Re: [B2-devel] Preventing double-mounts

[Charles S. <bas...@ch...>]

On Jun 25, 2012, at 12:30 PM, Dave Vasilevsky wrote:

> On Sun, Jun 24, 2012 at 3:46 PM, Charles Srstka
> <bas...@ch...> wrote:
>> You can do this
>> by passing O_EXLOCK to the open() function. If you want open() to fail
>> immediately if the file is already open instead of simply blocking until the
>> file is available, then pass O_NONBLOCK as well.
> 
> What's the advantage of this over the flock(2) advisory locks I
> proposed? As far as I can tell they have the exact same behaviour on
> Mac OS X, but flock() is cross-platform and will work on Linux and BSD
> as well.
> 
> -V

They’re both equivalent; I believe that O_EXLOCK uses the advisory locks under the hood. I was thinking of a Mac-specific solution, since the posts I replied to were considered doing very Mac-specific IOKit things anyway. At the time I wrote that, your e-mail hadn’t posted to the list yet.

I would think that images becoming mounted while SheepShaver is running would be less of a concern on other platforms which can’t normally mount Mac volumes, though.

Charles