github.com/zuoyebang/bitalostable@v1.0.1-0.20240229032404-e3b99a834294/vfs/fd.go (about)

     1  // Copyright 2021 The LevelDB-Go and Pebble Authors. All rights reserved. Use
     2  // of this source code is governed by a BSD-style license that can be found in
     3  // the LICENSE file.
     4  
     5  package vfs
     6  
     7  // fdGetter is an interface for a file with an Fd() method. A lot of
     8  // File related optimizations (eg. Prefetch(), WAL recycling) rely on the
     9  // existence of the Fd method to return a raw file descriptor.
    10  type fdGetter interface {
    11  	Fd() uintptr
    12  }
    13  
    14  // fdFileWrapper is a File wrapper that also exposes an Fd() method. Used to
    15  // wrap outer (wrapped) Files that could unintentionally hide the Fd() method
    16  // exposed by the inner (unwrapped) File. It effectively lets the Fd() method
    17  // bypass the outer File and go to the inner File.
    18  type fdFileWrapper struct {
    19  	File
    20  
    21  	// All methods usually pass through to File above, except for Fd(), which
    22  	// bypasses it and gets called directly on the inner file.
    23  	inner fdGetter
    24  }
    25  
    26  func (f *fdFileWrapper) Fd() uintptr {
    27  	return f.inner.Fd()
    28  }
    29  
    30  // WithFd takes an inner (unwrapped) and an outer (wrapped) vfs.File,
    31  // and returns an fdFileWrapper if the inner file has an Fd() method. Use this
    32  // method to fix the hiding of the Fd() method and the subsequent unintentional
    33  // disabling of Fd-related file optimizations.
    34  func WithFd(inner, outer File) File {
    35  	if f, ok := inner.(fdGetter); ok {
    36  		return &fdFileWrapper{
    37  			File:  outer,
    38  			inner: f,
    39  		}
    40  	}
    41  	return outer
    42  }