Re: [PATCH 3/6] cachefiles: Use lookup_one() rather than lookup_one_len()

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On Thu, Mar 20, 2025 at 01:49:25PM +0000, David Howells wrote:
> Christian Brauner <brauner@xxxxxxxxxx> wrote:
> 
> > > > It also uses the lookup_one_len() family of functions which implicitly
> > > > use &nop_mnt_idmap.  This mixture of implicit and explicit could be
> > > > confusing.  When we eventually update cachefiles to support idmap mounts
> > > > it
> > > 
> > > Is that something we ever plan to do?
> > 
> > It should be pretty easy to do. I just didn't see a reason to do it yet.
> > 
> > Fwiw, the cache paths that cachefiles uses aren't private mounts like
> > overlayfs does it, i.e., cachefiles doesn't do clone_private_mount() before
> > stashing cache->mnt. ...
> 
> This is probably something cachefilesd needs to do in userspace before telling
> the kernel through /dev/cachefiles where to find the cache.

Afaict, I don't think it matters whether the mount is actually attached
to a mount namespace so cachefilesd could just do:

fd_tree = open_tree(AT_FDCWD, "/path/to/cache", AT_EMPTY_PATH | OPEN_TREE_CLONE);

and use the detached mount for all cachefilesd interactions.




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