linux-kernel - Re: [PATCH 1/7] aoe: support more AoE addresses with dynamic block device minor numbers

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Date:	Tue, 2 Oct 2012 14:12:30 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ed Cashin <ecashin@...aid.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] aoe: support more AoE addresses with dynamic block
 device minor numbers

On Mon, 1 Oct 2012 18:59:12 -0700
Ed Cashin <ecashin@...aid.com> wrote:

> The ATA over Ethernet protocol uses a major (shelf) and
> minor (slot) address to identify a particular storage target.
> These changes remove an artificial limitation the aoe driver
> imposes on the use of AoE addresses.  For example, without these
> changes, the slot address has a maximum of 15, but users commonly
> use slot numbers much greater than that.
> 
> The AoE shelf and slot address space is often used sparsely.
> Instead of using a static mapping between AoE addresses and the
> block device minor number, the block device minor numbers are now
> allocated on demand.
> 
> ...

Very minor things...

>
> ...
>
> +static int
> +minor_get(ulong *minor)
>  {
> -	struct aoedev *d;
>  	ulong flags;
> +	ulong n;
> +	int error = 0;
> +
> +	spin_lock_irqsave(&used_minors_lock, flags);
> +	n = find_first_zero_bit(used_minors, N_DEVS);
> +	if (n < N_DEVS)
> +		set_bit(n, used_minors);
> +	else
> +		error = -1;
> +	spin_unlock_irqrestore(&used_minors_lock, flags);
> +
> +	*minor = n * AOE_PARTITIONS;
> +	return error;
> +}

- can use the more efficient __set_bit() inside that spinlock.

- could avoid setting *minor if we're returning an error.

> -	spin_lock_irqsave(&devlist_lock, flags);
> +static void
> +minor_free(ulong minor)
> +{
> +	ulong flags;
>  
> -	for (d=devlist; d; d=d->next)
> -		if (d->aoemajor == maj && d->aoeminor == min) {
> -			d->ref++;
> -			break;
> -		}
> +	minor /= AOE_PARTITIONS;
> +	BUG_ON(minor >= N_DEVS);
>  
> -	spin_unlock_irqrestore(&devlist_lock, flags);
> -	return d;
> +	spin_lock_irqsave(&used_minors_lock, flags);
> +	BUG_ON(!test_bit(minor, used_minors));
> +	clear_bit(minor, used_minors);
> +	spin_unlock_irqrestore(&used_minors_lock, flags);
>  }

Could use

	BUG_ON(!__test_and_clear_bit(...));

This will work, but I think it's bad form to put an expression with
side-effects inside an assert macro.


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