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