Re: [PATCH] the dm-loop target

Christoph Hellwig
2025-03-03T17:24:52Z

On Mon, Mar 03, 2025 at 05:06:16PM +0100, Heinz Mauelshagen wrote:
> On Mon, Mar 3, 2025 at 4:24 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> > On Mon, Mar 03, 2025 at 03:57:23PM +0100, Heinz Mauelshagen wrote:
> > > dm-loop avoids the file system abstraction, thus gains the resulting
> > > performance advantage versus the loop driver.
> >
> > How?
> >
>
> It uses a predefined map and thus avoids VFS -> FS write path overhead
> completelly.

But you simply can't use a "pre-defined map". It's fundamentally
unsafe.

> The inode fiemap() operation would avoid issues relative to outdated bmap().

No, using that for I/O is even worse.