summaryrefslogtreecommitdiff
path: root/Documentation/filesystems
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r--Documentation/filesystems/idmappings.rst14
1 files changed, 11 insertions, 3 deletions
diff --git a/Documentation/filesystems/idmappings.rst b/Documentation/filesystems/idmappings.rst
index ad6d21640576..d095c5838f94 100644
--- a/Documentation/filesystems/idmappings.rst
+++ b/Documentation/filesystems/idmappings.rst
@@ -146,9 +146,10 @@ For the rest of this document we will prefix all userspace ids with ``u`` and
all kernel ids with ``k``. Ranges of idmappings will be prefixed with ``r``. So
an idmapping will be written as ``u0:k10000:r10000``.
-For example, the id ``u1000`` is an id in the upper idmapset or "userspace
-idmapset" starting with ``u1000``. And it is mapped to ``k11000`` which is a
-kernel id in the lower idmapset or "kernel idmapset" starting with ``k10000``.
+For example, within this idmapping, the id ``u1000`` is an id in the upper
+idmapset or "userspace idmapset" starting with ``u0``. And it is mapped to
+``k11000`` which is a kernel id in the lower idmapset or "kernel idmapset"
+starting with ``k10000``.
A kernel id is always created by an idmapping. Such idmappings are associated
with user namespaces. Since we mainly care about how idmappings work we're not
@@ -373,6 +374,13 @@ 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