1ef94b186SMiklos Szerediconfig OVERLAY_FS 2e9be9d5eSMiklos Szeredi tristate "Overlay filesystem support" 372d42504SArnd Bergmann select EXPORTFS 4e9be9d5eSMiklos Szeredi help 5e9be9d5eSMiklos Szeredi An overlay filesystem combines two filesystems - an 'upper' filesystem 6e9be9d5eSMiklos Szeredi and a 'lower' filesystem. When a name exists in both filesystems, the 7e9be9d5eSMiklos Szeredi object in the 'upper' filesystem is visible while the object in the 8e9be9d5eSMiklos Szeredi 'lower' filesystem is either hidden or, in the case of directories, 9e9be9d5eSMiklos Szeredi merged with the 'upper' object. 10e9be9d5eSMiklos Szeredi 11e9be9d5eSMiklos Szeredi For more information see Documentation/filesystems/overlayfs.txt 12688ea0e5SMiklos Szeredi 13688ea0e5SMiklos Szerediconfig OVERLAY_FS_REDIRECT_DIR 14688ea0e5SMiklos Szeredi bool "Overlayfs: turn on redirect dir feature by default" 15688ea0e5SMiklos Szeredi depends on OVERLAY_FS 16688ea0e5SMiklos Szeredi help 17688ea0e5SMiklos Szeredi If this config option is enabled then overlay filesystems will use 18688ea0e5SMiklos Szeredi redirects when renaming directories by default. In this case it is 19688ea0e5SMiklos Szeredi still possible to turn off redirects globally with the 20688ea0e5SMiklos Szeredi "redirect_dir=off" module option or on a filesystem instance basis 21688ea0e5SMiklos Szeredi with the "redirect_dir=off" mount option. 22688ea0e5SMiklos Szeredi 23688ea0e5SMiklos Szeredi Note, that redirects are not backward compatible. That is, mounting 24688ea0e5SMiklos Szeredi an overlay which has redirects on a kernel that doesn't support this 25688ea0e5SMiklos Szeredi feature will have unexpected results. 2602bcd157SAmir Goldstein 2702bcd157SAmir Goldsteinconfig OVERLAY_FS_INDEX 2802bcd157SAmir Goldstein bool "Overlayfs: turn on inodes index feature by default" 2902bcd157SAmir Goldstein depends on OVERLAY_FS 3002bcd157SAmir Goldstein help 3102bcd157SAmir Goldstein If this config option is enabled then overlay filesystems will use 3202bcd157SAmir Goldstein the inodes index dir to map lower inodes to upper inodes by default. 3302bcd157SAmir Goldstein In this case it is still possible to turn off index globally with the 3402bcd157SAmir Goldstein "index=off" module option or on a filesystem instance basis with the 3502bcd157SAmir Goldstein "index=off" mount option. 3602bcd157SAmir Goldstein 3702bcd157SAmir Goldstein The inodes index feature prevents breaking of lower hardlinks on copy 3802bcd157SAmir Goldstein up. 3902bcd157SAmir Goldstein 4002bcd157SAmir Goldstein Note, that the inodes index feature is read-only backward compatible. 4102bcd157SAmir Goldstein That is, mounting an overlay which has an index dir on a kernel that 4202bcd157SAmir Goldstein doesn't support this feature read-only, will not have any negative 4302bcd157SAmir Goldstein outcomes. However, mounting the same overlay with an old kernel 4402bcd157SAmir Goldstein read-write and then mounting it again with a new kernel, will have 4502bcd157SAmir Goldstein unexpected results. 46