Re: [PATCH] the dm-loop target

Christoph Hellwig
2025-03-04T13:49:53Z

On Mon, Mar 03, 2025 at 10:03:42PM +0100, Mikulas Patocka wrote:
> Swapfile does ahead of time mapping.

It does. But it is:

a) protected against modification by the S_SWAPFILE flag and checked
for full allocation first
b) something we want to get rid of because even with the above it is
rather problematic

> And I just looked at what swapfile
> does and copied the logic into dm-loop. If swapfile is not broken, how
> could dm-loop be broken?

As said above, swapfile works around the brokenness in ways that you
can't. And just blindly copying old code without understanding it is
never a good idea.

>
> > > Would Jens Axboe agree to merge the dm-loop logic into the existing loop
> > > driver?
> >
> > What logic?
>
> The ahead-of-time mapping.

As said multiple times you can't do that. The block mapping is
file system private information.