Let's clarify from where we take idmapping of each type:
- caller
- filesystem
- mount
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Message-Id: <
20230625182047.26854-1-aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
caller's idmapping and then maps that kernel id up according to the
filesystem's idmapping.
+From the implementation point it's worth mentioning how idmappings are represented.
+All idmappings are taken from the corresponding user namespace.
+
+ - caller's idmapping (usually taken from ``current_user_ns()``)
+ - filesystem's idmapping (``sb->s_user_ns``)
+ - mount's idmapping (``mnt_idmap(vfsmnt)``)
+
Let's see some examples with caller/filesystem idmapping but without mount
idmappings. This will exhibit some problems we can hit. After that we will
revisit/reconsider these examples, this time using mount idmappings, to see how