linux-kernel - Re: [PATCH 1/2] eventfd: reorganize the code to simplify new flags

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Date:	Thu, 27 Aug 2009 14:58:24 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Paolo Bonzini <bonzini@....org>
Cc:	davidel@...ilserver.org, avi@...hat.com, gleb@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] eventfd: reorganize the code to simplify new flags

On Thu, Aug 27, 2009 at 01:48:53PM +0200, Paolo Bonzini wrote:
> On 08/20/2009 05:57 PM, Michael S. Tsirkin wrote:
>> +static inline int eventfd_writeable(struct eventfd_ctx *ctx, u64 n)
>> +{
>> +	return ULLONG_MAX - n>  ctx->count;
>> +}
>> +
>> +static inline void eventfd_dowrite(struct eventfd_ctx *ctx, u64 ucnt)
>> +{
>> +	if (eventfd_writeable(ctx, ucnt))
>> +		ucnt = ULLONG_MAX - ctx->count;
>> +
>> +	ctx->count += ucnt;
>
> In any case, this usage of eventfd_writeable is wrong: the code was like  
> this:
>
> -	if (ULLONG_MAX - ctx->count < n)
> -		n = (int) (ULLONG_MAX - ctx->count);
> -	ctx->count += n;
> +	eventfd_dowrite(ctx, n);
>
> and so it should be !eventfd_writable.  (This smelled when I was editing  
> patch 2, so I went back and checked patch 1).
>
> Paolo

Right, patch 2 actually fixed this back.  The best thing is to open-code
it actually, since we handle it in a way that only applies to a counter,
anyway.  Will post a fixed v1.

-- 
MST
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