Dentry

In computing, a dentry (directory entry) is a kernel-level object used by the virtual file system (VFS) to represent a component of a pathname and to accelerate pathname resolution. The dentry is an in-memory abstraction that links names within directories to the underlying filesystem inode structures and provides a cache layer (the dcache) for repeated lookups.

A dentry typically contains a name, pointers to its parent and children, a reference to an inode when the name corresponds to an existing object, and metadata such as reference counts and flags. Negative dentries represent names that were looked up but do not exist; they are retained temporarily to avoid repeated failed lookups. Dentries are created during lookup operations and managed with reference counting functions; when they are no longer referenced they may be reclaimed by the cache.

Dentries support filesystem-independent operations such as lookup, revalidation and instantiation. They interact closely with inodes but are ephemeral: inode objects describe persistent filesystem entities, whereas dentries describe namespace relationships and are rebuilt as needed. The dcache improves performance by reducing expensive filesystem or disk accesses, but it introduces complexity in cache coherency, locking and lifecycle management. Implementations in Unix-like kernels use dentries as a core component of pathname resolution and namespace handling.