Re: [PATCH 2/6] uio_hv_generic: Query the ringbuffer size for device

Greg KH
2024-02-19T08:50:58Z

On Sat, Feb 17, 2024 at 10:03:36AM -0800, Saurabh Sengar wrote:
> Query the ring buffer size from pre defined table per device.
> Keep the size as is if the device doesn't have any preferred
> ring size.

What is the "as is" size?

>
> Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> ---
> drivers/uio/uio_hv_generic.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/uio/uio_hv_generic.c b/drivers/uio/uio_hv_generic.c
> index 20d9762331bd..4bda6b52e49e 100644
> --- a/drivers/uio/uio_hv_generic.c
> +++ b/drivers/uio/uio_hv_generic.c
> @@ -238,6 +238,7 @@ hv_uio_probe(struct hv_device *dev,
> struct hv_uio_private_data *pdata;
> void *ring_buffer;
> int ret;
> + size_t ring_size = hv_dev_ring_size(channel);
>
> /* Communicating with host has to be via shared memory not hypercall */
> if (!channel->offermsg.monitor_allocated) {
> @@ -245,12 +246,14 @@ hv_uio_probe(struct hv_device *dev,
> return -ENOTSUPP;
> }
>
> + if (!ring_size)
> + ring_size = HV_RING_SIZE * PAGE_SIZE;

Why the magic * PAGE_SIZE here?

Where is it documented that ring_size is in pages?

And what happens when PAGE_SIZE is changed? Why are you relying on that
arbritrary value to dictate your buffer sizes to a device that has
no relationship with PAGE_SIZE?

Yes, I know you are copying what was there today, but you have the
chance to rethink and most importantly, DOCUMENT this decision properly
now.

thanks,

greg k-h