fs/overlayfs/Kconfig

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