MC_GETPROP(9E) Driver Entry Points MC_GETPROP(9E)

mc_getprop
get device properties

#include <sys/mac_provider.h>

int
prefix_m_getprop(void *driver, const char *pr_name, mac_prop_id_t pr_num, uint_t pr_valsize, void *pr_val);

illumos DDI specific

driver
A pointer to the driver's private data that was passed in via the m_pdata member of the mac_register(9S) structure to the mac_register(9F) function.
pr_name
A null-terminated string that contains the name of the property.
pr_num
A constant that is used to identify the property.
pr_valsize
A value that indicates the size in bytes of pr_val.
pr_val
A pointer to a pr_valsize byte buffer that can store the property.

The mc_getprop() entry point is used to obtain the value of a given device's property and place it into pr_val.

When the mc_getprop() entry point is called, the driver needs to first identify the property. The set of possible properties and their meaning is listed in the PROPERTIES section of mac(9E). It should identify the property based on the value of pr_num. Most drivers will use a switch statement and for any property that it supports it should then check if the value in pr_valsize is sufficient for the property, comparing it to the minimum size listed for the property in mac(9E). If it is not, then it should return an error. Otherwise, it should copy the property's value into pr_val. When an unknown or unsupported property is encountered, generally the default case of the switch statement, the device driver should return an error.

The special property MAC_PROP_PRIVATE indicates that this is a device driver specific private property. The device driver must then look at the value of the pr_name argument and use strcmp(9F) on it, comparing it to each of its private (bounded-size) properties to identify which one it is.

At this time, private properties are limited to being string based properties. If other types of property values are used, they will not be rendered correctly by dladm(1M).

The device driver can access its device soft state by casting the device pointer to the appropriate structure. As this may be called while other operations are ongoing, the device driver should employ the appropriate locking while reading the properties.

The mc_getprop() function is generally called from kernel context.

Upon successful completion, the device driver should have copied the value of the property into pr_val and return 0. Otherwise, a positive error should be returned to indicate failure.

The following example shows how a device driver might structure its mc_getprop() entry point.
#include <sys/mac_provider.h>

/*
 * Note, this example merely shows the structure of this function.
 * Different devices will manage their state in different ways. Like other
 * examples, this assumes that the device has state in a structure called
 * example_t and that there is a lock which keeps track of that state.
 */
static char *example_priv_props[] = {
	"_rx_intr_throttle",
	"_tx_intr_throttle",
	NULL
};

static int
example_m_getprop_private(example_t *ep, const char *pr_name, uint_t pr_valsize,
    void *pr_val)
{
	uint32_t val;

	ASSERT(MUTEX_HELD(&ep->ep_lock));
	if (strcmp(pr_name, example_priv_props[0] == 0) {
		val = ep->ep_rx_itr;
	} else if (strcmp(pr_name, example_priv_props[1] == 0) {
		val = ep->ep_tx_itr;
	} else {
		return (ENOTSUP);
	}

	/*
	 * Due to issues in the GLDv3, these must be returned as string
	 * properties.
	 */
	if (snprintf(pr_val, pr_valsize, "%d", val) >= pr_valsize)
		return (EOVERFLOW);

	return (0);
}

static int
example_m_getprop(void *arg, const char *pr_name, mac_prop_id_t pr_num,
    uint_t pr_valsize, void *pr_val)
{
	int ret = 0;
	uint64_t speed;
	example_t *ep = arg;

	mutex_enter(&ep->ep_lock);

	/*
	 * This only handles a subset of the properties that exist on the
	 * system. A proper driver will need to handle more. See mac(9E) for a
	 * full property list.
	 */
	switch (pr_num) {
	case MAC_PROP_DUPLEX:
		if (pr_valsize < sizeof (link_duplex_t)) {
			ret = EOVERFLOW;
			break;
		}
		bcopy(ep->ep_link_duplex, pr_val, sizeof (link_duplex_t));
	case MAC_PROP_SPEED:
		if (pr_valsize < sizeof (uint64_t)) {
			ret = EOVERFLOW;
			break;
		}
		/*
		 * The link speed is stored in Mbits/s in this driver and is
		 * expected in bits/s.
		 */
		speed = ep->ep_link_speed * 1000000ULL;
		bcopy(&speed, pr_val, sizeof (speed));
		break;
	case MAC_PROP_MTU:
		if (pr_valsize < sizeof (uint32_t)) {
			ret = EOVERFLOW;
			break;
		}
		bcopy(&ep->ep_mtu, pr_val, sizeof (speed));
		break;
	case MAC_PROP_PRIVATE:
		ret = example_m_getprop_private(ep, pr_name, pr_valsize,
		    pr_val);
		break;
	default:
		ret = ENOTSUP;
		break;
	}

	mutex_exit(&ep->ep_lock);

	return (ret);
}

The device driver may return one of the following errors. While this list is not intended to be exhaustive, it is recommended to use one of these if possible.
This error should be used whenever an unknown or unsupported property is encountered.
This error should be used when pr_valsize is smaller than the required size for a given value.

mac(9E), mac_register(9F), strcmp(9F), mac_register(9S)
February 15, 2020 OmniOS