[RFC PATCH v1 1/7] fs: Add inode_get_ino() and implement get_ino() for NFS

[Christoph Hellwig]

On Thu, Oct 10, 2024 at 05:26:41PM +0200, Mickaël Salaün wrote:
> When a filesystem manages its own inode numbers, like NFS's fileid shown
> to user space with getattr(), other part of the kernel may still expose
> the private inode->ino through kernel logs and audit.
> 
> Another issue is on 32-bit architectures, on which ino_t is 32 bits,
> whereas the user space's view of an inode number can still be 64 bits.
> 
> Add a new inode_get_ino() helper calling the new struct
> inode_operations' get_ino() when set, to get the user space's view of an
> inode number.  inode_get_ino() is called by generic_fillattr().
> 
> Implement get_ino() for NFS.

The proper interface for that is ->getattr, and you should use that for
all file systems (through the proper vfs wrappers).

And yes, it's really time to move to a 64-bit i_ino, but that's a
separate discussion.