[PATCH] nvme-sysfs: display max_hw_sectors_kb without requiring namespaces

[Keith Busch]

On Wed, Oct 16, 2024 at 09:31:08PM +0000, Abhishek Bapat wrote:
> max_hw_sectors based on DMA optimized limitation") introduced a
> limitation on the value of max_hw_sectors_kb, restricting it to 128KiB
> (MDTS = 5). This restricion was implemented to mitigate lockups
> encountered in high-core count AMD servers.

There are other limits that can constrain transfer sizes below the
device's MDTS. For example, the driver can only preallocate so much
space for DMA and SGL descriptors, so 8MB is the current max transfer
sizes the driver can support, and a device's MDTS can be much bigger
than that.

Anyway, yeah, I guess having a controller generic way to export this
sounds like a good idea, but I wonder if the nvme driver is the right
place to do it. The request_queue has all the limits you need to know
about, but these are only exported if a gendisk is attached to it.
Maybe we can create a queue subdirectory to the char dev too.