1 files changed, 87 insertions, 2 deletions

diff --git a/src/inode2filename/inode.h b/src/inode2filename/inode.h
index 2dd5611..f336a14 100644
--- a/src/inode2filename/inode.h
+++ b/src/inode2filename/inode.h
@@ -23,22 +23,97 @@
 
 namespace iorap::inode2filename {
 
+// Avoid polluting headers.
+#if defined(__ANDROID__)
+#  if !defined(__LP64__)
+/* This historical accident means that we had a 32-bit dev_t on 32-bit architectures. */
+using dev_t = uint32_t;
+#  else
+using dev_t = uint64_t;
+#  endif
+using ino_t = unsigned long;
+#else
+#  if !defined(__x86_64__)
+using dev_t = unsigned long long;
+using ino_t = unsigned long long;
+#  else
+using dev_t = unsigned long;
+using ino_t = unsigned long;
+#  endif
+#endif
+
+#ifdef makedev
+#undef makedev
+#endif
+
+/** Combines `major` and `minor` into a device number. */
+constexpr inline dev_t makedev(unsigned int major, unsigned int minor) {
+  return
+      (((major) & 0xfffff000ULL) << 32) | (((major) & 0xfffULL) << 8) |
+      (((minor) & 0xffffff00ULL) << 12) | (((minor) & 0xffULL));
+}
+
+#ifdef major
+#undef major
+#endif
+
+/** Extracts the major part of a device number. */
+constexpr inline unsigned int major(dev_t dev) {
+  return
+      ((unsigned) ((((unsigned long long) (dev) >> 32) & 0xfffff000) | (((dev) >> 8) & 0xfff)));
+}
+
+#ifdef minor
+#undef minor
+#endif
+
+/** Extracts the minor part of a device number. */
+constexpr inline unsigned int minor(dev_t dev) {
+  return
+      ((unsigned) ((((dev) >> 12) & 0xffffff00) | ((dev) & 0xff)));
+};
+// Note: above definitions copied from sysmacros.h, to avoid polluting global namespace in a header.
+
+/*
+ * A convenient datum representing a (dev_t, ino_t) tuple.
+ *
+ * ino_t values may be reused across different devices (e.g. different partitions),
+ * so we need the full tuple to uniquely identify an inode on a system.
+ */
 struct Inode {
   size_t device_major;  // dev_t = makedev(major, minor)
   size_t device_minor;
   size_t inode;         // ino_t = inode
 
+  // "Major:minor:inode" OR "dev_t@inode"
   static bool Parse(const std::string& str, /*out*/Inode* out, /*out*/std::string* error_msg);
 
-  bool operator==(const Inode& rhs) const {
+  constexpr bool operator==(const Inode& rhs) const {
     return device_major == rhs.device_major &&
         device_minor == rhs.device_minor &&
         inode == rhs.inode;
   }
 
-  bool operator!=(const Inode& rhs) const {
+  constexpr bool operator!=(const Inode& rhs) const {
     return !(*this == rhs);
   }
+
+  Inode() = default;
+  constexpr Inode(size_t device_major, size_t device_minor, size_t inode)
+    : device_major{device_major}, device_minor{device_minor}, inode{inode} {
+  }
+
+  static constexpr Inode FromDeviceAndInode(dev_t dev, ino_t inode) {
+    return Inode{major(dev), minor(dev), static_cast<size_t>(inode)};
+  }
+
+  constexpr dev_t GetDevice() const {
+    return makedev(device_major, device_minor);
+  }
+
+  constexpr ino_t GetInode() const {
+    return static_cast<ino_t>(inode);
+  }
 };
 
 inline std::ostream& operator<<(std::ostream& os, const Inode& inode) {
@@ -62,4 +137,14 @@ namespace std {
   };
 }  // namespace std
 
+namespace rxcpp {
+template <class T, typename>
+struct filtered_hash;
+
+// support for the 'distinct' rx operator.
+template <>
+struct filtered_hash<iorap::inode2filename::Inode, void> : std::hash<iorap::inode2filename::Inode> {
+};
+}  // namespace rxcpp
+
 #endif  // IORAP_SRC_INODE2FILENAME_INODE_H_