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# SPDX-License-Identifier: GPL-2.0-only
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.rst
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.rst
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
depends on 64BIT
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.rst
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.
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