On Sun, Feb 18, 2024 at 08:11:58AM +0100, Greg KH wrote:

On Sat, Feb 17, 2024 at 10:03:35AM -0800, Saurabh Sengar wrote:

quoted

Add a function to query for the preferred ring buffer size of VMBus
device.

That says what you did, but not why you did it.

I thought subsequent patch will make it clear, but I can add more
info in cover letter. I will enhance this commit as well.

quoted

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
---
 drivers/hv/channel_mgmt.c | 7 +++++--
 drivers/hv/hyperv_vmbus.h | 5 +++++
 include/linux/hyperv.h    | 1 +
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 2f4d09ce027a..7ea444d72f9f 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c

@@ -120,7 +120,8 @@ const struct vmbus_device vmbus_devs[] = {
 	},
 
 	/* File copy */
-	{ .dev_type = HV_FCOPY,
+	{ .pref_ring_size = 0x4000,
+	  .dev_type = HV_FCOPY,
 	  HV_FCOPY_GUID,
 	  .perf_device = false,
 	  .allowed_in_isolated = false,

@@ -141,11 +142,13 @@ const struct vmbus_device vmbus_devs[] = {
 	},
 
 	/* Unknown GUID */
-	{ .dev_type = HV_UNKNOWN,
+	{ .pref_ring_size = 0x11000,
+	  .dev_type = HV_UNKNOWN,

Where do these magic numbers for the size come from?

This value is (16 + 1) page_size, which is found sufficient for most
of the slow devices. 16 page_size is for the ringbuffer and 1 page_size
for the headre. This is the approximation for default case, to avoid
using fall back case of 512 page_size as used by uio_hv_generic.

quoted

 	  .perf_device = false,
 	  .allowed_in_isolated = false,> >  	},
 };
+EXPORT_SYMBOL_GPL(vmbus_devs);
 
 static const struct {
 	guid_t guid;

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index f6b1e710f805..76ac5185a01a 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h

@@ -417,6 +417,11 @@ static inline bool hv_is_perf_channel(struct vmbus_channel *channel)
 	return vmbus_devs[channel->device_id].perf_device;
 }
 
+static inline size_t hv_dev_ring_size(struct vmbus_channel *channel)
+{
+	return vmbus_devs[channel->device_id].pref_ring_size;
+}
+
 static inline bool hv_is_allocated_cpu(unsigned int cpu)
 {
 	struct vmbus_channel *channel, *sc;

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 2b00faf98017..5951c7bb5712 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h

@@ -800,6 +800,7 @@ struct vmbus_requestor {
 #define VMBUS_RQST_RESET (U64_MAX - 3)
 
 struct vmbus_device {
+	size_t pref_ring_size;

No documentation for this?  What is the size in units of?

I can add a comment here like below:

/* 
 * Total memory in bytes allocated for the one complete ring buffer,
 * which includes the ring buffer header, of size PAGE_SIZE. This value
 * should be aligned to page_size.
 */

- Saurabh

thanks,

greg k-h