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Diffstat (limited to 'Documentation/filesystems/overlayfs.rst')
| -rw-r--r-- | Documentation/filesystems/overlayfs.rst | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index cdefbe73d85c..0407f361f32a 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -339,6 +339,19 @@ The specified lower directories will be stacked beginning from the rightmost one and going left. In the above example lower1 will be the top, lower2 the middle and lower3 the bottom layer. +Note: directory names containing colons can be provided as lower layer by +escaping the colons with a single backslash. For example: + + mount -t overlay overlay -olowerdir=/a\:lower\:\:dir /merged + +Since kernel version v6.8, directory names containing colons can also +be configured as lower layer using the "lowerdir+" mount options and the +fsconfig syscall from new mount api. For example: + + fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/a:lower::dir", 0); + +In the latter case, colons in lower layer directory names will be escaped +as an octal characters (\072) when displayed in /proc/self/mountinfo. Metadata only copy up --------------------- @@ -404,6 +417,16 @@ Only the data of the files in the "data-only" lower layers may be visible when a "metacopy" file in one of the lower layers above it, has a "redirect" to the absolute path of the "lower data" file in the "data-only" lower layer. +Since kernel version v6.8, "data-only" lower layers can also be added using +the "datadir+" mount options and the fsconfig syscall from new mount api. +For example: + + fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/l1", 0); + fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/l2", 0); + fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/l3", 0); + fsconfig(fs_fd, FSCONFIG_SET_STRING, "datadir+", "/do1", 0); + fsconfig(fs_fd, FSCONFIG_SET_STRING, "datadir+", "/do2", 0); + fs-verity support ---------------------- @@ -492,6 +515,29 @@ directory tree on the same or different underlying filesystem, and even to a different machine. With the "inodes index" feature, trying to mount the copied layers will fail the verification of the lower root file handle. +Nesting overlayfs mounts +------------------------ + +It is possible to use a lower directory that is stored on an overlayfs +mount. For regular files this does not need any special care. However, files +that have overlayfs attributes, such as whiteouts or "overlay.*" xattrs will be +interpreted by the underlying overlayfs mount and stripped out. In order to +allow the second overlayfs mount to see the attributes they must be escaped. + +Overlayfs specific xattrs are escaped by using a special prefix of +"overlay.overlay.". So, a file with a "trusted.overlay.overlay.metacopy" xattr +in the lower dir will be exposed as a regular file with a +"trusted.overlay.metacopy" xattr in the overlayfs mount. This can be nested by +repeating the prefix multiple time, as each instance only removes one prefix. + +A lower dir with a regular whiteout will always be handled by the overlayfs +mount, so to support storing an effective whiteout file in an overlayfs mount an +alternative form of whiteout is supported. This form is a regular, zero-size +file with the "overlay.whiteout" xattr set, inside a directory with the +"overlay.whiteouts" xattr set. Such whiteouts are never created by overlayfs, +but can be used by userspace tools (like containers) that generate lower layers. +These alternative whiteouts can be escaped using the standard xattr escape +mechanism in order to properly nest to any depth. Non-standard behavior --------------------- |