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| 1 | +package mountinfo |
| 2 | + |
| 3 | +import ( |
| 4 | + "os" |
| 5 | + "path/filepath" |
| 6 | + |
| 7 | + "golang.org/x/sys/unix" |
| 8 | +) |
| 9 | + |
| 10 | +// mountedByOpenat2 is a method of detecting a mount that works for all kinds |
| 11 | +// of mounts (incl. bind mounts), but requires a recent (v5.6+) linux kernel. |
| 12 | +func mountedByOpenat2(path string) (bool, error) { |
| 13 | + dir, last := filepath.Split(path) |
| 14 | + |
| 15 | + dirfd, err := unix.Openat2(unix.AT_FDCWD, dir, &unix.OpenHow{ |
| 16 | + Flags: unix.O_PATH | unix.O_CLOEXEC, |
| 17 | + }) |
| 18 | + if err != nil { |
| 19 | + if err == unix.ENOENT { // not a mount |
| 20 | + return false, nil |
| 21 | + } |
| 22 | + return false, &os.PathError{Op: "openat2", Path: dir, Err: err} |
| 23 | + } |
| 24 | + fd, err := unix.Openat2(dirfd, last, &unix.OpenHow{ |
| 25 | + Flags: unix.O_PATH | unix.O_CLOEXEC | unix.O_NOFOLLOW, |
| 26 | + Resolve: unix.RESOLVE_NO_XDEV, |
| 27 | + }) |
| 28 | + _ = unix.Close(dirfd) |
| 29 | + switch err { |
| 30 | + case nil: // definitely not a mount |
| 31 | + _ = unix.Close(fd) |
| 32 | + return false, nil |
| 33 | + case unix.EXDEV: // definitely a mount |
| 34 | + return true, nil |
| 35 | + case unix.ENOENT: // not a mount |
| 36 | + return false, nil |
| 37 | + } |
| 38 | + // not sure |
| 39 | + return false, &os.PathError{Op: "openat2", Path: path, Err: err} |
| 40 | +} |
| 41 | + |
| 42 | +func mounted(path string) (bool, error) { |
| 43 | + // Try a fast path, using openat2() with RESOLVE_NO_XDEV. |
| 44 | + mounted, err := mountedByOpenat2(path) |
| 45 | + if err == nil { |
| 46 | + return mounted, nil |
| 47 | + } |
| 48 | + // Another fast path: compare st.st_dev fields. |
| 49 | + mounted, err = mountedByStat(path) |
| 50 | + // This does not work for bind mounts, so false negative |
| 51 | + // is possible, therefore only trust if return is true. |
| 52 | + if mounted && err == nil { |
| 53 | + return mounted, nil |
| 54 | + } |
| 55 | + |
| 56 | + // Fallback to parsing mountinfo |
| 57 | + return mountedByMountinfo(path) |
| 58 | +} |
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