Blockdependsfs

Blockdependsfs is a FUSE (Filesystem in Userspace) module for Linux that allows a filesystem to depend on the state of other filesystems. Specifically, it can be configured to only be mountable if certain other filesystems are already mounted and in a specific state. This is achieved by creating a mount point for blockdependsfs that will only become active when the specified dependencies are met.

The primary use case for blockdependsfs is to ensure that critical filesystems are available before attempting to mount other filesystems that rely on them. For example, a user might configure blockdependsfs to mount a configuration directory only after the root filesystem has been successfully mounted. This prevents potential errors or system instability that could arise from trying to access data on a filesystem that is not yet accessible.

Configuration of blockdependsfs typically involves a configuration file that lists the dependencies. These dependencies can include the mount status and specific device nodes of other filesystems. When the blockdependsfs mount point is accessed, it checks these conditions. If the dependencies are not met, the access will fail. If the dependencies are met, the underlying filesystem specified in the configuration will be accessed. This provides a robust mechanism for managing filesystem mounting order and ensuring data integrity.