1# SPDX-License-Identifier: GPL-2.0-only 2config 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 15config 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 31config 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 46config 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 65config 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 93config 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 111config 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 129config 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. 137