int ibv_query_device(struct ibv_context *context,
                     struct ibv_device_attr *device_attr);

Description

ibv_query_device() returns the attributes of an RDMA device that is associated with a context.

Here is the full description of struct ibv_device_attr:

The RDMA device attributes, returned by ibv_query_device(), are constant and won't be changed by the device or by the SM, thus a program can call to this verb and save those attributes for later use.

The maximum values returned by ibv_query_device() are the upper limits of supported resources of the device. However, it may not be possible to use these maximum values since the actual number of any resource that can be created may be limited by the machine configuration, the amount of host memory, user permissions, and the amount of resources already in use by other users/processes.

Parameters

Return Values

Examples

Query a device attributes:

struct ibv_device_attr device_attr;
int rc;
 
rc = ibv_query_device(ctx, &device_attr);
if (rc) {
	fprintf(stderr, "Error, failed to query the device '%s' attributes\n",
		ibv_get_device_name(device_list[i]));
	return -1;
}

show_devices_attr.c

FAQs

ibv_query_device() indicated that I can create X elements from a resource, but I was able to create only Y (where Y is less than X), is this is o.k.?

Yes, this may happen since the values reported by ibv_query_device() are the upper limits supported by the device. If any other processes/modules created elements from this resource too, the available number this resource was decreased.

Can I know how many elements of a resource are available for me to create?

No, you can't. This value depends on a lot of factors.

Can I know how many elements of a resource were created by other processes/modules?

No, you can't. Currently, the RDMA stack doesn't support this feature.

Written by: Dotan Barak on July 13, 2012.on February 17, 2015.