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