Initial QSfera import

Server/vendor/github.com/dgraph-io/ristretto/z/mremap_linux.go

@@ -0,0 +1,57 @@
+//go:build !arm64
+// +build !arm64
+
+/*
+ * Copyright 2020 Dgraph Labs, Inc. and Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package z
+
+import (
+	"fmt"
+	"reflect"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+// mremap is a Linux-specific system call to remap pages in memory. This can be used in place of munmap + mmap.
+func mremap(data []byte, size int) ([]byte, error) {
+	//nolint:lll
+	// taken from <https://github.com/torvalds/linux/blob/f8394f232b1eab649ce2df5c5f15b0e528c92091/include/uapi/linux/mman.h#L8>
+	const MREMAP_MAYMOVE = 0x1
+
+	header := (*reflect.SliceHeader)(unsafe.Pointer(&data))
+	mmapAddr, mmapSize, errno := unix.Syscall6(
+		unix.SYS_MREMAP,
+		header.Data,
+		uintptr(header.Len),
+		uintptr(size),
+		uintptr(MREMAP_MAYMOVE),
+		0,
+		0,
+	)
+	if errno != 0 {
+		return nil, errno
+	}
+	if mmapSize != uintptr(size) {
+		return nil, fmt.Errorf("mremap size mismatch: requested: %d got: %d", size, mmapSize)
+	}
+
+	header.Data = mmapAddr
+	header.Cap = size
+	header.Len = size
+	return data, nil
+}