bastion 0.53.2

client-go/diskmap_windows.go

@@ -0,0 +1,98 @@
+package main
+
+// The two platform questions the disk map asks, answered for Windows.
+
+import (
+	"fmt"
+	"io/fs"
+
+	"golang.org/x/sys/windows"
+)
+
+// dmDeviceOf on Windows says "no device information", and that is the correct
+// answer rather than a stub.
+//
+// FileInfo.Sys() here is a *syscall.Win32FileAttributeData, which carries
+// attributes and timestamps and NO volume identity — the field a caller would
+// want (dwVolumeSerialNumber) only comes from GetFileInformationByHandle,
+// which needs an OPEN HANDLE on the file. Opening every directory to ask what
+// volume it is on is exactly the syscall this unit is not allowed to make, and
+// paying it 87,000 times would also be the slowest thing in the walk.
+//
+// Nothing is lost by saying no, because on Windows the drive letter IS the
+// boundary: a walk rooted at C:\ cannot reach D: except through a junction or
+// a symlink, and filepath.WalkDir does not follow either (fs.DirEntry is
+// lstat-shaped, so a reparse point has IsDir() == false and is never
+// descended). The mount-crossing defence unix gets from st_dev, Windows gets
+// from not following links — which it has for free and unconditionally.
+//
+// UNVERIFIED: nothing here has been run on Windows. Cross-compiled and vetted
+// for all three Windows targets, code-reviewed on Linux.
+func dmDeviceOf(path string) (uint64, bool) { return 0, false }
+
+func dmDeviceOfInfo(fi fs.FileInfo) (uint64, bool) { return 0, false }
+
+// dmVolumeRoots is the machine's FIXED drives, and only the fixed ones.
+//
+// GetLogicalDrives returns a bitmask of present letters — bit 0 is A:, bit 25
+// is Z: — and GetDriveType says what each one is. Both are in
+// golang.org/x/sys/windows, which this binary already depends on (go.mod), so
+// this costs no new module and no cgo: the whole point of deploy/publish.sh is
+// six targets out of one CGO_ENABLED=0 container.
+//
+// WHY ONLY DRIVE_FIXED, with the others named on the page rather than silently
+// dropped:
+//
+//   - DRIVE_REMOTE is a network share. Walking it sends every directory read
+//     over the wire, and on a VPN that is down each one waits for a timeout;
+//     a "map my disk" click would appear to hang for minutes and the bytes it
+//     eventually counted would not be on this machine at all.
+//   - DRIVE_CDROM and DRIVE_REMOVABLE spin up hardware to answer, and an empty
+//     drive answers with an error dialog on some configurations.
+//   - DRIVE_RAMDISK is memory, not disk, and would be counted as space that
+//     could be freed when there is nothing there to free.
+//
+// WinDirStat opens with "select the drives to scan" for precisely this reason.
+// This picks the same default it does and SAYS what it left out, because a map
+// that quietly omits a drive is worse than one that names it.
+func dmVolumeRoots() (roots []string, notes []string) {
+	mask, err := windows.GetLogicalDrives()
+	if err != nil || mask == 0 {
+		// No answer from the OS is not "no drives". Fall back to the system
+		// drive, which is the one that always exists, and say the enumeration
+		// failed so a missing D: reads as a known gap rather than as fact.
+		notes = append(notes, "this machine's drive list could not be read from Windows, so the map covers C: only")
+		return []string{`C:\`}, notes
+	}
+	var skipped []string
+	for bit := uint(0); bit < 26; bit++ {
+		if mask&(1<<bit) == 0 {
+			continue
+		}
+		root := fmt.Sprintf("%c:\\", 'A'+rune(bit))
+		p, perr := windows.UTF16PtrFromString(root)
+		if perr != nil {
+			continue
+		}
+		switch windows.GetDriveType(p) {
+		case windows.DRIVE_FIXED:
+			roots = append(roots, root)
+		case windows.DRIVE_REMOTE:
+			skipped = append(skipped, root+" (a network drive — its files are not on this machine)")
+		case windows.DRIVE_CDROM:
+			skipped = append(skipped, root+" (a disc drive)")
+		case windows.DRIVE_REMOVABLE:
+			skipped = append(skipped, root+" (a removable drive)")
+		case windows.DRIVE_RAMDISK:
+			skipped = append(skipped, root+" (a RAM disk — it holds no disk space)")
+		}
+	}
+	if len(roots) == 0 {
+		notes = append(notes, "Windows reported no fixed drive on this machine, so the map covers C: only")
+		roots = []string{`C:\`}
+	}
+	for _, s := range skipped {
+		notes = append(notes, "not mapped: "+s)
+	}
+	return roots, notes
+}