linux-kernel - Re: [PATCH 2/7] kfifo: move out spinlock

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Date:	Mon, 17 Aug 2009 09:08:29 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Stefani Seibold <stefani@...bold.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Andi Kleen <andi@...stfloor.org>,
	Amerigo Wang <xiyou.wangcong@...il.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH 2/7] kfifo: move out spinlock

> > Those wrappers happen to be called kfifo_get and kfifo_put
> 
> Those names are wrong.

We've had them for years

> They're wrong because they are the spinlock-specific variant.  What are
> we going to call the mutex_lock-specific variant?

There isn't one.

> 
> > > But the happens-to-use-spin_lock functions shouldn't be called
> > > kfifo_get(), because that steals namespace from the unlocked functions,
> > > and makes the naming for the happens-to-use-mutex_lock functions look
> > > weird.
> > 
> > All over the kernel unlocked function versions have a leading _ name.
> > It's the kernel convention.
> 
> tisn't.  radix-tree, rbrtee, idr, list_head, prio_tree, flex_array -
> none of them use that convention.

Some random "10 second grep" examples, and this is also used more
generally for the "without extra goo" variant of things

__set_special_pids
__sysrq_put_key_op
__sysrq_get_key_op
__handle_sysrq
__audit_getname
__audit_inode
__audit_node_child

and the without extra goo use includes such minor classics
__get_user
__put_user

the kernel contains lots and lots of

__foo()

foo()
{
	spin_lock(bar);
	__foo()
	spin_unlock(bar)
}

> > The other thing I must say I dislike about these patches is the
> > gratuitious 'let's rename all the functions' approach it takes. The kfifo
> > API is documented, used and random API of the year type changes mess
> > stuff up and cause unneeded churn.
> 
> It fixes naming mistakes.  Long-term it is the correct thing to do. 
> Best to do it now before we get more callers.

Why don't we fix all the really dumb naming mistakes then - things like
the chrdev interfaces ? Massive churn, massive confusion. Patches are
always being rejected (and rightfully so) for causing such messes.

And remember: its very hard to fix existing API documentation and books.
It's doubly dangerous (and IMHO a complete no-no) to change the API of an
interface if you don't change it such that old code will not reliably get
a compile time failure.

Alan
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