v4.19.13 snapshot.
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+config OVERLAY_FS
+ tristate "Overlay filesystem support"
+ select EXPORTFS
+ help
+ An overlay filesystem combines two filesystems - an 'upper' filesystem
+ and a 'lower' filesystem. When a name exists in both filesystems, the
+ object in the 'upper' filesystem is visible while the object in the
+ 'lower' filesystem is either hidden or, in the case of directories,
+ merged with the 'upper' object.
+
+ For more information see Documentation/filesystems/overlayfs.txt
+
+config OVERLAY_FS_REDIRECT_DIR
+ bool "Overlayfs: turn on redirect directory feature by default"
+ depends on OVERLAY_FS
+ help
+ If this config option is enabled then overlay filesystems will use
+ redirects when renaming directories by default. In this case it is
+ still possible to turn off redirects globally with the
+ "redirect_dir=off" module option or on a filesystem instance basis
+ with the "redirect_dir=off" mount option.
+
+ Note, that redirects are not backward compatible. That is, mounting
+ an overlay which has redirects on a kernel that doesn't support this
+ feature will have unexpected results.
+
+ If unsure, say N.
+
+config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW
+ bool "Overlayfs: follow redirects even if redirects are turned off"
+ default y
+ depends on OVERLAY_FS
+ help
+ Disable this to get a possibly more secure configuration, but that
+ might not be backward compatible with previous kernels.
+
+ If backward compatibility is not an issue, then it is safe and
+ recommended to say N here.
+
+ For more information, see Documentation/filesystems/overlayfs.txt
+
+ If unsure, say Y.
+
+config OVERLAY_FS_INDEX
+ bool "Overlayfs: turn on inodes index feature by default"
+ depends on OVERLAY_FS
+ help
+ If this config option is enabled then overlay filesystems will use
+ the index directory to map lower inodes to upper inodes by default.
+ In this case it is still possible to turn off index globally with the
+ "index=off" module option or on a filesystem instance basis with the
+ "index=off" mount option.
+
+ The inodes index feature prevents breaking of lower hardlinks on copy
+ up.
+
+ Note, that the inodes index feature is not backward compatible.
+ That is, mounting an overlay which has an inodes index on a kernel
+ that doesn't support this feature will have unexpected results.
+
+ If unsure, say N.
+
+config OVERLAY_FS_NFS_EXPORT
+ bool "Overlayfs: turn on NFS export feature by default"
+ depends on OVERLAY_FS
+ depends on OVERLAY_FS_INDEX
+ depends on !OVERLAY_FS_METACOPY
+ help
+ If this config option is enabled then overlay filesystems will use
+ the index directory to decode overlay NFS file handles by default.
+ In this case, it is still possible to turn off NFS export support
+ globally with the "nfs_export=off" module option or on a filesystem
+ instance basis with the "nfs_export=off" mount option.
+
+ The NFS export feature creates an index on copy up of every file and
+ directory. This full index is used to detect overlay filesystems
+ inconsistencies on lookup, like redirect from multiple upper dirs to
+ the same lower dir. The full index may incur some overhead on mount
+ time, especially when verifying that directory file handles are not
+ stale.
+
+ Note, that the NFS export feature is not backward compatible.
+ That is, mounting an overlay which has a full index on a kernel
+ that doesn't support this feature will have unexpected results.
+
+ Most users should say N here and enable this feature on a case-by-
+ case basis with the "nfs_export=on" mount option.
+
+ Say N unless you fully understand the consequences.
+
+config OVERLAY_FS_XINO_AUTO
+ bool "Overlayfs: auto enable inode number mapping"
+ default n
+ depends on OVERLAY_FS
+ help
+ If this config option is enabled then overlay filesystems will use
+ unused high bits in undelying filesystem inode numbers to map all
+ inodes to a unified address space. The mapped 64bit inode numbers
+ might not be compatible with applications that expect 32bit inodes.
+
+ If compatibility with applications that expect 32bit inodes is not an
+ issue, then it is safe and recommended to say Y here.
+
+ For more information, see Documentation/filesystems/overlayfs.txt
+
+ If unsure, say N.
+
+config OVERLAY_FS_METACOPY
+ bool "Overlayfs: turn on metadata only copy up feature by default"
+ depends on OVERLAY_FS
+ select OVERLAY_FS_REDIRECT_DIR
+ help
+ If this config option is enabled then overlay filesystems will
+ copy up only metadata where appropriate and data copy up will
+ happen when a file is opened for WRITE operation. It is still
+ possible to turn off this feature globally with the "metacopy=off"
+ module option or on a filesystem instance basis with the
+ "metacopy=off" mount option.
+
+ Note, that this feature is not backward compatible. That is,
+ mounting an overlay which has metacopy only inodes on a kernel
+ that doesn't support this feature will have unexpected results.
+
+ If unsure, say N.