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99ff6cf0 N |
1 | Support is available for filesystems that wish to do automounting |
2 | support (such as kAFS which can be found in fs/afs/ and NFS in | |
3 | fs/nfs/). This facility includes allowing in-kernel mounts to be | |
4 | performed and mountpoint degradation to be requested. The latter can | |
5 | also be requested by userspace. | |
1da177e4 LT |
6 | |
7 | ||
8 | ====================== | |
9 | IN-KERNEL AUTOMOUNTING | |
10 | ====================== | |
11 | ||
99ff6cf0 | 12 | See section "Mount Traps" of Documentation/filesystems/autofs4.txt |
1da177e4 LT |
13 | |
14 | Then from userspace, you can just do something like: | |
15 | ||
16 | [root@andromeda root]# mount -t afs \#root.afs. /afs | |
17 | [root@andromeda root]# ls /afs | |
18 | asd cambridge cambridge.redhat.com grand.central.org | |
19 | [root@andromeda root]# ls /afs/cambridge | |
20 | afsdoc | |
21 | [root@andromeda root]# ls /afs/cambridge/afsdoc/ | |
22 | ChangeLog html LICENSE pdf RELNOTES-1.2.2 | |
23 | ||
24 | And then if you look in the mountpoint catalogue, you'll see something like: | |
25 | ||
26 | [root@andromeda root]# cat /proc/mounts | |
27 | ... | |
28 | #root.afs. /afs afs rw 0 0 | |
29 | #root.cell. /afs/cambridge.redhat.com afs rw 0 0 | |
30 | #afsdoc. /afs/cambridge.redhat.com/afsdoc afs rw 0 0 | |
31 | ||
32 | ||
33 | =========================== | |
34 | AUTOMATIC MOUNTPOINT EXPIRY | |
35 | =========================== | |
36 | ||
37 | Automatic expiration of mountpoints is easy, provided you've mounted the | |
99ff6cf0 | 38 | mountpoint to be expired in the automounting procedure outlined separately. |
1da177e4 LT |
39 | |
40 | To do expiration, you need to follow these steps: | |
41 | ||
99ff6cf0 N |
42 | (1) Create at least one list off which the vfsmounts to be expired can be |
43 | hung. | |
1da177e4 | 44 | |
99ff6cf0 N |
45 | (2) When a new mountpoint is created in the ->d_automount method, add |
46 | the mnt to the list using mnt_set_expiry() | |
47 | mnt_set_expiry(newmnt, &afs_vfsmounts); | |
1da177e4 | 48 | |
99ff6cf0 | 49 | (3) When you want mountpoints to be expired, call mark_mounts_for_expiry() |
1da177e4 LT |
50 | with a pointer to this list. This will process the list, marking every |
51 | vfsmount thereon for potential expiry on the next call. | |
52 | ||
53 | If a vfsmount was already flagged for expiry, and if its usage count is 1 | |
54 | (it's only referenced by its parent vfsmount), then it will be deleted | |
55 | from the namespace and thrown away (effectively unmounted). | |
56 | ||
57 | It may prove simplest to simply call this at regular intervals, using | |
58 | some sort of timed event to drive it. | |
59 | ||
60 | The expiration flag is cleared by calls to mntput. This means that expiration | |
61 | will only happen on the second expiration request after the last time the | |
62 | mountpoint was accessed. | |
63 | ||
64 | If a mountpoint is moved, it gets removed from the expiration list. If a bind | |
65 | mount is made on an expirable mount, the new vfsmount will not be on the | |
66 | expiration list and will not expire. | |
67 | ||
68 | If a namespace is copied, all mountpoints contained therein will be copied, | |
69 | and the copies of those that are on an expiration list will be added to the | |
70 | same expiration list. | |
71 | ||
72 | ||
73 | ======================= | |
74 | USERSPACE DRIVEN EXPIRY | |
75 | ======================= | |
76 | ||
77 | As an alternative, it is possible for userspace to request expiry of any | |
78 | mountpoint (though some will be rejected - the current process's idea of the | |
79 | rootfs for example). It does this by passing the MNT_EXPIRE flag to | |
80 | umount(). This flag is considered incompatible with MNT_FORCE and MNT_DETACH. | |
81 | ||
82 | If the mountpoint in question is in referenced by something other than | |
83 | umount() or its parent mountpoint, an EBUSY error will be returned and the | |
84 | mountpoint will not be marked for expiration or unmounted. | |
85 | ||
86 | If the mountpoint was not already marked for expiry at that time, an EAGAIN | |
87 | error will be given and it won't be unmounted. | |
88 | ||
89 | Otherwise if it was already marked and it wasn't referenced, unmounting will | |
90 | take place as usual. | |
91 | ||
92 | Again, the expiration flag is cleared every time anything other than umount() | |
93 | looks at a mountpoint. |