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