Show something mumble mumble APFS cloned files mumble?

Uncloned.swift

import Cocoa

// https://cocoa-dev.apple.narkive.com/Ciy40e20/is-cloning-the-same-as-copying-in-apfs#post8
func unclonedSize(of url: URL) throws -> off_t {
    var list = attrlist(bitmapcount: UInt16(ATTR_BIT_MAP_COUNT),
                        reserved: 0,
                        commonattr: 0,
                        volattr: 0,
                        dirattr: 0,
                        fileattr: 0,
                        forkattr: attrgroup_t(ATTR_CMNEXT_PRIVATESIZE))
    
    let bufsize = 4 + MemoryLayout<off_t>.size
    let buf = UnsafeMutablePointer<UInt8>.allocate(capacity: bufsize)
    defer { buf.deallocate() }
    let err = url.withUnsafeFileSystemRepresentation { getattrlist($0, &list, buf, bufsize, UInt32(FSOPT_ATTR_CMN_EXTENDED)) }
    if err != 0 { throw POSIXError.Code(rawValue: errno).map { POSIXError($0) } ?? CocoaError(.fileReadUnknown) }
    let attrsize = buf.withMemoryRebound(to: UInt32.self, capacity: 1) { $0.pointee }
    if attrsize < bufsize { throw CocoaError(.fileReadUnknown) }
    var unclonedSize: off_t = 0
    _ = withUnsafeMutableBytes(of: &unclonedSize) { memcpy($0.baseAddress!, buf + 4, MemoryLayout<off_t>.size) }
    return unclonedSize
}

do {
    let regular = URL(fileURLWithPath: "/Users/andre/borkens/regular.dmg")
    let clone = URL(fileURLWithPath: "/Users/andre/borkens/clone.dmg")
    let cpRegular = URL(fileURLWithPath: "/Users/andre/borkens/cp-regular.dmg")
    let cloneAppended = URL(fileURLWithPath: "/Users/andre/borkens/clone-appended.dmg")

    print("Uncloned size of regular.dmg      : \(try unclonedSize(of: regular))")
    print("Uncloned size of clone.dmg        : \(try unclonedSize(of: clone))")
    print("Uncloned size of cpRegular.dmg    : \(try unclonedSize(of: cpRegular))")
    print("Uncloned size of cloneAppended.dmg: \(try unclonedSize(of: cloneAppended))")

} catch {
    print("Error occurred: \(error.localizedDescription)")
}

Let's try it. In Xcode, make a new macOS playground and use the above Swift code. The test files are described as follows:

• regular.dmg is a file of zeroes made with dd
• cp-regular.dmg is a copy of that file made with cp, no arguments. standard copy.
• clone.dmg was made with clonefile (cp -c).
• clone-appended.dmg is a clone of regular.dmg, but with 10 bytes appended to it with echo and >>.

xomg% /bin/ls -le@ *.dmg
-rw-r--r--  1 andre  staff  104857610 Apr 30 21:35 clone-appended.dmg
-rw-r--r--  1 andre  staff  104857600 Apr 30 21:32 clone.dmg
-rw-r--r--  1 andre  staff  104857600 Apr 30 21:32 cp-regular.dmg
-rw-r--r--  1 andre  staff  104857600 Apr 30 21:32 regular.dmg

The playground output is:

Uncloned size of regular.dmg      : 0
Uncloned size of clone.dmg        : 0
Uncloned size of cpRegular.dmg    : 104857600
Uncloned size of cloneAppended.dmg: 14921728

Because this is a gist, conclusions are left as an exercise for the reader. I'll even tell you where the answer is: in the man page for getattrlist(2).