NODE.JS why we should use : COPYFILE_FICLONE and COPYFILE_FICLONE_FORCE what is it for?

Question

Guys I am trying to learn Node.js by reading Node.js documentation.

I began to learn fs module firstly

and while learning I saw this explanation:

mode is an optional integer that specifies the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE).

at https://nodejs.org/api/fs.html#fscopyfilesrc-dest-mode-callback

I didn't understand what COPYFILE_FICLONE and COPYFILE_FICLONE_FORCE are for, and why we are using these two modes

I researched about "how copy-on-write" works" and found these websites:

and I still didn't understand

may be I thought you guys can help to me and I can understand why is

 //*  Module   *//
let fs = require('fs');

//* Variables *//
source = 'source.txt';
destination = 'hesyy.txt';

//* call back function for error *//
function callback(err) {
    if (!err){
        console.log("source.txt copied to destination");
    } else throw err;
}

// the copy operation will fail if dest already exists.
const {COPYFILE_EXCL} = fs.constants;
// the copy operation will attempt to create a copy-on-write reflink.
// if the platform does not support copy-on-write, then a fallback copy mechanism is used.
const {COPYFILE_FICLONE} = fs.constants;
 // the copy operation will attempt to create a copy-on-write reflink.
 // if the platform does not support copy-on-write, then the operation will fail.
const {COPYFILE_FICLONE_FORCE} = fs.constants;

// fs.copyFile(source,destination,callback);
// fs.copyFile(source,destination,COPYFILE_EXCL,callback);
// fs.copyFile(source,destination,COPYFILE_FICLONE,callback);
fs.copyFile(source,destination,COPYFILE_FICLONE_FORCE,err => {
    if (!err) {
        console.log("Copied");
    }else{
        console.log("err yo:",err);
    }
});

running : node copyFile.js and I got an error by using COPYFILE_FICLONE_FORCE:

err yo: [Error: ENOSYS: function not implemented, copyfile 'C:\Users\CENSORED\Desktop\nodejss\fs\fs.copyFile\source.txt' -> 'C:\Users\CENSORED\Desktop\nodejss\fs\fs.copyFile\hessyy.txt'] {
  errno: -4054,
  code: 'ENOSYS',
  syscall: 'copyfile',
  path: 'C:\\Users\\CENSORED\\Desktop\\nodejss\\fs\\fs.copyFile\\source.txt',
  dest: 'C:\\Users\\CENSORED\\Desktop\\nodejss\\fs\\fs.copyFile\\hessyy.txt'
}

score 0 · Answer 1 · answered Mar 26 '22 at 21:20

According to docs:

mode is an optional integer that specifies the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE).

fs.constants.COPYFILE_EXCL: The copy operation will fail if dest already exists.
fs.constants.COPYFILE_FICLONE: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used.
fs.constants.COPYFILE_FICLONE_FORCE: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail.

So you're using WINDOWS and some flags/functions are not available.

Hi,Jone! sorry for late (i just woke up and i just saw) so you are telling me : these two functions for, if the file name is contain any unusual symbol or flag or function is not available then these two functions using their own font and naming it? "So you're using WINDOWS and some flags/functions are not available." Thanks, Remzi Mete — Remzi Mete, Mar 27 '22 at 11:31

score 0 · Answer 2 · answered Jun 20 '23 at 09:02

What in the link you found that you don't understand?

Copy-on-write or CoW is a technique to efficiently copy data resources in a computer system. If a unit of data is copied but not modified, the "copy" can exist as a reference to the original data. Only when the copied data is modified is a copy created, and new bytes are actually written.

https://www.computerhope.com/jargon/c/copy-on-write.htm

So CoW allows a new object to be copied almost instantly, sharing memory with the old one until the new object is changed. For example copying the existing file A to the new file B that way will make a new B, saying that its current content is the same with A. However when B is modified then B will be actually copied to a separate memory region and the two will not share memory anymore

Copy-on-Write requires filesystem support because you can't mark that a block belongs to multiple files if the FS doesn't allow that. For example on Linux the default ext4 doesn't support CoW at all and you'll have to use a supported FS such as ZFS, Btrfs or XFS. On Windows only ReFS supports CoW, if you use NTFS obviously you'll get the not supported error

[Error: ENOSYS: function not implemented, copyfile 'C:\Users\CENSORED\Desktop\nodejss\fs\fs.copyFile\source.txt' -> 'C:\Users\CENSORED\Desktop\nodejss\fs\fs.copyFile\hessyy.txt'] {

Unfortunately nodejs hasn't been updated to support CoW on Windows yet so even when you use Dev Drive or ReFS you still won't be able to do COPYFILE_FICLONE_FORCE until that's fixed

NODE.JS why we should use : COPYFILE_FICLONE and COPYFILE_FICLONE_FORCE what is it for?

2 Answers2