Hi This is the initial patch submission of autofs filesystem support for OpenBSD, which was originally written for FreeBSD and later ported to DragonFlyBSD and NetBSD.
Autofs is a generic filesystem automounter filesystem, not limited to mounting NFS. This OpenBSD port actually started off with the NetBSD code rather than FreeBSD though all versions are quite similar except for the autofs filesystem code in kernel space. While I currently maintain it as an out-of-tree filesystem on GitHub, I'm aiming for this to get merged by OpentBSD. The initial patch is available from below in three formats. The patch applies to the current src as of March 24 (and builds on amd64). diff -aNur https://leaf.dragonflybsd.org/~tkusumi/diff/openbsd/OpenBSD-autofs-v1.patch git format-patch https://leaf.dragonflybsd.org/~tkusumi/diff/openbsd/0001-OpenBSD-autofs-v1.patch GitHub https://github.com/kusumi/src/tree/autofs-20180325 Online documentation and man pages for FreeBSD (which are also part of the patch) would/should work against OpenBSD with a few exceptions. Below links are FreeBSD autofs info you can find on the web. Note that FreeBSD autofs is not a port of Linux autofs which has existed for a long(er) time. Although they are quite similar in terms of features, there is no compatibility in configuration files and such, thus the same for OpenBSD and Linux. https://people.freebsd.org/~trasz/autofs.pdf https://wiki.freebsd.org/Automounter http://freebsdfoundation.blogspot.fi/2015/03/freebsd-from-trenches-using-autofs5-to_13.html --- How to use autofs (currently only enabled on amd64) 1. Build kernel (autofs enabled by default atm in sys/conf/GENERIC) and world. 2. Enable etc/rc.d/automountd and etc/rc.d/autounmountd via rcctl(8). 3. Create a character device /dev/autofs via /dev/MAKEDEV. 4. Write auto mount configuration(s) to /etc/auto_master. FreeBSD documentation should help, though configuration needed to do a simple NFS auto mounting is quite simple (2 lines basically - i.e. 1 line in /etc/auto_master to specify a configuration file for eithre direct or indirect map, and 1 line in that file to specify NFS mount details). 5. Run automount(8) command (no options needed) to mount autofs(5) based on /etc/auto_master contents, and confirm autofs(5) is mounted via mount(8) command. 6. Restart automountd(8) and autounmountd(8). This could be before or after running automount(8) command. 7. Access autofs(5) mount point, and see if auto mounting works. I've only tested with NFS with both direct/indirect mapping, which is probably what majority of people use autofs for, however the basic automounting mechanism is filesystem-agnostic. I'll write down some more details of newly added code. --- Newly added subsystems 1. sys/miscfs/autofs The autofs(5) filesystem catches some of the vnode operations, and notifies the user space daemon automountd(8) that auto mounting requests from user process have arrived. The character device /dev/autofs (with major# 98) is used as a communication channel between autofs(5) and automountd(8) daemon via ioctl(2). Once automountd(8) receives the request from autofs(5) filesystem, it attempts to mount a target filesystem which corresponds to the autofs(5) mount point accessed by the user process, based on what auto_master(5) (/etc/auto_master file) has. The actual mounting is done by a child process forked from automountd(8) using mount(8) and variants. 2. usr.sbin/autofs User space is basically the same as the FreeBSD code as well as DragonFlyBSD and NetBSD ports with minimum changes needed for OpenBSD. The changes mostly come from difference in library/syscall interface, FreeBSD specific syscalls, workaround code specific to OpenBSD, etc. The directory contains followings. * autmount(8) - a command to mount autofs(5) filesystem. * automountd(8) - a daemon to auto mount target filesystems specified in /etc/auto_master. * autounmountd(8) - a daemon to auto unmount the auto mounted filesystems if no longer used when the timer has expired. These executable binaries actually consist of a single inode, i.e. /usr/sbin/automountd and /usr/sbin/autounmountd are hardlinks to /usr/sbin/automount, and they do what they do by checking argv[0] in its main(). 3. etc/auto_master and etc/autofs/* etc/auto_master is a configuration file which describes relations between autofs(5) mount points and target filesystems to auto mount. As mentioned above, automountd(8) mounts filesystems based on this file. The auto_master(5) man page explains details of the format. etc/autofs/* are collection of scripts used by auto_master(5) when pre-defined special mappings are used. These are just copied from FreeBSD unless a script contains FreeBSD specific stuff (e.g. etc/autofs/special_media uses FreeBSD specific sysctl). 4. usr.sbin/fstyp Fstyp(8) is an utility to detect filesystem type of the given block device, and was originally added to FreeBSD for autofs. It's been used by automountd(8) to detect filesystem type of a block device when automountd(5) tries to mount a local filesystem (i.e. not NFS) by checking its signature. See "-media" mapping section in auto_master(5) for details. Fstyp(8) supports filesystems such as UFS, ext2, ISO9660, FAT, NTFS. FreeBSD version also supports ZFS, and DragonFlyBSD version supports HAMMER, but these two are dropped in OpenBSD, basically due to not being supported in OpenBSD (lacks library and header files defining ondisk format). --- Changes to the existing C code 1. Add MNT_AUTOMOUNTED, MOUNT_AUTOFS, struct autofs_args, etc to sys/sys/mount.h. MNT_AUTOMOUNTED flag allows VFS to recognize auto mounted filesystems (i.e. not the autofs(5) itself, but filesystems mounted by automountd(8)). Filesystems mounted with this flag set are shown as "automounted" in mount(8) output. 2. Add VT_AUTOFS to sys/sys/vnode.h. 3. Add MOPT_AUTOMOUNTED to sbin/mount. 4. Add cdev_autofs_init() to sys/sys/conf.h. 5. Add autofs to cdevsw[] in sys/arch/amd64/amd64/conf.c. 6. Add autofs to vfsconflist[] in sys/kern/vfs_init.c. 7. Add autofs to vfsinit() in sbin/sysctl/sysctl.c. 8. Add -E option to usr.bin/showmount/showmount.c. This is used by "-hosts" map of autofs which is etc/autofs/special_hosts. This option originate FreeBSD. 9. Add EVFILT_FS event for kqueue(2) in sys/sys/event.h and sys/kern/kern_event.c, which gets triggered on mount and unmount of any filesystem. This is needed by autounmountd(8) daemon. EVFILT_FS has existed in FreeBSD for a long time, but not in OpenBSD. --- Notes 1. Autofs(5) is currently only enabled on amd64, i.e. sys/arch/amd64/* and etc/etc.amd64/MAKEDEV, which is the arch used to port autofs. 2. "xxx first appeared in OpenBSD <version>" in newly added man pages have "6.x" for <version> at the moment. There are 6 new man pages, autofs(5), auto_master(5), automount(8), automountd(8), autounmountd(8) and fstyp(8) which originate FreeBSD. 3. The "-media" map is currently unsupported due to etc/autofs/special_media not being functional. The same script in FreeBSD uses GEOM sysctl, whereas there seems to be no easy way to achieve the same result on OpenBSD. See the bottom part of etc/autofs/special_media for details. I'd apply if this is doable on OpenBSD, which is to list all possible block devices and partitions for fstyp to check filesystem type.
