[dm-devel] [PATCH] dm-bufio: prefetch

[Alasdair G Kergon]

Let's move this 'found_buffer' code after both places that use it, I think.
(goto an earlier point in the function would normally mean a loop, which
this isn't)

Alasdair


On Tue, Mar 13, 2012 at 10:46:00AM -0400, Mikulas Patocka wrote:
> @@ -882,6 +888,19 @@ static struct dm_buffer *__bufio_new(str
>  
>  	b = __find(c, block);
>  	if (b) {
> +found_buffer:
> +		if (nf == NF_PREFETCH)
> +			return NULL;
> +		/*
> +		 * Note: it is essential that we don't wait for the buffer to be
> +		 * read if dm_bufio_get function is used. Both dm_bufio_get and
> +		 * dm_bufio_prefetch can be used in the driver request routine.
> +		 * If the user called both dm_bufio_prefetch and dm_bufio_get on
> +		 * the same buffer, it would deadlock if we waited.
> +		 */
> +		if (nf == NF_GET && unlikely(test_bit(B_READING, &b->state)))
> +			return NULL;
> +
>  		b->hold_count++;
>  		__relink_lru(b, test_bit(B_DIRTY, &b->state) ||
>  			     test_bit(B_WRITING, &b->state));

> @@ -900,10 +921,7 @@ static struct dm_buffer *__bufio_new(str
>  	b = __find(c, block);
>  	if (b) {
>  		__free_buffer_wake(new_b);
> -		b->hold_count++;
> -		__relink_lru(b, test_bit(B_DIRTY, &b->state) ||
> -			     test_bit(B_WRITING, &b->state));
> -		return b;
> +		goto found_buffer;
>  	}