Reverse Lookup for Union-Mounted File System Search Completeness
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Solution Overview
Problem
In union-mounted file systems, searches for files often fail to find files located in subdirectories of lower-order file systems due to the traditional method of maintaining only links to root directories, resulting in incomplete file system searches.
Innovation Solution
Implementing a reverse lookup mechanism that rebuilds the search path from a child directory to a parent directory, allowing the search logic to follow union mount links and perform a second lookup in the corresponding lower-order file system, ensuring that files are correctly located and accessed across multiple union-mounted file systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If only links to root directories are maintained in union-mounted file systems, then device complexity is reduced, but file search completeness deteriorates
Solution Approach 1:
Instead of searching from root directories downward, the patent performs a reverse lookup by traversing from the child directory path upward to identify the corresponding lower-order file system mount point. This inversion of the search direction enables complete file searches across all union-mounted file systems while maintaining a simple mount structure.
2Ease of operation
If traditional forward lookup from root is used, then search logic is simple, but files in lower-order subdirectories are not found
Solution Approach 1:
The patent performs a preliminary reverse lookup to identify the corresponding lower-order file system mount point before conducting the actual file search. This preliminary action ensures that the search logic can access files in lower-order subdirectories by first establishing the correct mount point context.
Data Source
AI summary
In one embodiment, in response to a request for searching a file stored in a first directory, a first lookup is performed by a virtual file system in a first file system to locate the file. The virtual file system traverses from the first directory back to a mount point of the first file system to recreate a search path from the mount point to the first directory. The virtual file system performs a second lookup in a second directory of a second file system that is associated with the mount point to locate the file in the second file system, where second directory is identified by the recreated search path.