linux kernel - not understand the mechanism of free_netdev -

i study network-device-driver recently. somehow not understand free_netdev function.

i have read following link: possible de-reference of private data using net_device

the answer says when free network device, private data free.

after checking function, found call following function:

 void netdev_freemem(struct net_device *dev)  {      char *addr = (char *)dev - dev->padded;       kvfree(addr);  } 

but cannot understand why call function free net_device memory, , private data?

or understanding wrong...

just wondering if can guide me understand mechanism of free_netdev.

thanks in advance.

check out alloc_netdev() function definition in net/core/dev.c

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 = kzalloc(alloc_size, gfp_kernel | __gfp_nowarn | __gfp_repeat);     if (!p)      p = vzalloc(alloc_size); if (!p)      return null;  dev = ptr_align(p, netdev_align); dev->padded = (char *)dev - (char *)p;  

it kzalloc of sizeof(struct net_device) + sizeof_priv + padding_bytes.

so net_device private memory following struct net_device , hence kfree() of netdev frees net_device_private memory.