Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem()

[Jason Gunthorpe]

On Tue, Jul 05, 2022 at 09:51:08AM +0200, Christoph Hellwig wrote:

> But what also really matters here:  I don't want every user that
> wants to be able to mmap a character device to do all this work.
> The layering is simply wrong, it needs some character device
> based helpers, not be open code everywhere.

I think alot (all?) cases would be happy if the inode was 1:1 with the
cdev struct device. I suppose the cdev code would still have to create
pseudo fs, but at least that is hidden.

> In fact I'm not even sure this should be a character device, it seems
> to fit it way better with the PCI sysfs hierchacy, just like how we
> map MMIO resources, which these are anyway.  And once it is on sysfs
> we do have a uniqueue inode and need none of the pseudofs stuff, and
> don't need all the glue code in nvme either.

Shouldn't there be an allocator here? It feels a bit weird that the
entire CMB is given to a single process, it is a sharable resource,
isn't it?

Jason