`getfsstat(2)` is used to retrieve the list of mounted file systems,
which libzfs uses when fetching properties like mountpoint, atime,
setuid, etc. The `mode` parameter may be `MNT_NOWAIT`, which uses
information in the VFS's cache, or `MNT_WAIT`, which effectively does a
`statfs` on every single mounted file system in order to fetch the most
up-to-date information. As far as I can tell, the only fields that
libzfs cares about are the filesystem's name, mountpoint, fstypename,
and mount flags. Those things are always updated on mount and unmount,
so they will always be accurate in the VFS's mount cache except in two
circumstances:
1) When a file system is busy unmounting
2) When a ZFS file system changes the value of a mount-overridable
property like atime or setuid, but doesn't remount the file system.
Right now that only happens when the property is changed by an
unprivileged user who has delegated authority to change the property
but not to mount the dataset. But perhaps libzfs could choose to do
it for other reasons in the future.
Switching to `MNT_NOWAIT` will greatly improve speed with no downside,
as long as we explicitly update the mount cache whenever we change a
mount-overridable property.
For comparison, Illumos gets this information using the native
`getmntany` and `getmntent` functions, which also use cached
information. The illumos function that would refresh the cache,
`resetmnttab`, is never called by libzfs.
And on GNU/Linux, `getmntany` and `getmntent` don't even communicate
with the kernel directly. They simply parse the file they are given,
which is usually /etc/mtab or /proc/mounts. Perhaps the implementation
of /proc/mounts is synchronous, ala MNT_WAIT; I don't know.
Sponsored-by: Axcient
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alan Somers <asomers@gmail.com>
Closes: #12091
Add the FreeBSD platform code to the OpenZFS repository. As of this
commit the source can be compiled and tested on FreeBSD 11 and 12.
Subsequent commits are now required to compile on FreeBSD and Linux.
Additionally, they must pass the ZFS Test Suite on FreeBSD which is
being run by the CI. As of this commit 1230 tests pass on FreeBSD
and there are no unexpected failures.
Reviewed-by: Sean Eric Fagan <sef@ixsystems.com>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes#898Closes#8987
Alan Somers
Matthew Macy