Lines Matching +full:group +full:- +full:index +full:- +full:bits
1 .. SPDX-License-Identifier: GPL-2.0
10 overlay-filesystem functionality in Linux (sometimes referred to as
11 union-filesystems). An overlay-filesystem tries to present a
17 ---------------
25 While directories will report an st_dev from the overlay-filesystem,
26 non-directory objects may report an st_dev from the lower filesystem or
29 over the lifetime of a non-directory object. Many applications and
43 The "xino" feature uses the high inode number bits for fsid, because the
44 underlying filesystems rarely use the high inode number bits. In case
45 the underlying inode number does overflow into the high xino bits, overlay
48 The "xino" feature can be enabled with the "-o xino=on" overlay mount option.
51 the lifetime of the filesystem. The "-o xino=auto" overlay mount option
60 +--------------+------------+------------+-----------------+----------------+
65 +--------------+-----+------+-----+------+--------+--------+--------+-------+
68 +--------------+-----+------+-----+------+--------+--------+--------+-------+
72 +--------------+-----+------+-----+------+--------+--------+--------+-------+
74 +--------------+-----+------+-----+------+--------+--------+--------+-------+
77 +--------------+-----+------+-----+------+--------+--------+--------+-------+
84 ---------------
86 An overlay filesystem combines two filesystems - an 'upper' filesystem
106 A read-only overlay of two read-only filesystems may use any
110 -----------
113 upper and lower filesystems and refers to a non-directory in either,
114 then the lower object is hidden - the name refers only to the upper
123 mount -t overlay overlay -olowerdir=/lower,upperdir=/upper,\
141 --------------------------------
146 directories (non-directories are always opaque).
149 as a zero-size regular file with the xattr "trusted.overlay.whiteout".
167 -------
171 obvious way (upper is read first, then lower - entries that already
172 exist are not re-added). This merged name list is cached in the
186 - read part of a directory
187 - remember an offset, and close the directory
188 - re-open the directory some time later
189 - seek to the remembered offset
199 --------------------
220 - OVERLAY_FS_REDIRECT_DIR:
222 - OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW:
230 - "redirect_dir=BOOL":
232 - "redirect_always_follow=BOOL":
234 - "redirect_max=NUM":
239 - "redirect_dir=on":
241 - "redirect_dir=follow":
243 - "redirect_dir=nofollow":
245 - "redirect_dir=off":
252 on the index entry. On lookup of a merged directory, if the upper
253 directory does not match the file handle stores in the index, that is an
258 Because lower layer redirects cannot be verified with the index, enabling
263 Non-directories
264 ---------------
266 Objects that are not directories (files, symlinks, device-special
269 the requires write-access, such as opening for write access, changing
271 to the upper filesystem (copy_up). Note that creating a hard-link
276 opened for read-write but the data is not modified.
279 exists in the upper filesystem - creating it and any parents as
281 mode, mtime, symlink-target etc.) and then if the object is a file, the
287 filesystem - future operations on the file are barely noticed by the
293 ----------------
301 3) non-mounting task MAY gain additional privileges through the overlay,
307 group, mode and posix acl), as well as MAC checks
313 Check (a) ensures consistency (1) since owner, group, mode and posix acls
325 mount -t overlay overlay -olowerdir=/lower,upperdir=/upper,... /merged
329 cp -a /lower /upper
330 mount --bind /upper /merged
333 the time of copy (on-demand vs. up-front).
337 ---------------------
342 mount -t overlay overlay -olowerdir=/lower1:/lower2:/lower3 /merged
345 that case the overlay will be read-only.
354 mount -t overlay overlay -olowerdir=/a\:lower\:\:dir /merged
366 ---------------------
399 Data-only lower layers
400 ----------------------
415 as "data-only" lower layers, using double colon ("::") separators.
416 A normal lower layer is not allowed to be below a data-only layer, so single
422 mount -t overlay overlay -olowerdir=/l1:/l2:/l3::/do1::/do2 /merged
424 The paths of files in the "data-only" lower layers are not visible in the
426 in the "data-only" lower layers are not visible in overlayfs inodes.
428 Only the data of the files in the "data-only" lower layers may be visible
430 to the absolute path of the "lower data" file in the "data-only" lower layer.
432 Since kernel version v6.8, "data-only" lower layers can also be added using
443 fs-verity support
444 -----------------
447 fs-verity enabled and overlay verity support is enabled, then the
454 that was in the lower at the time of the copy-up. If at any time
458 digest check, or from a later read due to fs-verity) and a detailed
459 error is printed to the kernel logs. For more details of how fs-verity
466 layer is fully trusted (by using dm-verity or something similar), then
469 directories are specified as "Data-only", then they can only supply
476 - "off":
479 - "on":
484 - "require":
487 will only be used if the data file has fs-verity enabled,
488 otherwise a full copy-up is used.
491 --------------------------
507 different lower layer path, is allowed, unless the "index" or "metacopy"
510 With the "index" feature, on the first time mount, an NFS file
517 "index" enabled will fail with EOPNOTSUPP if the lower filesystem
527 to a different machine. With the "index" feature, trying to mount
531 ------------------------
547 alternative form of whiteout is supported. This form is a regular, zero-size
555 Non-standard behavior
556 ---------------------
566 b) If a file residing on a lower layer is opened for read-only and then
583 will fail with EXDEV ("Invalid cross-device link").
585 index section in Non-standard behavior
588 Enabled with the mount option or module option "index=on" or with the
604 enough free bits in the inode number, then overlayfs will not be able to
614 ---------------------------------
623 "metacopy", "index", "xino" and "redirect_dir" features
647 ----------
652 With the "nfs_export" feature, on copy_up of any lower object, an index
653 entry is created under the index directory. The index entry name is the
655 non-directory object, the index entry is a hard link to the upper inode.
656 For a directory object, the index entry has an extended attribute
663 1. For a non-upper object, encode a lower file handle from lower inode
665 3. For a pure-upper object and for an existing non-indexed upper object,
670 - Header including path type information (e.g. lower/upper)
671 - UUID of the underlying filesystem
672 - Underlying filesystem encoding of underlying inode
681 3. For a lower file handle, lookup the handle in index directory by name.
682 4. If a whiteout is found in index, return ESTALE. This represents an
684 5. For a non-directory, instantiate a disconnected overlay dentry from the
685 decoded underlying dentry, the path type and index inode, if found.
687 and index, to lookup a connected overlay dentry.
689 Decoding a non-directory file handle may return a disconnected dentry.
690 copy_up of that disconnected dentry will create an upper index entry with
706 The overlay filesystem does not support non-directory connectable file
710 When the NFS export feature is enabled, all directory index entries are
714 Note: the mount options index=off,nfs_export=on are conflicting for a
715 read-write mount and will result in an error.
725 -------------
730 - "null":
732 - "off":
735 - "on":
740 - "auto": (default)
749 --------------
777 ----------
779 The "-o userxattr" mount option forces overlayfs to use the
785 ---------
790 https://github.com/amir73il/unionmount-testsuite.git
794 # cd unionmount-testsuite
795 # ./run --ov --verify