# SPDX-License-Identifier: GPL-2.0-only
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config OVERLAY_FS
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tristate "Overlay filesystem support"
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select EXPORTFS
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help
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An overlay filesystem combines two filesystems - an 'upper' filesystem
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and a 'lower' filesystem. When a name exists in both filesystems, the
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object in the 'upper' filesystem is visible while the object in the
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'lower' filesystem is either hidden or, in the case of directories,
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merged with the 'upper' object.
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For more information see Documentation/filesystems/overlayfs.rst
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config OVERLAY_FS_REDIRECT_DIR
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bool "Overlayfs: turn on redirect directory feature by default"
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depends on OVERLAY_FS
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help
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If this config option is enabled then overlay filesystems will use
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redirects when renaming directories by default. In this case it is
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still possible to turn off redirects globally with the
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"redirect_dir=off" module option or on a filesystem instance basis
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with the "redirect_dir=off" mount option.
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Note, that redirects are not backward compatible. That is, mounting
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an overlay which has redirects on a kernel that doesn't support this
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feature will have unexpected results.
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If unsure, say N.
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config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW
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bool "Overlayfs: follow redirects even if redirects are turned off"
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default y
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depends on OVERLAY_FS
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help
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Disable this to get a possibly more secure configuration, but that
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might not be backward compatible with previous kernels.
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If backward compatibility is not an issue, then it is safe and
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recommended to say N here.
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For more information, see Documentation/filesystems/overlayfs.rst
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If unsure, say Y.
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config OVERLAY_FS_INDEX
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bool "Overlayfs: turn on inodes index feature by default"
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depends on OVERLAY_FS
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help
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If this config option is enabled then overlay filesystems will use
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the index directory to map lower inodes to upper inodes by default.
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In this case it is still possible to turn off index globally with the
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"index=off" module option or on a filesystem instance basis with the
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"index=off" mount option.
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The inodes index feature prevents breaking of lower hardlinks on copy
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up.
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Note, that the inodes index feature is not backward compatible.
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That is, mounting an overlay which has an inodes index on a kernel
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that doesn't support this feature will have unexpected results.
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If unsure, say N.
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config OVERLAY_FS_NFS_EXPORT
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bool "Overlayfs: turn on NFS export feature by default"
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depends on OVERLAY_FS
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depends on OVERLAY_FS_INDEX
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depends on !OVERLAY_FS_METACOPY
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help
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If this config option is enabled then overlay filesystems will use
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the index directory to decode overlay NFS file handles by default.
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In this case, it is still possible to turn off NFS export support
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globally with the "nfs_export=off" module option or on a filesystem
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instance basis with the "nfs_export=off" mount option.
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The NFS export feature creates an index on copy up of every file and
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directory. This full index is used to detect overlay filesystems
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inconsistencies on lookup, like redirect from multiple upper dirs to
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the same lower dir. The full index may incur some overhead on mount
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time, especially when verifying that directory file handles are not
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stale.
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Note, that the NFS export feature is not backward compatible.
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That is, mounting an overlay which has a full index on a kernel
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that doesn't support this feature will have unexpected results.
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Most users should say N here and enable this feature on a case-by-
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case basis with the "nfs_export=on" mount option.
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Say N unless you fully understand the consequences.
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config OVERLAY_FS_XINO_AUTO
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bool "Overlayfs: auto enable inode number mapping"
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default n
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depends on OVERLAY_FS
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depends on 64BIT
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help
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If this config option is enabled then overlay filesystems will use
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unused high bits in undelying filesystem inode numbers to map all
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inodes to a unified address space. The mapped 64bit inode numbers
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might not be compatible with applications that expect 32bit inodes.
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If compatibility with applications that expect 32bit inodes is not an
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issue, then it is safe and recommended to say Y here.
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For more information, see Documentation/filesystems/overlayfs.rst
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If unsure, say N.
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config OVERLAY_FS_METACOPY
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bool "Overlayfs: turn on metadata only copy up feature by default"
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depends on OVERLAY_FS
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select OVERLAY_FS_REDIRECT_DIR
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help
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If this config option is enabled then overlay filesystems will
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copy up only metadata where appropriate and data copy up will
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happen when a file is opened for WRITE operation. It is still
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possible to turn off this feature globally with the "metacopy=off"
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module option or on a filesystem instance basis with the
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"metacopy=off" mount option.
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Note, that this feature is not backward compatible. That is,
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mounting an overlay which has metacopy only inodes on a kernel
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that doesn't support this feature will have unexpected results.
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If unsure, say N.
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