Re: mount race prevention

[Crystal Kolipe <kolipe.c%exoticsilicon.com@localhost>]

On Tue, Nov 18, 2025 at 07:36:11PM +0100, Edgar Fu wrote:
> > So, my first question would be, what precisely is it you're trying to
> > prevent?
> I want to prevent B to mount something on a temporary mount point already 
> in use by A. I.e., A sees the mount point is free, B sees it's free, 
> A mounts, B mounts, and A operates on the wrong thing.
> 
> I have scripts that operate on snapshots they take. I.e., when I backup 
> /export/home, I look for an unused fss device, take an ffs snapshot of 
> /dev/dk5 on it, mount it, backup it, unmount, fssconfig -u.
> The problem is I need a temporary mount point like /mnt which (highly 
> unlikely) could be in use by another (incarnation of the same) script.
> Yes, I guess I could be using temporary entries in /tmp.

In this case I would probably create a dedicated directory such as
/mnt_myscript, and for each invokation of the script have it always create a
unique random mount point under that directory, use it for the duration of
that particular run, then unlink it.

I.E. never use /mnt_myscript directly, but only as a place to create a
temporary mountpoint.

Assuming that there are no other file sharing or locking issues, that
potentially also allows multiple copies of the script to run simultaneously
instead of erroring out.