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