The various forms of allocating a netdevice.

From include/linux/netdevice.h, optional private data is stored (aligned) after the end of the structure:

static inline void *netdev_priv(const struct net_device *dev)
{
	return (char *)dev + ALIGN(sizeof(struct net_device), NETDEV_ALIGN);
}

#define	NETDEV_ALIGN		32

Explanation of NETDEV_ALIGN here.

The base allocation routine from net/core/dev.c for allocating a single device:

/**
 * alloc_netdev_mqs - allocate network device
 * @sizeof_priv: size of private data to allocate space for
 * @name: device name format string
 * @name_assign_type: origin of device name
 * @setup: callback to initialize device
 * @txqs: the number of TX subqueues to allocate
 * @rxqs: the number of RX subqueues to allocate
 *
 * Allocates a struct net_device with private data area for driver use
 * and performs basic initialization.  Also allocates subqueue structs
 * for each queue on the device.
 */
struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
		unsigned char name_assign_type,
		void (*setup)(struct net_device *),
		unsigned int txqs, unsigned int rxqs)
{
	struct net_device *dev;
	unsigned int alloc_size;
	struct net_device *p;

	BUG_ON(strlen(name) >= sizeof(dev->name));

	if (txqs < 1) {
		pr_err("alloc_netdev: Unable to allocate device with zero queues\n");
		return NULL;
	}

	if (rxqs < 1) {
		pr_err("alloc_netdev: Unable to allocate device with zero RX queues\n");
		return NULL;
	}

	alloc_size = sizeof(struct net_device);
	if (sizeof_priv) {
		/* ensure 32-byte alignment of private area */
		alloc_size = ALIGN(alloc_size, NETDEV_ALIGN);
		alloc_size += sizeof_priv;
	}
	/* ensure 32-byte alignment of whole construct */
	alloc_size += NETDEV_ALIGN - 1;

	p = kvzalloc(alloc_size, GFP_KERNEL | __GFP_RETRY_MAYFAIL);
	if (!p)
		return NULL;
        ... snip ...

Not a lot of drivers call this routine directly given that you can call more convenient wrappers (see below).

From include/linux/netdevice.h:

#define alloc_netdev(sizeof_priv, name, name_assign_type, setup) \
	alloc_netdev_mqs(sizeof_priv, name, name_assign_type, setup, 1, 1)

#define alloc_netdev_mq(sizeof_priv, name, name_assign_type, setup, count) \
	alloc_netdev_mqs(sizeof_priv, name, name_assign_type, setup, count, \
			 count)

From include/linux/etherdevice.h:

struct net_device *alloc_etherdev_mqs(int sizeof_priv, unsigned int txqs,
					    unsigned int rxqs);
#define alloc_etherdev(sizeof_priv) alloc_etherdev_mq(sizeof_priv, 1)
#define alloc_etherdev_mq(sizeof_priv, count) alloc_etherdev_mqs(sizeof_priv, count, count)

From net/ethernet/net.c:

struct net_device *alloc_etherdev_mqs(int sizeof_priv, unsigned int txqs,
				      unsigned int rxqs)
{
	return alloc_netdev_mqs(sizeof_priv, "eth%d", NET_NAME_UNKNOWN,
				ether_setup, txqs, rxqs);
}

From include/linux/etherdevice.h:

struct net_device *devm_alloc_etherdev_mqs(struct device *dev, int sizeof_priv,
					   unsigned int txqs,
					   unsigned int rxqs);
#define devm_alloc_etherdev(dev, sizeof_priv) devm_alloc_etherdev_mqs(dev, sizeof_priv, 1, 1)

From net/ethernet/net.c:

struct net_device *devm_alloc_etherdev_mqs(struct device *dev, int sizeof_priv,
					   unsigned int txqs, unsigned int rxqs)
{
	struct net_device **dr;
	struct net_device *netdev;

	dr = devres_alloc(devm_free_netdev, sizeof(*dr), GFP_KERNEL);
	if (!dr)
		return NULL;

	netdev = alloc_etherdev_mqs(sizeof_priv, txqs, rxqs);
	if (!netdev) {
		devres_free(dr);
		return NULL;
	}

	*dr = netdev;
	devres_add(dev, dr);

	return netdev;
}