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autofs: update autofs.txt for strictexpire mount option 

A "strictexpire" mount option has been added to the autofs file system.

It is meant to be used in cases where a GUI continually accesses or an
application frquently scans an automount directory tree causing an
accumulation of otherwise unused mounts.

Link: http://lkml.kernel.org/r/155287083000.12593.2722713092537666885.stgit@pluto.themaw.net
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ian Kent 2019-05-14 15:44:17 -07:00 committed by Linus Torvalds
parent 2ad56addb9
commit 9200026623
1 changed files with 12 additions and 5 deletions
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17
Documentation/filesystems/autofs.txt
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@ -240,11 +240,18 @@ Normally the daemon only wants to remove entries which haven't been
used for a while. For this purpose autofs maintains a "`last_used`"
time stamp on each directory or symlink. For symlinks it genuinely
does record the last time the symlink was "used" or followed to find
out where it points to. For directories the field is a slight
misnomer. It actually records the last time that autofs checked if
the directory or one of its descendants was busy and found that it
was. This is just as useful and doesn't require updating the field so
often.
out where it points to. For directories the field is used slightly
differently. The field is updated at mount time and during expire
checks if it is found to be in use (ie. open file descriptor or
process working directory) and during path walks. The update done
during path walks prevents frequent expire and immediate mount of
frequently accessed automounts. But in the case where a GUI continually
access or an application frequently scans an autofs directory tree
there can be an accumulation of mounts that aren't actually being
used. To cater for this case the "`strictexpire`" autofs mount option
can be used to avoid the "`last_used`" update on path walk thereby
preventing this apparent inability to expire mounts that aren't
really in use.
The daemon is able to ask autofs if anything is due to be expired,
using an `ioctl` as discussed later. For a *direct* mount, autofs