCHAR> Mask((SIZE_T)Buffers[0].DataLength + Buffers[1].DataLength, 0xFF);
+    MpTxFilter(GenericMp, Payload + Backfill, &Mask[0], (ULONG)Mask.size());
 
-    Sleep(TEST_TIMEOUT_ASYNC_MS);
+    RX_FRAME Frame;
+    RxInitializeFrame(&Frame, If.GetQueueId(), Buffers, RTL_NUMBER_OF(Buffers));
+    TEST_HRESULT(MpRxEnqueueFrame(GenericMp, &Frame));
+    MpRxFlush(GenericMp);
 
-    UINT32 FrameLength = 0;
-    TEST_EQUAL(
-        HRESULT_FROM_WIN32(ERROR_NOT_FOUND),
-        LwfRxGetFrame(FnLwf, If.GetQueueId(), &FrameLength, NULL));
+    MpTxAllocateAndGetFrame(GenericMp, If.GetQueueId());
+    MpTxDequeueFrame(GenericMp, If.GetQueueId());
+    MpTxFlush(GenericMp);
 }
 
 VOID