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-rw-r--r--Documentation/filesystems/idmappings.rst7
1 files changed, 7 insertions, 0 deletions
diff --git a/Documentation/filesystems/idmappings.rst b/Documentation/filesystems/idmappings.rst
index ad6d21640576..f3d168c9f0b9 100644
--- a/Documentation/filesystems/idmappings.rst
+++ b/Documentation/filesystems/idmappings.rst
@@ -373,6 +373,13 @@ kernel maps the caller's userspace id down into a kernel id according to the
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