Re: Remount read-only and fstrans

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

> Date: Sun, 19 Feb 2017 11:15:54 +0100
> From: "J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>
> 
> Plan is to suspend the file system while the mounted file system
> gets updated.  This way no operations run on the mounted file
> system during update and all operations see the state before or
> after the update.
> [...]
> Plan is to move fstrans_start()/fstrans_done() into vnode_if.c and
> enable vfs_suspend() on all file systems.

This sounds like a great plan!  It is essentially what I have had in
mind for several years now but never found the time to implement.
Please do it!

I wonder whether the FSTRANS=NO operations should also include some
kind of KASSERT to guarantee the caller has arranged, in some other
way, that the mount point is not going away.

If you can write a brief summary of the API changes, I'd be happy to
merge them into the fstrans(9) man page, if you're not doing so
already.