Re: [PATCH] the dm-loop target

Christoph Hellwig
2025-03-03T17:24:15Z

On Mon, Mar 03, 2025 at 05:16:48PM +0100, Mikulas Patocka wrote:
> What should I use instead of bmap? Is fiemap exported for use in the
> kernel?

You can't do an ahead of time mapping. It's a broken concept.

> Would Jens Axboe agree to merge the dm-loop logic into the existing loop
> driver?

What logic?

> Dm-loop is significantly faster than the regular loop:
>
> # modprobe brd rd_size=1048576
> # dd if=/dev/zero of=/dev/ram0 bs=1048576
> # mkfs.ext4 /dev/ram0
> # mount -t ext4 /dev/ram0 /mnt/test
> # dd if=/dev/zero of=/mnt/test/test bs=1048576 count=512

All of this needs to be in a commit log. Also note that the above:

a) does not use direct I/O which any sane loop user should
b) is not on a file but a block device, rendering the use of a loop
device entirely pointless.