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 dir 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 27config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW 28 bool "Overlayfs: follow redirects even if redirects are turned off" 29 default y 30 depends on OVERLAY_FS 31 help 32 Disable this to get a possibly more secure configuration, but that 33 might not be backward compatible with previous kernels. 34 35 For more information, see Documentation/filesystems/overlayfs.txt 36 37config OVERLAY_FS_INDEX 38 bool "Overlayfs: turn on inodes index feature by default" 39 depends on OVERLAY_FS 40 help 41 If this config option is enabled then overlay filesystems will use 42 the inodes index dir to map lower inodes to upper inodes by default. 43 In this case it is still possible to turn off index globally with the 44 "index=off" module option or on a filesystem instance basis with the 45 "index=off" mount option. 46 47 The inodes index feature prevents breaking of lower hardlinks on copy 48 up. 49 50 Note, that the inodes index feature is not backward compatible. 51 That is, mounting an overlay which has an inodes index on a kernel 52 that doesn't support this feature will have unexpected results. 53 54config OVERLAY_FS_NFS_EXPORT 55 bool "Overlayfs: turn on NFS export feature by default" 56 depends on OVERLAY_FS 57 depends on OVERLAY_FS_INDEX 58 help 59 If this config option is enabled then overlay filesystems will use 60 the inodes index dir to decode overlay NFS file handles by default. 61 In this case, it is still possible to turn off NFS export support 62 globally with the "nfs_export=off" module option or on a filesystem 63 instance basis with the "nfs_export=off" mount option. 64 65 The NFS export feature creates an index on copy up of every file and 66 directory. This full index is used to detect overlay filesystems 67 inconsistencies on lookup, like redirect from multiple upper dirs to 68 the same lower dir. The full index may incur some overhead on mount 69 time, especially when verifying that directory file handles are not 70 stale. 71 72 Note, that the NFS export feature is not backward compatible. 73 That is, mounting an overlay which has a full index on a kernel 74 that doesn't support this feature will have unexpected results. 75