linux-kernel - [PATCH v2] Update metacopy section in overlayfs documentation

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Message-ID: <20240904165431.13974-1-yuriybelikov1@gmail.com>
Date: Wed,  4 Sep 2024 19:54:29 +0300
From: Yuriy Belikov <yuriybelikov1@...il.com>
To: 
Cc: yuriybelikov1@...il.com,
	Miklos Szeredi <miklos@...redi.hu>,
	Amir Goldstein <amir73il@...il.com>,
	Jonathan Corbet <corbet@....net>,
	linux-unionfs@...r.kernel.org (open list:OVERLAY FILESYSTEM),
	linux-doc@...r.kernel.org (open list:DOCUMENTATION),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2] Update metacopy section in overlayfs documentation

Changes since v1:
- Provide info about trusted.overlay.metacopy extended attribute.
- Minor rephrasing regarding copy-up operation with
  metacopy=on
Signed-off-by: Yuriy Belikov <yuriybelikov1@...il.com>
---
 Documentation/filesystems/overlayfs.rst | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
index 165514401441..e5ad43f4f4d7 100644
--- a/Documentation/filesystems/overlayfs.rst
+++ b/Documentation/filesystems/overlayfs.rst
@@ -367,8 +367,11 @@ Metadata only copy up
 
 When the "metacopy" feature is enabled, overlayfs will only copy
 up metadata (as opposed to whole file), when a metadata specific operation
-like chown/chmod is performed. Full file will be copied up later when
-file is opened for WRITE operation.
+like chown/chmod is performed. An upper file in this state is marked with
+"trusted.overlayfs.metacopy" xattr which indicates that the upper file
+contains no data. Full data will be copied up later when file is opened for
+WRITE operation. After the lower file's data is copied up,
+the "trusted.overlayfs.metacopy" xattr is removed from the upper file.
 
 In other words, this is delayed data copy up operation and data is copied
 up when there is a need to actually modify data.
-- 
2.43.5