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

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Date:	Thu, 27 Aug 2009 13:48:53 +0200
From:	Paolo Bonzini <bonzini@....org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
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 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
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