add a safe getMetadata method to InodeBase

Summary:
Prior to this diff, to read the inode metadata from an InodeBase, you
had to cast it to a FileInode or TreeInode. Add a public getMetadata
call that acquires the appropriate lock depending on whether it's a
FileInode or TreeInode.

Reviewed By: simpkins

Differential Revision: D9327180

fbshipit-source-id: 66594fb639f1ea72a0e48dcb79234e14d87ec4a2

eden/fs/inodes/FileInode.h

@@ -130,7 +130,7 @@ struct FileInodeState {
   size_t openCount{0};
 };
 
-class FileInode : public InodeBaseMetadata<FileInodeState> {
+class FileInode final : public InodeBaseMetadata<FileInodeState> {
  public:
   using Base = InodeBaseMetadata<FileInodeState>;
   using FileHandlePtr = std::shared_ptr<EdenFileHandle>;
@@ -222,7 +222,7 @@ class FileInode : public InodeBaseMetadata<FileInodeState> {
   /**
    * Returns a copy of this inode's metadata.
    */
-  InodeMetadata getMetadata() const;
+  InodeMetadata getMetadata() const override;
 
   /**
    * If this file is backed by a source control Blob, return the hash of the

eden/fs/inodes/InodeBase.cpp

@@ -379,7 +379,7 @@ ParentInodeInfo InodeBase::getParentInfo() const {
   }
 }
 
-InodeMetadata InodeBase::getMetadata() const {
+InodeMetadata InodeBase::getMetadataLocked() const {
   return getMount()->getInodeMetadataTable()->getOrThrow(getNodeId());
 }
 

eden/fs/inodes/InodeBase.h

@@ -358,6 +358,11 @@ class InodeBase {
     return *loc;
   }
 
+  /**
+   * Acquire this inode's contents lock and return its metadata.
+   */
+  virtual InodeMetadata getMetadata() const = 0;
+
  protected:
   /**
    * Returns current time from EdenMount's clock.
@@ -375,8 +380,9 @@ class InodeBase {
   void updateJournal();
 
  private:
-  // Private so only InodeBaseMetadata can call them
-  InodeMetadata getMetadata() const;
+  // The caller (which is always InodeBaseMetadata) must be holding the inode
+  // state lock for this type of inode when calling getMetadataLocked().
+  InodeMetadata getMetadataLocked() const;
   void updateAtime();
   InodeTimestamps updateMtimeAndCtime(timespec now);
 
@@ -570,7 +576,7 @@ class InodeBaseMetadata : public InodeBase {
    * Get this inode's metadata. The inode's state lock must be held.
    */
   InodeMetadata getMetadataLocked(const InodeState&) const {
-    return InodeBase::getMetadata();
+    return InodeBase::getMetadataLocked();
   }
 
   /**

eden/fs/inodes/TreeInode.h

@@ -66,7 +66,7 @@ struct TreeInodeState {
 /**
  * Represents a directory in the file system.
  */
-class TreeInode : public InodeBaseMetadata<DirContents> {
+class TreeInode final : public InodeBaseMetadata<DirContents> {
  public:
   using Base = InodeBaseMetadata<DirContents>;
 
@@ -397,7 +397,7 @@ class TreeInode : public InodeBaseMetadata<DirContents> {
   /**
    * Returns a copy of this inode's metadata.
    */
-  InodeMetadata getMetadata() const;
+  InodeMetadata getMetadata() const override;
 
   /**
    * Updates the last-access timestamp.  Public so TreeInodeDirHandle can call