Initial commit

Proof-of-concept implementation. Bugs will occur.

vendor/github.com/hanwen/go-fuse/v2/fuse/passthrough_linux.go

@@ -0,0 +1,46 @@
+// Copyright 2024 the Go-FUSE Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fuse
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+const (
+	_DEV_IOC_BACKING_OPEN  = 0x4010e501
+	_DEV_IOC_BACKING_CLOSE = 0x4004e502
+)
+
+// RegisterBackingFd registers the given file descriptor in the
+// kernel, so the kernel can bypass FUSE and access the backing file
+// directly for read and write calls. On success a backing ID is
+// returned. The backing ID should unregistered using
+// UnregisterBackingFd() once the file is released.  Within the
+// kernel, an inode can only have a single backing file, so multiple
+// Open/Create calls should coordinate to return a consistent backing
+// ID.
+func (ms *Server) RegisterBackingFd(m *BackingMap) (int32, syscall.Errno) {
+	ms.writeMu.Lock()
+	id, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(ms.mountFd), uintptr(_DEV_IOC_BACKING_OPEN), uintptr(unsafe.Pointer(m)))
+	ms.writeMu.Unlock()
+	if ms.opts.Debug {
+		ms.opts.Logger.Printf("ioctl: BACKING_OPEN %v: id %d (%v)", m.string(), id, errno)
+	}
+	return int32(id), errno
+}
+
+// UnregisterBackingFd unregisters the given ID in the kernel. The ID
+// should have been acquired before using RegisterBackingFd.
+func (ms *Server) UnregisterBackingFd(id int32) syscall.Errno {
+	ms.writeMu.Lock()
+	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(ms.mountFd), uintptr(_DEV_IOC_BACKING_CLOSE), uintptr(unsafe.Pointer(&id)))
+	ms.writeMu.Unlock()
+
+	if ms.opts.Debug {
+		ms.opts.Logger.Printf("ioctl: BACKING_CLOSE id %d: %v", id, errno)
+	}
+	return errno
+}