Ensure EOF is handled propertly during splice.

PiperOrigin-RevId: 304684417

pkg/sentry/kernel/pipe/pipe.go

@@ -255,7 +255,8 @@ func (p *Pipe) write(ctx context.Context, ops writeOps) (int64, error) {
 	// POSIX requires that a write smaller than atomicIOBytes (PIPE_BUF) be
 	// atomic, but requires no atomicity for writes larger than this.
 	wanted := ops.left()
-	if avail := p.max - p.view.Size(); wanted > avail {
+	avail := p.max - p.view.Size()
+	if wanted > avail {
 		if wanted <= p.atomicIOBytes {
 			return 0, syserror.ErrWouldBlock
 		}
@@ -268,8 +269,14 @@ func (p *Pipe) write(ctx context.Context, ops writeOps) (int64, error) {
 		return done, err
 	}
 
-	if wanted > done {
-		// Partial write due to full pipe.
+	if done < avail {
+		// Non-failure, but short write.
+		return done, nil
+	}
+	if done < wanted {
+		// Partial write due to full pipe. Note that this could also be
+		// the short write case above, we would expect a second call
+		// and the write to return zero bytes in this case.
 		return done, syserror.ErrWouldBlock
 	}
 

test/syscalls/linux/sendfile.cc

@@ -530,6 +530,34 @@ TEST(SendFileTest, SendToSpecialFile) {
               SyscallSucceedsWithValue(kSize & (~7)));
 }
 
+TEST(SendFileTest, SendFileToPipe) {
+  // Create temp file.
+  constexpr char kData[] = "<insert-quote-here>";
+  constexpr int kDataSize = sizeof(kData) - 1;
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFileWith(
+      GetAbsoluteTestTmpdir(), kData, TempPath::kDefaultFileMode));
+  const FileDescriptor inf =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_RDONLY));
+
+  // Create a pipe for sending to a pipe.
+  int fds[2];
+  ASSERT_THAT(pipe(fds), SyscallSucceeds());
+  const FileDescriptor rfd(fds[0]);
+  const FileDescriptor wfd(fds[1]);
+
+  // Expect to read up to the given size.
+  std::vector<char> buf(kDataSize);
+  ScopedThread t([&]() {
+    absl::SleepFor(absl::Milliseconds(100));
+    ASSERT_THAT(read(rfd.get(), buf.data(), buf.size()),
+                SyscallSucceedsWithValue(kDataSize));
+  });
+
+  // Send with twice the size of the file, which should hit EOF.
+  EXPECT_THAT(sendfile(wfd.get(), inf.get(), nullptr, kDataSize * 2),
+              SyscallSucceedsWithValue(kDataSize));
+}
+
 }  // namespace
 
 }  // namespace testing