Re: [PATCH v3 4/5] blkmap: store type of blkmap device in corresponding structure

[Tobias Waldekranz <tobias@waldekranz.com>]

On mån, jan 20, 2025 at 16:20, Sughosh Ganu <sughosh.ganu@linaro.org> wrote:
> Add information about the type of blkmap device in the blkmap
> structure. Currently, the blkmap device is used for mapping to either
> a memory based block device, or another block device (linear
> mapping). Put information in the blkmap structure to identify if it is
> associated with a memory or linear mapped device. Which can then be
> used to take specific action based on the type of blkmap device.

Is this restriction really necessary? Why should it not be possible to
setup a block map like this:

 myblkmap:
.--------.      .-----.
| slice0 +------> RAM |
:--------:      '-----'     .-------.
| slice1 +------------------> eMMC0 |
:--------:      .-------.   '-------'
| slice2 +------> eMMC1 |
'........'      '-------'

Linux's "device mapper", after which blkmaps are modeled, works in this
way.  I.e. a blkmap is just a collection of slices, and it is up to each
slice how its data is provided, meaning that the user is free to compose
their virtual block device in whatever way they need.

Looking at the pmem patch that follows this one, I am not able to find
anything that would motivate restricting the functionality either.