1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 ================= 3 =================
4 Automount Support 4 Automount Support
5 ================= 5 =================
6 6
7 7
8 Support is available for filesystems that wish 8 Support is available for filesystems that wish to do automounting
9 support (such as kAFS which can be found in fs 9 support (such as kAFS which can be found in fs/afs/ and NFS in
10 fs/nfs/). This facility includes allowing in-k 10 fs/nfs/). This facility includes allowing in-kernel mounts to be
11 performed and mountpoint degradation to be req 11 performed and mountpoint degradation to be requested. The latter can
12 also be requested by userspace. 12 also be requested by userspace.
13 13
14 14
15 In-Kernel Automounting 15 In-Kernel Automounting
16 ====================== 16 ======================
17 17
18 See section "Mount Traps" of Documentation/fi 18 See section "Mount Traps" of Documentation/filesystems/autofs.rst
19 19
20 Then from userspace, you can just do something 20 Then from userspace, you can just do something like::
21 21
22 [root@andromeda root]# mount -t afs \# 22 [root@andromeda root]# mount -t afs \#root.afs. /afs
23 [root@andromeda root]# ls /afs 23 [root@andromeda root]# ls /afs
24 asd cambridge cambridge.redhat.com 24 asd cambridge cambridge.redhat.com grand.central.org
25 [root@andromeda root]# ls /afs/cambrid 25 [root@andromeda root]# ls /afs/cambridge
26 afsdoc 26 afsdoc
27 [root@andromeda root]# ls /afs/cambrid 27 [root@andromeda root]# ls /afs/cambridge/afsdoc/
28 ChangeLog html LICENSE pdf RELNOTE 28 ChangeLog html LICENSE pdf RELNOTES-1.2.2
29 29
30 And then if you look in the mountpoint catalog 30 And then if you look in the mountpoint catalogue, you'll see something like::
31 31
32 [root@andromeda root]# cat /proc/mount 32 [root@andromeda root]# cat /proc/mounts
33 ... 33 ...
34 #root.afs. /afs afs rw 0 0 34 #root.afs. /afs afs rw 0 0
35 #root.cell. /afs/cambridge.redhat.com 35 #root.cell. /afs/cambridge.redhat.com afs rw 0 0
36 #afsdoc. /afs/cambridge.redhat.com/afs 36 #afsdoc. /afs/cambridge.redhat.com/afsdoc afs rw 0 0
37 37
38 38
39 Automatic Mountpoint Expiry 39 Automatic Mountpoint Expiry
40 =========================== 40 ===========================
41 41
42 Automatic expiration of mountpoints is easy, p 42 Automatic expiration of mountpoints is easy, provided you've mounted the
43 mountpoint to be expired in the automounting p 43 mountpoint to be expired in the automounting procedure outlined separately.
44 44
45 To do expiration, you need to follow these ste 45 To do expiration, you need to follow these steps:
46 46
47 (1) Create at least one list off which the vf 47 (1) Create at least one list off which the vfsmounts to be expired can be
48 hung. 48 hung.
49 49
50 (2) When a new mountpoint is created in the - 50 (2) When a new mountpoint is created in the ->d_automount method, add
51 the mnt to the list using mnt_set_expiry( 51 the mnt to the list using mnt_set_expiry()::
52 52
53 mnt_set_expiry(newmnt, &afs_vfsmo 53 mnt_set_expiry(newmnt, &afs_vfsmounts);
54 54
55 (3) When you want mountpoints to be expired, 55 (3) When you want mountpoints to be expired, call mark_mounts_for_expiry()
56 with a pointer to this list. This will pr 56 with a pointer to this list. This will process the list, marking every
57 vfsmount thereon for potential expiry on 57 vfsmount thereon for potential expiry on the next call.
58 58
59 If a vfsmount was already flagged for exp 59 If a vfsmount was already flagged for expiry, and if its usage count is 1
60 (it's only referenced by its parent vfsmo 60 (it's only referenced by its parent vfsmount), then it will be deleted
61 from the namespace and thrown away (effec 61 from the namespace and thrown away (effectively unmounted).
62 62
63 It may prove simplest to simply call this 63 It may prove simplest to simply call this at regular intervals, using
64 some sort of timed event to drive it. 64 some sort of timed event to drive it.
65 65
66 The expiration flag is cleared by calls to mnt 66 The expiration flag is cleared by calls to mntput. This means that expiration
67 will only happen on the second expiration requ 67 will only happen on the second expiration request after the last time the
68 mountpoint was accessed. 68 mountpoint was accessed.
69 69
70 If a mountpoint is moved, it gets removed from 70 If a mountpoint is moved, it gets removed from the expiration list. If a bind
71 mount is made on an expirable mount, the new v 71 mount is made on an expirable mount, the new vfsmount will not be on the
72 expiration list and will not expire. 72 expiration list and will not expire.
73 73
74 If a namespace is copied, all mountpoints cont 74 If a namespace is copied, all mountpoints contained therein will be copied,
75 and the copies of those that are on an expirat 75 and the copies of those that are on an expiration list will be added to the
76 same expiration list. 76 same expiration list.
77 77
78 78
79 Userspace Driven Expiry 79 Userspace Driven Expiry
80 ======================= 80 =======================
81 81
82 As an alternative, it is possible for userspac 82 As an alternative, it is possible for userspace to request expiry of any
83 mountpoint (though some will be rejected - the 83 mountpoint (though some will be rejected - the current process's idea of the
84 rootfs for example). It does this by passing t 84 rootfs for example). It does this by passing the MNT_EXPIRE flag to
85 umount(). This flag is considered incompatible 85 umount(). This flag is considered incompatible with MNT_FORCE and MNT_DETACH.
86 86
87 If the mountpoint in question is in referenced 87 If the mountpoint in question is in referenced by something other than
88 umount() or its parent mountpoint, an EBUSY er 88 umount() or its parent mountpoint, an EBUSY error will be returned and the
89 mountpoint will not be marked for expiration o 89 mountpoint will not be marked for expiration or unmounted.
90 90
91 If the mountpoint was not already marked for e 91 If the mountpoint was not already marked for expiry at that time, an EAGAIN
92 error will be given and it won't be unmounted. 92 error will be given and it won't be unmounted.
93 93
94 Otherwise if it was already marked and it wasn 94 Otherwise if it was already marked and it wasn't referenced, unmounting will
95 take place as usual. 95 take place as usual.
96 96
97 Again, the expiration flag is cleared every ti 97 Again, the expiration flag is cleared every time anything other than umount()
98 looks at a mountpoint. 98 looks at a mountpoint.
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