Logic of name_to_handle_at()

Question

I am not getting much information on the new system call name_to_handle_at() and open_to_handle_at(). Can anyone help me out here.

Thanks

An Edit. I just have this

http://comments.gmane.org/gmane.linux.man/2158

Answer 1

These functions are useful for writing user space servers.

For example, when implementing the NFS protocol, which does not have the 'open' concept, or a file descriptor, but instead relies on a persistent file identifier, the name_to_handle_at function can be used to generate this persistent handle in a portable way.

It then gets sent to the client, which will return it back to the server at a later point. The server can then use open_to_handle_at to perform the operation.

One could ask how this is better than simply sending the full path name between client and server. A number of options:

• The file system can use internal (more compact) representations instead of the file name (for example based on inode).
• When going from the handle to file descriptor, potentially less work needs to be done. (no more path traversal)
• In the scenario given above, resource consumption on the server is reduced (no need to keep track of open file descriptors on the server side)