Network interface synchronization docs

[Jeff Garzik]

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I just updated Documentation/networking/netdevices.txt locally to the 
attached file, which describes the synchronization rules for net drivers 
in the 2.4.x and 2.5.x kernels.  (Astute readers will notice a striking 
similarity to 2.2.x locking rules as well)

Comments and corrections to the attached doc requested.  I realize it's 
not much right now, but this is core info I want to make sure is 
correct, and that everyone agrees on.

Thanks to Robert Olsson for a pointer about dev->poll().

Future notes:  this doc will hopefully expand in time to describe not 
only the netdevice API but also standard ethernet and net driver 
practices.  Patches welcome!

	Jeff

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Network Devices, the Kernel, and You!

Introduction
============
The following is a random collection of documentation regarding
network devices.

struct net_device synchronization rules
=======================================
dev->open:
	Synchronization: rtnl_lock() semaphore.
	Context: process

dev->stop:
	Synchronization: rtnl_lock() semaphore.
	Context: process
	Notes: netif_running() is guaranteed false when this is called

dev->do_ioctl:
	Synchronization: rtnl_lock() semaphore.
	Context: process

dev->get_stats:
	Synchronization: dev_base_lock rwlock.
	Context: nominally process, but don't sleep inside an rwlock

dev->hard_start_xmit:
	Synchronization: dev->xmit_lock spinlock.
	Context: BHs disabled

dev->tx_timeout:
	Synchronization: dev->xmit_lock spinlock.
	Context: BHs disabled

dev->set_multicast_list:
	Synchronization: dev->xmit_lock spinlock.
	Context: BHs disabled

dev->poll:
	Synchronization: __LINK_STATE_RX_SCHED bit in dev->state.  See
		dev_close code and comments in net/core/dev.c for more info.
	Context: softirq

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