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Re: [Qemu-devel] [RFC PATCH v2 03/23] qcow2: Change handle_dependency to
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [RFC PATCH v2 03/23] qcow2: Change handle_dependency to byte granularity |
Date: |
Fri, 15 Feb 2013 10:12:35 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, Feb 14, 2013 at 04:45:06PM +0100, Kevin Wolf wrote:
> On Thu, Feb 14, 2013 at 03:48:51PM +0100, Stefan Hajnoczi wrote:
> > On Wed, Feb 13, 2013 at 02:21:53PM +0100, Kevin Wolf wrote:
> > > + *
> > > + * -EAGAIN if we had to wait for another request, previously gathered
> > > + * information on cluster allocation may be invalid now. The
> > > caller
> > > + * must start over anyway, so consider *cur_bytes undefined.
> > > */
> > > static int handle_dependencies(BlockDriverState *bs, uint64_t
> > > guest_offset,
> > > - unsigned int *nb_clusters)
> > > + uint64_t *cur_bytes)
> > > {
> > > BDRVQcowState *s = bs->opaque;
> > > QCowL2Meta *old_alloc;
> > > + uint64_t bytes = *cur_bytes;
> > >
> > > QLIST_FOREACH(old_alloc, &s->cluster_allocs, next_in_flight) {
> > >
> > > - uint64_t start = guest_offset >> s->cluster_bits;
> > > - uint64_t end = start + *nb_clusters;
> > > - uint64_t old_start = old_alloc->offset >> s->cluster_bits;
> > > - uint64_t old_end = old_start + old_alloc->nb_clusters;
> > > + uint64_t start = guest_offset;
> >
> > I'm not sure this is safe. Previously the function caught write
> > requests which overlap at cluster granularity, now it will allow them?
>
> At this point in the series, old_start and old_end are still aligned to
> cluster boundaries. So the cases in which an overlap is detected stay exactly
> the same with this patch. This is just a more precise description of what we
> really wanted to compare.
Good point. In an overlap comparison between A and B only one of them
needs to be cluster-aligned. I've used this trick myself in the past
but missed it in this code review.
Stefan
- [Qemu-devel] [RFC PATCH v2 00/23] qcow2: Delayed COW, Kevin Wolf, 2013/02/13
- [Qemu-devel] [RFC PATCH v2 05/23] qcow2: Factor out handle_alloc(), Kevin Wolf, 2013/02/13
- [Qemu-devel] [RFC PATCH v2 04/23] qcow2: Decouple cluster allocation from cluster reuse code, Kevin Wolf, 2013/02/13
- [Qemu-devel] [RFC PATCH v2 09/23] qcow2: Clean up handle_alloc(), Kevin Wolf, 2013/02/13
- [Qemu-devel] [RFC PATCH v2 08/23] qcow2: Finalise interface of handle_alloc(), Kevin Wolf, 2013/02/13
- [Qemu-devel] [RFC PATCH v2 07/23] qcow2: handle_alloc(): Get rid of keep_clusters parameter, Kevin Wolf, 2013/02/13
- [Qemu-devel] [RFC PATCH v2 12/23] qcow2: handle_copied(): Get rid of keep_clusters parameter, Kevin Wolf, 2013/02/13
- [Qemu-devel] [RFC PATCH v2 11/23] qcow2: handle_copied(): Get rid of nb_clusters parameter, Kevin Wolf, 2013/02/13
- [Qemu-devel] [RFC PATCH v2 06/23] qcow2: handle_alloc(): Get rid of nb_clusters parameter, Kevin Wolf, 2013/02/13
- [Qemu-devel] [RFC PATCH v2 15/23] qcow2: Allow requests with multiple l2metas, Kevin Wolf, 2013/02/13