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TOMOYO Linux Cross Reference
Linux/fs/overlayfs/Kconfig

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  1 # SPDX-License-Identifier: GPL-2.0-only
  2 config OVERLAY_FS
  3         tristate "Overlay filesystem support"
  4         select FS_STACK
  5         select EXPORTFS
  6         help
  7           An overlay filesystem combines two filesystems - an 'upper' filesystem
  8           and a 'lower' filesystem.  When a name exists in both filesystems, the
  9           object in the 'upper' filesystem is visible while the object in the
 10           'lower' filesystem is either hidden or, in the case of directories,
 11           merged with the 'upper' object.
 12 
 13           For more information see Documentation/filesystems/overlayfs.rst
 14 
 15 config OVERLAY_FS_REDIRECT_DIR
 16         bool "Overlayfs: turn on redirect directory feature by default"
 17         depends on OVERLAY_FS
 18         help
 19           If this config option is enabled then overlay filesystems will use
 20           redirects when renaming directories by default.  In this case it is
 21           still possible to turn off redirects globally with the
 22           "redirect_dir=off" module option or on a filesystem instance basis
 23           with the "redirect_dir=off" mount option.
 24 
 25           Note, that redirects are not backward compatible.  That is, mounting
 26           an overlay which has redirects on a kernel that doesn't support this
 27           feature will have unexpected results.
 28 
 29           If unsure, say N.
 30 
 31 config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW
 32         bool "Overlayfs: follow redirects even if redirects are turned off"
 33         default y
 34         depends on OVERLAY_FS
 35         help
 36           Disable this to get a possibly more secure configuration, but that
 37           might not be backward compatible with previous kernels.
 38 
 39           If backward compatibility is not an issue, then it is safe and
 40           recommended to say N here.
 41 
 42           For more information, see Documentation/filesystems/overlayfs.rst
 43 
 44           If unsure, say Y.
 45 
 46 config OVERLAY_FS_INDEX
 47         bool "Overlayfs: turn on inodes index feature by default"
 48         depends on OVERLAY_FS
 49         help
 50           If this config option is enabled then overlay filesystems will use
 51           the index directory to map lower inodes to upper inodes by default.
 52           In this case it is still possible to turn off index globally with the
 53           "index=off" module option or on a filesystem instance basis with the
 54           "index=off" mount option.
 55 
 56           The inodes index feature prevents breaking of lower hardlinks on copy
 57           up.
 58 
 59           Note, that the inodes index feature is not backward compatible.
 60           That is, mounting an overlay which has an inodes index on a kernel
 61           that doesn't support this feature will have unexpected results.
 62 
 63           If unsure, say N.
 64 
 65 config OVERLAY_FS_NFS_EXPORT
 66         bool "Overlayfs: turn on NFS export feature by default"
 67         depends on OVERLAY_FS
 68         depends on OVERLAY_FS_INDEX
 69         depends on !OVERLAY_FS_METACOPY
 70         help
 71           If this config option is enabled then overlay filesystems will use
 72           the index directory to decode overlay NFS file handles by default.
 73           In this case, it is still possible to turn off NFS export support
 74           globally with the "nfs_export=off" module option or on a filesystem
 75           instance basis with the "nfs_export=off" mount option.
 76 
 77           The NFS export feature creates an index on copy up of every file and
 78           directory.  This full index is used to detect overlay filesystems
 79           inconsistencies on lookup, like redirect from multiple upper dirs to
 80           the same lower dir.  The full index may incur some overhead on mount
 81           time, especially when verifying that directory file handles are not
 82           stale.
 83 
 84           Note, that the NFS export feature is not backward compatible.
 85           That is, mounting an overlay which has a full index on a kernel
 86           that doesn't support this feature will have unexpected results.
 87 
 88           Most users should say N here and enable this feature on a case-by-
 89           case basis with the "nfs_export=on" mount option.
 90 
 91           Say N unless you fully understand the consequences.
 92 
 93 config OVERLAY_FS_XINO_AUTO
 94         bool "Overlayfs: auto enable inode number mapping"
 95         default n
 96         depends on OVERLAY_FS
 97         depends on 64BIT
 98         help
 99           If this config option is enabled then overlay filesystems will use
100           unused high bits in underlying filesystem inode numbers to map all
101           inodes to a unified address space.  The mapped 64bit inode numbers
102           might not be compatible with applications that expect 32bit inodes.
103 
104           If compatibility with applications that expect 32bit inodes is not an
105           issue, then it is safe and recommended to say Y here.
106 
107           For more information, see Documentation/filesystems/overlayfs.rst
108 
109           If unsure, say N.
110 
111 config OVERLAY_FS_METACOPY
112         bool "Overlayfs: turn on metadata only copy up feature by default"
113         depends on OVERLAY_FS
114         select OVERLAY_FS_REDIRECT_DIR
115         help
116           If this config option is enabled then overlay filesystems will
117           copy up only metadata where appropriate and data copy up will
118           happen when a file is opened for WRITE operation. It is still
119           possible to turn off this feature globally with the "metacopy=off"
120           module option or on a filesystem instance basis with the
121           "metacopy=off" mount option.
122 
123           Note, that this feature is not backward compatible.  That is,
124           mounting an overlay which has metacopy only inodes on a kernel
125           that doesn't support this feature will have unexpected results.
126 
127           If unsure, say N.
128 
129 config OVERLAY_FS_DEBUG
130         bool "Overlayfs: turn on extra debugging checks"
131         default n
132         depends on OVERLAY_FS
133         help
134           Say Y here to enable extra debugging checks in overlayfs.
135 
136           If unsure, say N.

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