Shared Memory File System

This supports the POSIX shm_open() APIs for shared memory among unrelated apps.

It can be enabled with CONFIG_FS_SHMFS=y. To check how it works, please also enable the example app via CONFIG_EXMAPLE_SHM=y and run shm_test from NSH command line.

This file system doesn't support mount operations though.

If comment the line using shm_unlink() in the example app, we can see a file under /var/shm/ from NSH command line after running the example. We can also remove that file from command line.