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overlayfs.rst: update metacopy section in overlayfs documentation

- Provide info about trusted.overlay.metacopy extended attribute
- Minor rephrasing regarding copy-up operation with metacopy=on

Signed-off-by: Yuriy Belikov <yuriybelikov1@gmail.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
This commit is contained in:
Yuriy Belikov 2024-09-04 19:54:29 +03:00 committed by Amir Goldstein
parent 7d6899fb69
commit 930b7c32ea

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@ -367,8 +367,11 @@ Metadata only copy up
When the "metacopy" feature is enabled, overlayfs will only copy When the "metacopy" feature is enabled, overlayfs will only copy
up metadata (as opposed to whole file), when a metadata specific operation 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 like chown/chmod is performed. An upper file in this state is marked with
file is opened for WRITE operation. "trusted.overlayfs.metacopy" xattr which indicates that the upper file
contains no data. The 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 In other words, this is delayed data copy up operation and data is copied
up when there is a need to actually modify data. up when there is a need to actually modify data.