tree b137de61e43c5c17837ba47d27610f9df5c6de6b
parent 1e28eed17697bcf343c6743f0028cc3b5dd88bf0
author Christian Brauner <christian.brauner@ubuntu.com> 1615891937 +0100
committer Christian Brauner <christian.brauner@ubuntu.com> 1616153746 +0100
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cachefiles: do not yet allow on idmapped mounts

Based on discussions (e.g. in [1]) my understanding of cachefiles and
the cachefiles userspace daemon is that it creates a cache on a local
filesystem (e.g. ext4, xfs etc.) for a network filesystem. The way this
is done is by writing "bind" to /dev/cachefiles and pointing it to the
directory to use as the cache.
Currently this directory can technically also be an idmapped mount but
cachefiles aren't yet fully aware of such mounts and thus don't take the
idmapping into account when creating cache entries. This could leave
users confused as the ownership of the files wouldn't match to what they
expressed in the idmapping. Block cache files on idmapped mounts until
the fscache rework is done and we have ported it to support idmapped
mounts.

[1]: https://lore.kernel.org/lkml/20210303161528.n3jzg66ou2wa43qb@wittgenstein
Cc: David Howells <dhowells@redhat.com>
Cc: linux-cachefs@redhat.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
- Christian Brauner <christian.brauner@ubuntu.com>:
  - Ensure that "root" is initialized when cleaning up.

/* v3 */
- David Howells <dhowells@redhat.com>:
  - Reformulate commit message to avoid paragraphs with duplicated
    content.
  - Add a pr_warn() when cachefiles are supposed to be created on
    idmapped mounts.