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

[Sagi Grimberg]

On 23/10/2024 8:24, Christoph Hellwig wrote:
> On Tue, Oct 22, 2024 at 08:53:47AM -0600, Keith Busch wrote:
> > You'd may want to know max_sectors_kb, dma_alignment, nr_requests,
> > virt_boundary_mask. Maybe some others.
> >
> > The request_queue is owned by the block layer, so that seems like an
> > okay place to export it, but attached to some other device's sysfs
> > directory instead of a gendisk.
> >
> > I'm just suggesting this because it doesn't sound like this is an nvme
> > specific problem.
> Well, it's a problem specific to passthrough without a gendisk, which is
> the NVMe admin queue and the /dev/sg device.  So it's common-ish :)
>
>
> Note that for the programs using passthrough sysfs isn't actually a very
> good interface, as finding the right directory is pain, as is opening,
> reading and parsing one ASCIII file per limit.
>
> One thing I've been wanting to do also for mkfs tools and similar is a
> generic extensible ioctl to dump all the queue limits.  That's a lot
> easier and faster for the tools and would work very well here.
>
> Note that we could still be adding new limits at any point of time
> (although I have a hard time thinking what limit we don't have yet),
> so we still can't guarantee that non-trivial I/O will always work.

Makes sense to me. Although people would still like to be able to
see this value outside of an application context. We can probably
extend nvme-cli to display this info...