Feature request: allow app developer to determine if UnifyFS filesystem is mounted

System information

Affects all systems.

Describe the problem you're observing

UnifyFS can be compiled with or without support for automatically mounting the filesystem during the MPI_Init() call. However, once UnifyFS is built, there is no way to know if this feature is present. As such, an application developer who didn't personally build UnifyFS doesn't know whether or not to call unifyfs_mount().

Right now, unifyfs_mount() simply returns a generic failure code if it's called when the filesystem has already been mounted. A possible solution to this issue would be to change unifyfs_mount() to return a specific error code indicating that the filesystem is already mounted. Application developers could then call unifyfs_mount() and know that if they receive that error code, they don't need to abort their programs.

Start by reviewing the unifyfs_mount() API and the automatic mounting behavior during MPI_Init(), then trace how the current generic failure is reported when the filesystem is already mounted. Done means an application can distinguish that condition and decide whether it needs to abort, with coverage for both mount scenarios.