Performance Analysis and Optimization of the Hurricane File System ...

CHAPTER 3. HFS ARCHITECTURE 26
current path component, such as /, to extract the subsequent file token of the next path component, such
as /usr/. The caches are accessed as follows (Figure 3.8):
1. The directory contents of the current path component is acquired from the block cache. The directory
contents may occupy several block cache entries and each one is searched until the path name component
is found or until the end of the directory contents is reached.
2. If a directory block is not found in the block cache, the ORS cache is searched for the partial directory
block index. If the ORS cache entry cannot be found, the procedure for ORS cache miss handling is
similar to the previous description of the getAttribute() file system call. The partial directory block
index indicates the disk block of the desired directory block and allows it to be loaded from disk into
the block cache.
3. If the complete directory block index is required, the block cache is searched. If the index cannot be
found, is it loaded from disk and placed into the block cache. The target disk block, which contains the
complete directory block index, is indicated in the very last entry of the partial directory block index.
Once loaded into the block cache, the complete index can be used to load the appropriate directory
content block from disk into the block cache.
The above steps are repeated recursively for each component of the directory path until the path name is
resolved and the final target file token is found. The getDents() file system call, which returns the contents
of a directory rather than the file token of a particular file of directory, interacts with the cache system in a
similar fashion.
The getAttribute() and path name lookup operations cover most of the important code paths and their
traces have demonstrated the role of the meta-data caches and the general operation of HFS.