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Date: Thu, 16 May 2013 11:24:01 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] qemu-io: Fix 'map' output
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: qemu-devel@nongnu.org

Am 16.05.2013 um 11:14 hat Stefan Hajnoczi geschrieben:
> On Wed, May 15, 2013 at 01:47:12PM +0200, Kevin Wolf wrote:
> > +static int map_is_allocated(int64_t sector_num, int64_t nb_sectors, int64_t *pnum)
> > +{
> > +    int num, num_checked;
> > +    int ret, firstret;
> > +
> > +    num_checked = MIN(nb_sectors, INT_MAX);
> > +    ret = bdrv_is_allocated(bs, sector_num, num_checked, &num);
> > +    if (ret < 0) {
> > +        return ret;
> > +    }
> > +
> > +    firstret = ret;
> > +    *pnum = num;
> > +
> > +    while (nb_sectors > 0 && ret == firstret) {
> > +        sector_num += num;
> > +        nb_sectors -= num;
> > +
> > +        num_checked = MIN(nb_sectors, INT_MAX);
> > +        ret = bdrv_is_allocated(bs, sector_num, num_checked, &num);
> > +        if (ret == firstret) {
> > +            *pnum += num;
> > +        } else {
> > +            break;
> > +        }
> 
> The break makes && ret == firstret redundant above.  I suggest just
> while (nb_sectors > 0) { ... } which is easier to read.

Okay. I wasn't sure which was better. Don't know though how it came that
I have both checks now...

> Also, if you respin the patch please tweak the commit message.
> "Coalesce 'map' output" is more specific than "Fix 'map' output" -
> unless this really fixes a bug which you didn't mention in the commit
> description.

I'll change the title. It makes different formats behave the same even
if they work in different granularities. I think QED was bitten by this
in qemu-iotests somwhere because it could give different results than
qcow2, possibly also dependent on timing. Maybe I should mention that as
well in the commit message.

Kevin