tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1# SPDX-License-Identifier: GPL-2.0-only
2config OVERLAY_FS
3 tristate "Overlay filesystem support"
4 select FS_STACK
5 select EXPORTFS
6 help
7 An overlay filesystem combines two filesystems - an 'upper' filesystem
8 and a 'lower' filesystem. When a name exists in both filesystems, the
9 object in the 'upper' filesystem is visible while the object in the
10 'lower' filesystem is either hidden or, in the case of directories,
11 merged with the 'upper' object.
12
13 For more information see Documentation/filesystems/overlayfs.rst
14
15config OVERLAY_FS_REDIRECT_DIR
16 bool "Overlayfs: turn on redirect directory feature by default"
17 depends on OVERLAY_FS
18 help
19 If this config option is enabled then overlay filesystems will use
20 redirects when renaming directories by default. In this case it is
21 still possible to turn off redirects globally with the
22 "redirect_dir=off" module option or on a filesystem instance basis
23 with the "redirect_dir=off" mount option.
24
25 Note, that redirects are not backward compatible. That is, mounting
26 an overlay which has redirects on a kernel that doesn't support this
27 feature will have unexpected results.
28
29 If unsure, say N.
30
31config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW
32 bool "Overlayfs: follow redirects even if redirects are turned off"
33 default y
34 depends on OVERLAY_FS
35 help
36 Disable this to get a possibly more secure configuration, but that
37 might not be backward compatible with previous kernels.
38
39 If backward compatibility is not an issue, then it is safe and
40 recommended to say N here.
41
42 For more information, see Documentation/filesystems/overlayfs.rst
43
44 If unsure, say Y.
45
46config OVERLAY_FS_INDEX
47 bool "Overlayfs: turn on inodes index feature by default"
48 depends on OVERLAY_FS
49 help
50 If this config option is enabled then overlay filesystems will use
51 the index directory to map lower inodes to upper inodes by default.
52 In this case it is still possible to turn off index globally with the
53 "index=off" module option or on a filesystem instance basis with the
54 "index=off" mount option.
55
56 The inodes index feature prevents breaking of lower hardlinks on copy
57 up.
58
59 Note, that the inodes index feature is not backward compatible.
60 That is, mounting an overlay which has an inodes index on a kernel
61 that doesn't support this feature will have unexpected results.
62
63 If unsure, say N.
64
65config OVERLAY_FS_NFS_EXPORT
66 bool "Overlayfs: turn on NFS export feature by default"
67 depends on OVERLAY_FS
68 depends on OVERLAY_FS_INDEX
69 depends on !OVERLAY_FS_METACOPY
70 help
71 If this config option is enabled then overlay filesystems will use
72 the index directory to decode overlay NFS file handles by default.
73 In this case, it is still possible to turn off NFS export support
74 globally with the "nfs_export=off" module option or on a filesystem
75 instance basis with the "nfs_export=off" mount option.
76
77 The NFS export feature creates an index on copy up of every file and
78 directory. This full index is used to detect overlay filesystems
79 inconsistencies on lookup, like redirect from multiple upper dirs to
80 the same lower dir. The full index may incur some overhead on mount
81 time, especially when verifying that directory file handles are not
82 stale.
83
84 Note, that the NFS export feature is not backward compatible.
85 That is, mounting an overlay which has a full index on a kernel
86 that doesn't support this feature will have unexpected results.
87
88 Most users should say N here and enable this feature on a case-by-
89 case basis with the "nfs_export=on" mount option.
90
91 Say N unless you fully understand the consequences.
92
93config OVERLAY_FS_XINO_AUTO
94 bool "Overlayfs: auto enable inode number mapping"
95 default n
96 depends on OVERLAY_FS
97 depends on 64BIT
98 help
99 If this config option is enabled then overlay filesystems will use
100 unused high bits in underlying filesystem inode numbers to map all
101 inodes to a unified address space. The mapped 64bit inode numbers
102 might not be compatible with applications that expect 32bit inodes.
103
104 If compatibility with applications that expect 32bit inodes is not an
105 issue, then it is safe and recommended to say Y here.
106
107 For more information, see Documentation/filesystems/overlayfs.rst
108
109 If unsure, say N.
110
111config OVERLAY_FS_METACOPY
112 bool "Overlayfs: turn on metadata only copy up feature by default"
113 depends on OVERLAY_FS
114 select OVERLAY_FS_REDIRECT_DIR
115 help
116 If this config option is enabled then overlay filesystems will
117 copy up only metadata where appropriate and data copy up will
118 happen when a file is opened for WRITE operation. It is still
119 possible to turn off this feature globally with the "metacopy=off"
120 module option or on a filesystem instance basis with the
121 "metacopy=off" mount option.
122
123 Note, that this feature is not backward compatible. That is,
124 mounting an overlay which has metacopy only inodes on a kernel
125 that doesn't support this feature will have unexpected results.
126
127 If unsure, say N.
128
129config OVERLAY_FS_DEBUG
130 bool "Overlayfs: turn on extra debugging checks"
131 default n
132 depends on OVERLAY_FS
133 help
134 Say Y here to enable extra debugging checks in overlayfs.
135
136 If unsure, say N.