Re: [dm-devel] [PATCH 2/2] dm thin: support for non power of 2 pool blocksize

[Joe Thornber <thornber redhat com>]

Hi Mike,

In general this looks good.  A lot cleaner now you've dropped the
specialisation of the division.  A few nit-picks below.

- Joe

On Sat, Apr 28, 2012 at 12:44:29AM -0400, Mike Snitzer wrote:
> +/*
> + * do_div wrappers that don't modify the dividend
> + */
> +static inline sector_t dm_thin_do_div(sector_t a, __u32 b)
> +{
> +	sector_t r = a;
> +
> +	do_div(r, b);
> +	return r;
> +}
> +
> +static inline sector_t dm_thin_do_mod(sector_t a, __u32 b)
> +{
> +	sector_t tmp = a;
> +
> +	return do_div(tmp, b);
> +}

Please don't inline static functions.  Let the compiler make the
decision.

Also those sector_t's are passed by value, so you don't need to
declare r or tmp.  eg, it's enough to do this:

static sector_t dm_thin_do_div(sector_t a, __u32 b)
{
	do_div(a, b);
	return a;
}

static sector_t dm_thin_do_mod(sector_t a, __u32 b)
{
	return do_div(a, b);
}

> @@ -1941,12 +1954,18 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)

...

> +	if (dm_thin_do_mod(ti->len, block_size)) {
> +		ti->error = "Data device is not a multiple of block size";
> +		r = -EINVAL;
> +		goto out;
> +	}

I don't see the need for this check.  If I have a disk that isn't a
multiple of the block size why should I have to layer a linear mapping
on it to truncate it before I can use it as a data volume?  Any
partial block at the end of the device is already ignored (see the
data_size calculation in pool_preresume).  Is this restriction causing
some of the changes you made to the test-suite?