Documentation/filesystems/autofs-mount-control.rst

17 are things such as setting an autofs mount catatonic, setting the
20 mount itself which prevents us being able to use open(2) to obtain a
25 needs to walk back up the mount tree to construct a path, such as
28 from the mount tree.
33 because autofs direct mounts and the implementation of "on demand mount
34 and expire" of nested mount trees have the file system mounted directly
35 on top of the mount trigger directory dentry.
39 a direct mount in disguise) and indirect.
62 operation. So we see a mount of shark:/autofs/export1 on /test/g1, for
65 The way that direct mounts are handled is by making an autofs mount on
66 each full path, such as /automount/dparse/g1, and using it as a mount
67 trigger. So when we walk on the path we mount shark:/autofs/export1 "on
68 top of this mount point". Since these are always directories we can
69 use the follow_link inode operation to trigger the mount.
72 them multi-mount map entries).
74 For example, an indirect mount map entry could also be::
83 and a similarly a direct mount map entry could also be::
94 to mount and umount all of the offsets as a single unit. Not really a
100 In version 5 we mount only as we go down the tree of offsets and
105 above and so the mount points can be covered by a mount.
108 on the mount point for control operations. The references held by the
109 descriptor are accounted for in checks made to determine if a mount is
111 in the mount super block. So the use of a file handle needs to be
120 for these potentially covered autofs mount points. Rather than just
125 In addition, to be able to reconstruct a mount tree that has busy mounts,
126 the uid and gid of the last user that triggered the mount needs to be
128 autofs maps. They are recorded at mount request time and an operation
133 a mount or expire operation completes a status is returned to the
138 very large maps, is discovering if a mount is present. Usually this
141 in the mount table. An operation to lookup the mount status of a mount
158 the mount table which has proved to be a big overhead for users with
161 issued for a mount (file handle) we should continually call back to
164 mount at a time. A Generic Netlink implementation would exclude this
169 autofs Miscellaneous Device mount control interface
202 The ioctlfd field is a mount point file descriptor of an autofs mount
204 the check for whether a given path is a mount point, where it may
205 optionally be used to check a specific mount corresponding to a given
206 mount point file descriptor, and when requesting the uid and gid of the
207 last successful mount on a directory within the autofs file system.
230 not a valid descriptor or doesn't correspond to an autofs mount point
261 with the ioctlfd field set to a valid autofs mount point descriptor
270 Obtain and release a file descriptor for an autofs managed mount point
274 the autofs mount. The device number can be obtained from the mount options
286 Return mount and expire result status from user space to the kernel.
291 mount or expire request. The status field of struct args_fail is set to
299 Normally this is set at mount time using an option but when reconnecting
300 to a existing mount we need to use this to tell the autofs mount about
303 mount be catatonic (see next call).
316 Make the autofs mount point catatonic. The autofs mount will no longer
317 issue mount requests, the kernel communication pipe descriptor is released
327 Set the expire timeout for mounts within an autofs mount point.
337 mount on the given path dentry.
340 field set to the mount point in question and the size field adjusted
344 When reconstructing an autofs mount tree with active mounts we need to
346 gid (or string variations of them) for mount lookups within the map entry.
348 used by user space for the mount map lookups.
354 Issue an expire request to the kernel for an autofs mount. Typically
359 addition an immediate expire that's independent of the mount timeout,
360 and a forced expire that's independent of whether the mount is busy,
366 This call causes the kernel module to check the mount corresponding
373 Checks if an autofs mount point is in use.
387 possible variations. Both use the path field set to the path of the mount
389 ioctlfd field to identify a specific mount point to check while the other
391 set to an autofs mount type. The call returns 1 if this is a mount point
392 and sets out.devid field to the device number of the mount and out.magic
397 If supplied with a file descriptor we're looking for a specific mount,
400 a mountpoint or contains a mount, such as a multi-mount without a root
401 mount. In this case we return 1 if the descriptor corresponds to a mount
402 point and also returns the super magic of the covering mount if there
406 is looked up and is checked to see if it is the root of a mount. If a
407 type is also given we are looking for a particular autofs mount and if
409 root of a mount 1 is returned along with the super magic of the mount