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Message-Id: <20230625182047.26854-1-aleksandr.mikhalitsyn@canonical.com>
Date: Sun, 25 Jun 2023 20:20:47 +0200
From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To: brauner@...nel.org
Cc: linux-fsdevel@...r.kernel.org,
Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>,
Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
Seth Forshee <sforshee@...nel.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH v2] docs: filesystems: idmappings: clarify from where idmappings are taken
Let's clarify from where we take idmapping of each type:
- caller
- filesystem
- mount
Cc: Jonathan Corbet <corbet@....net>
Cc: Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-doc@...r.kernel.org
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
---
v2:
- fixed https://lore.kernel.org/oe-kbuild-all/202306252253.qxHG1txo-lkp@intel.com/
---
Documentation/filesystems/idmappings.rst | 7 +++++++
1 file changed, 7 insertions(+)
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
--
2.34.1
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