[PATCH 0/2] eventfd: simplify signal helpers

Alex Williamson alex.williamson at redhat.com
Tue Jul 18 08:52:03 AEST 2023

On Mon, 17 Jul 2023 19:12:16 -0300
Jason Gunthorpe <jgg at ziepe.ca> wrote:

> On Mon, Jul 17, 2023 at 01:08:31PM -0600, Alex Williamson wrote:
> > What would that mechanism be?  We've been iterating on getting the
> > serialization and buffering correct, but I don't know of another means
> > that combines the notification with a value, so we'd likely end up with
> > an eventfd only for notification and a separate ring buffer for
> > notification values.  
> All FDs do this. You just have to make a FD with custom
> file_operations that does what this wants. The uAPI shouldn't be able
> to tell if the FD is backing it with an eventfd or otherwise. Have the
> kernel return the FD instead of accepting it. Follow the basic design
> of eg mlx5vf_save_fops

Sure, userspace could poll on any fd and read a value from it, but at
that point we're essentially duplicating a lot of what eventfd provides
for a minor(?) semantic difference over how the counter value is
interpreted.  Using an actual eventfd allows the ACPI notification to
work as just another interrupt index within the existing vfio IRQ uAPI.


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