99 строки
3.5 KiB
ReStructuredText
99 строки
3.5 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
=================
|
|
Automount Support
|
|
=================
|
|
|
|
|
|
Support is available for filesystems that wish to do automounting
|
|
support (such as kAFS which can be found in fs/afs/ and NFS in
|
|
fs/nfs/). This facility includes allowing in-kernel mounts to be
|
|
performed and mountpoint degradation to be requested. The latter can
|
|
also be requested by userspace.
|
|
|
|
|
|
In-Kernel Automounting
|
|
======================
|
|
|
|
See section "Mount Traps" of Documentation/filesystems/autofs.rst
|
|
|
|
Then from userspace, you can just do something like::
|
|
|
|
[root@andromeda root]# mount -t afs \#root.afs. /afs
|
|
[root@andromeda root]# ls /afs
|
|
asd cambridge cambridge.redhat.com grand.central.org
|
|
[root@andromeda root]# ls /afs/cambridge
|
|
afsdoc
|
|
[root@andromeda root]# ls /afs/cambridge/afsdoc/
|
|
ChangeLog html LICENSE pdf RELNOTES-1.2.2
|
|
|
|
And then if you look in the mountpoint catalogue, you'll see something like::
|
|
|
|
[root@andromeda root]# cat /proc/mounts
|
|
...
|
|
#root.afs. /afs afs rw 0 0
|
|
#root.cell. /afs/cambridge.redhat.com afs rw 0 0
|
|
#afsdoc. /afs/cambridge.redhat.com/afsdoc afs rw 0 0
|
|
|
|
|
|
Automatic Mountpoint Expiry
|
|
===========================
|
|
|
|
Automatic expiration of mountpoints is easy, provided you've mounted the
|
|
mountpoint to be expired in the automounting procedure outlined separately.
|
|
|
|
To do expiration, you need to follow these steps:
|
|
|
|
(1) Create at least one list off which the vfsmounts to be expired can be
|
|
hung.
|
|
|
|
(2) When a new mountpoint is created in the ->d_automount method, add
|
|
the mnt to the list using mnt_set_expiry()::
|
|
|
|
mnt_set_expiry(newmnt, &afs_vfsmounts);
|
|
|
|
(3) When you want mountpoints to be expired, call mark_mounts_for_expiry()
|
|
with a pointer to this list. This will process the list, marking every
|
|
vfsmount thereon for potential expiry on the next call.
|
|
|
|
If a vfsmount was already flagged for expiry, and if its usage count is 1
|
|
(it's only referenced by its parent vfsmount), then it will be deleted
|
|
from the namespace and thrown away (effectively unmounted).
|
|
|
|
It may prove simplest to simply call this at regular intervals, using
|
|
some sort of timed event to drive it.
|
|
|
|
The expiration flag is cleared by calls to mntput. This means that expiration
|
|
will only happen on the second expiration request after the last time the
|
|
mountpoint was accessed.
|
|
|
|
If a mountpoint is moved, it gets removed from the expiration list. If a bind
|
|
mount is made on an expirable mount, the new vfsmount will not be on the
|
|
expiration list and will not expire.
|
|
|
|
If a namespace is copied, all mountpoints contained therein will be copied,
|
|
and the copies of those that are on an expiration list will be added to the
|
|
same expiration list.
|
|
|
|
|
|
Userspace Driven Expiry
|
|
=======================
|
|
|
|
As an alternative, it is possible for userspace to request expiry of any
|
|
mountpoint (though some will be rejected - the current process's idea of the
|
|
rootfs for example). It does this by passing the MNT_EXPIRE flag to
|
|
umount(). This flag is considered incompatible with MNT_FORCE and MNT_DETACH.
|
|
|
|
If the mountpoint in question is in referenced by something other than
|
|
umount() or its parent mountpoint, an EBUSY error will be returned and the
|
|
mountpoint will not be marked for expiration or unmounted.
|
|
|
|
If the mountpoint was not already marked for expiry at that time, an EAGAIN
|
|
error will be given and it won't be unmounted.
|
|
|
|
Otherwise if it was already marked and it wasn't referenced, unmounting will
|
|
take place as usual.
|
|
|
|
Again, the expiration flag is cleared every time anything other than umount()
|
|
looks at a mountpoint.
|