[SOLVED] What is the usage of open_by_handle_at(2)?

Issue

I learn this system call from docker breakout tech with CAP_DAC_READ_SEARCH.

I am wondering what is this system call originally designed for? Or is there any other typical and common usage of it? Because after a while of searching, I found that the most significant usage of open_by_handle_at(2) is to break out from containers...

Solution

From man open_by_handle:

   These system calls are designed for use by user-space file
   servers.  For example, a user-space NFS server might generate a
   file handle and pass it to an NFS client.  Later, when the client
   wants to open the file, it could pass the handle back to the
   server.  This sort of functionality allows a user-space file
   server to operate in a stateless fashion with respect to the
   files it serves.

Answered By - KamilCuk