Initial QSfera import

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

@@ -0,0 +1,71 @@
+/*
+ * 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 (
+	"os"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+// mmap uses the mmap system call to memory-map a file. If writable is true,
+// memory protection of the pages is set so that they may be written to as well.
+func mmap(fd *os.File, writable bool, size int64) ([]byte, error) {
+	mtype := unix.PROT_READ
+	if writable {
+		mtype |= unix.PROT_WRITE
+	}
+	return unix.Mmap(int(fd.Fd()), 0, int(size), mtype, unix.MAP_SHARED)
+}
+
+// munmap unmaps a previously mapped slice.
+//
+// unix.Munmap maintains an internal list of mmapped addresses, and only calls munmap
+// if the address is present in that list. If we use mremap, this list is not updated.
+// To bypass this, we call munmap ourselves.
+func munmap(data []byte) error {
+	if len(data) == 0 || len(data) != cap(data) {
+		return unix.EINVAL
+	}
+	_, _, errno := unix.Syscall(
+		unix.SYS_MUNMAP,
+		uintptr(unsafe.Pointer(&data[0])),
+		uintptr(len(data)),
+		0,
+	)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
+
+// madvise uses the madvise system call to give advise about the use of memory
+// when using a slice that is memory-mapped to a file. Set the readahead flag to
+// false if page references are expected in random order.
+func madvise(b []byte, readahead bool) error {
+	flags := unix.MADV_NORMAL
+	if !readahead {
+		flags = unix.MADV_RANDOM
+	}
+	return unix.Madvise(b, flags)
+}
+
+// msync writes any modified data to persistent storage.
+func msync(b []byte) error {
+	return unix.Msync(b, unix.MS_SYNC)
+}