Autofs, Cambridge 2014

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Autofs Edward Tomasz Napierała / FreeBSD Foundation What's an automounter? • Have all filesystems accessible all the time, without keeping them mounted. • Dynamic maps, to avoid configuring every single mount • Centralized maps (LDAP) What's wrong with amd(8)? • Map format different from Sun • No LDAP in base, so amd(8) gets built without it • Calls mount(2) syscall directly • Userland NFS magic, the evil kind Autofs project scope • Cleanroom reimplementation • Proper autofs(4) • "Industry standard" map format • Directory services (LDAP) • Can mount any filesystem • Scripts, man pages, handbook Maps • auto_master(5) references individual maps # $FreeBSD$ # # Automounter master map, see auto_master(5) for details. # /net -hosts -nosuid /auto/groups autofs.group +auto.master • Maps define actual remote filesystems SLES10 -rw,nosuid elmer:/vol/vol3/sys-li9/& • Direct vs indirect maps autofs(4) • Very simple filesystem, less than 1KLOC • Triggering mechanism • Simple directory hierarchy for indirect maps • VOP forwarding to the newly mounted vnode automount(8) • Sets up autofs(4) mounts based on auto_master(5) and indirect maps • Runs during startup, or manually after auto_master(5) modification • Some utility functions, eg. "automount -u". automountd(8) • Daemon handling trigger requests from autofs(4) • Locates the map, parses it, runs mount command • One process per request; no need to be asynchronous • No state; can be restarted at any time autounmountd(8) • Watches for filesystem events using kqueue(2), records mount time, unmounts after a while • Only touches filesystems with "automounted" mount option set Extensibility • How special maps are just shell scripts • Easy to modify to fit existing LDAP infrastructure, eg removing unsupported mount options • Working around not having OpenLDAP in base • Trivial debugging - just run the script by hand Reliability • Retries, for transient network problems • Timeouts, to not wedge the system indefinitely • Cache, to avoid unnceccessary requests • ^C at any time Demo! Problems • Never block automountd(8) or any of its children, mount(8) in particular • Interaction with fts(3) • Lack of hierarchical mounts • Duplicated mounts Questions? (https://github.com/trasz/autofs).

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